predation by gray catbird on brown … by gray catbird on brown thrasher eggs james w. rivers* and...

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PREDATION BY GRAY CATBIRD ON BROWN THRASHER EGGS

JAMES W. RIVERS* AND BRETT K. SANDERCOCK

Kansas Cooperative Fish and Wildlife Research Unit, Division of Biology, Kansas State University,Manhattan, KS 66506 (JWR)

Division of Biology, Kansas State University, Manhattan, KS 66506 (BKS)Present address of JWR: Department of Ecology, Evolution, and Marine Biology, University of California,

Santa Barbara, CA 93106*Correspondent: [email protected]

ABSTRACT The gray catbird (Dumetella carolinensis) has been documented visiting and breakingthe eggs of artificial nests, but the implications of such observations are unclear because there islittle cost in depredating an undefended nest. During the summer of 2001 at Konza Prairie Bio-logical Station, Kansas, we videotaped a gray catbird that broke and consumed at least 1 egg in abrown thrasher (Toxostoma rufum) nest. Our observation was consistent with egg predation becausethe catbird consumed the contents of the damaged egg after breaking it. The large difference inbody mass suggests that a catbird (37 g) destroying eggs in a thrasher (69 g) nest might risk injuryif caught in the act of predation and might explain why egg predation by catbirds has been poorlydocumented. Our observation indicated that the catbird should be considered as an egg predatorof natural nests and that single-egg predation of songbird nests should not be attributed to eggremoval by female brown-headed cowbirds (Molothrus ater) without additional evidence.

RESUMEN El pajaro gato gris (Dumetella carolinensis) ha sido documentado visitando y rompien-do los huevos de nidos artificiales, pero las implicaciones de dichas observaciones no son clarasporque hay poco costo por depredar un nido sin defensa. Durante el verano de 2001 en KonzaPrairie Biological Station en Kansas, filmamos un pajaro gato gris que rompio y consumio por lomenos un huevo en un nido de un cuitlacoche cafe (Toxostoma rufum). Nuestra observacion esconsistente con la depredacion de huevos porque el pajaro gato consumio el contenido del huevodanado despues de romperlo. La gran diferencia en la masa corporal sugiere que un pajaro gato(37 g) destruyendo los huevos de un nido de cuitlacoche cafe (69 g) puede correr el riesgo deser lastimado si es descubierto en el acto de depredacion y puede explicar porque la depredacionde huevos por pajaros gato ha sido poco documentada. Nuestra observacion indica que el pajarogato debe ser considerado como depredador de huevos de nidos naturales y que la depredacionde un solo huevo de pajaros cantores no se debe atribuir a la extraccion hecha por una hembratordo copete cafe (Molothrus ater) sin evidencia adicional.

Egg pecking has been documented in sev-eral avian families, yet seems to be most wide-spread among wrens (Troglodytidae; Picmanand Picman, 1980; Quinn and Holroyd, 1989;Pribil and Picman, 1991) and mimic thrushes(Mimidae; Bowman and Carter, 1971; Wileyand Wiley, 1979; Sealy, 1994; Spooner et al.,1996). Within Mimidae, the gray catbird (Du-metella carolinensis) has been recorded visitingand pecking eggs in artificial nests (Belles-Islesand Picman, 1986; Spooner et al., 1996; Hau-ber, 1998; Zegers et al., 2000). The implica-tions of these observations for natural nests areunknown, however, because artificial nests areundefended and there is little cost in depre-dating an unguarded nest.

Documentation of egg predation by catbirdsat natural nests is limited, and it is unclear ifthe catbird should be considered an egg pred-ator. Sealy (1994) reported 2 separate obser-vations of egg predation by catbirds on easternkingbird (Tyrannus tyrannus) eggs in Manitoba.Here, we describe egg predation by a catbirdof a natural nest of a substantially larger bird,the brown thrasher (Toxostoma rufum).

During summer 2001, we studied nestingecology of brown thrashers on Konza PrairieBiological Station in northeastern Kansas(398059N, 978359W). Brown thrashers are abun-dant at Konza Prairie and nest at high densitiesin shrub patches of rough-leaved dogwood(Cornus drummondii) and American plum (Pru-

102 vol. 49, no. 1The Southwestern Naturalist

nus americana) on sites that are burned every3 to 5 years (Zimmerman, 1993; Cavitt andHaas, 2000). On 9 May 2001, we found a brownthrasher nest containing 5 eggs approximately45 cm off the ground in a dense stand ofAmerican plum. At the time of discovery, anadult was close to the nest giving the distinctive‘tchuck’ call that is commonly given around ac-tive nests (Cavitt and Haas, 2000). Within 20min of discovery, a blind used to house video-taping equipment was erected approximately1.5 m from the nest within the shrub patch.

On 10 May 2001, the nest was videotaped for2 h starting at 0806 CDT. At 1006 CDT, theblind, tripod, and video camera were removedwithout direct examination of the nest or itscontents. While reviewing the videotape of thebrown thrasher nest, we found that at 0940CDT an adult catbird (sex unknown) directlyapproached the nest in a furtive manner whileflicking and spreading its tail in an exaggerat-ed manner as it moved among shrubs near thenest. Once at the nest, the catbird peered intothe nest and struck 1 or more eggs with 4 hard,directed blows. It then consumed the yolk of 1damaged egg by sipping from the egg, raisingits bill to a 458 angle, and swallowing, repeatingthis series 4 times in quick succession. The birdpecked at the egg again briefly before it leftthe nest. The catbird spent 50 s at the nest andleft without removing eggs or eggshells. Twominutes later, the catbird returned to the nest,sat on the cup of the nest, probed the nest withits bill, and then made 2 hard, striking blowsinto the nest with its bill. It remained at thenest for 10 s, during which it did not sip yolkfrom the nest nor did it remove eggs or egg-shells. Within 5 s of delivering blows to theegg(s), the catbird was chased off camera by abrown thrasher. The catbird escaped from thevicinity before the thrasher could contact itphysically, and no thrasher approached thenest during the 27 min remaining in the vid-eotaping session. (A video clip of the interac-tion can be viewed at http://www.ksu.edu/bsanderc/movies/catbird.mpg.)

On 11 May 2001 at 1237 CDT, 1 egg wasmissing and the adult brown thrasher wasfound incubating 4 eggs in the nest. The bro-ken egg might have been removed by the cat-bird or by a thrasher as part of nest cleaning.On 18 May 2001 at 1050 CDT, the nest was

depredated; all eggs were missing and therewas no sign of adults or young in area.

Our observation augments previous reportsthat catbirds will destroy eggs in artificial nests(Hauber, 1998; Zegers et al., 2000) and in nat-ural nests of eastern kingbirds (Sealy, 1994).Two hypotheses proposed to explain heteros-pecific egg destruction behavior are resourcecompetition and egg predation (Pribil and Pic-man, 1991; Spooner et al., 1996). Gray catbirdsand brown thrashers use shrub patches forbreeding and foraging on Konza Prairie andhave similar timing of breeding ( J. W. Rivers,pers. obser.; Zimmerman, 1993). However, welack data on resource competition betweengray catbirds and brown thrashers on KonzaPrairie, and it is unknown if resource compe-tition influenced the egg predation event weobserved.

Our observation is consistent with egg pre-dation and corroborates the conclusion ofSpooner et al. (1994) that destruction of eggsby catbirds is for egg consumption. Sealy(1994) suggested that if egg destruction behav-ior had little cost, then predation might onlybe opportunistic. The large difference in bodymass (Cimprich and Moore, 1995; Cavitt andHaas, 2000) suggests that a catbird (37 g) de-stroying eggs in a thrasher (69 g) nest mightrisk injury if caught in the act of predation. Ifdepredation of heterospecific nests is a riskybehavior, it might explain why the catbird act-ed furtively near the thrasher nest, and whyegg predation by catbirds has been poorly doc-umented.

Our observation indicated that the catbirdshould be considered an egg predator of nat-ural nests. Moreover, single egg predation inshrub-nesting birds should not be attributedsolely to egg removal by female brown-headedcowbirds (Molothrus ater). Future studies thatvideotape nests could provide better documen-tation of egg predation by catbirds and allowfor determination of the costs and benefits ofthis behavior.

We thank J. Briskie, T. Brush, J. Cavitt, and 2 anon-ymous reviewers for helpful comments on the man-uscript and the Division of Biology at Kansas StateUniversity for support.

LITERATURE CITED

BELLES-ISLES, J. C., AND J. PICMAN. 1986. Destructionof heterospecific eggs by the gray catbird. WilsonBulletin 98:603–605.

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BOWMAN, R. I., AND A. CARTER. 1971. Egg-pecking be-haviour in Galapagos mockingbirds. Living Bird10:243–270.

CAVITT, J. F., AND C. A. HAAS. 2000. Brown thrasher(Toxostoma rufum). In: Poole, A., and F. Gill, edi-tors. The Birds of North America, number 557.The Birds of North America, Inc., Philadelphia,Pennsylvania.

CIMPRICH, D. A., AND F. R. MOORE. 1995. Gray catbird(Dumetella carolinensis). In: Poole, A., and F. Gill,editors. The Birds of North America, number167. The Birds of North America, Inc., Philadel-phia, Pennsylvania.

HAUBER, M. E. 1998. Single-egg removal from an ar-tificial nest by the gray catbird. Wilson Bulletin110:426–429.

MURPHY, M. T. 1996. Eastern kingbird (Tyrannus tyran-nus). In: Poole, A., and F. Gill, editors. The Birdsof North America, number 1253. The Birds ofNorth America, Inc., Philadelphia, Pennsylvania.

PICMAN, J., AND A. K. PICMAN. 1980. Destruction ofnests by the short-billed marsh wren. Condor 82:176–179.

PRIBIL, S., AND J. PICMAN. 1991. Why house wrens de-stroy clutches of other birds: a support for the

nest site competition hypothesis. Condor 93:184–185.

QUINN, M. S., AND G. L. HOLROYD. 1989. Nestling andegg destruction by house wrens. Condor 91:206–207.

SEALY, S. G. 1994. Observed acts of egg destruction,egg removal, and predation on nests of passerinebirds at Delta Marsh, Manitoba. Canadian Field-Naturalist 108:41–51.

SPOONER, A., S. PRIBIL, AND J. PICMAN. 1996. Why dogray catbirds destroy eggs in nests of other birds?Experimental tests of alternative hypotheses. Ca-nadian Journal of Zoology 74:1688–1695.

WILEY, J. W., AND B. N. WILEY. 1979. The biology ofthe white-crowned pigeon. Wildlife Monographs43:1–54.

ZEGERS, D. A., S. MAY, AND L. J. GOODRICH. 2000.Identification of nest predators at farm/forestedge and forest interior sites. Journal of Field Or-nithology 71:207–216.

ZIMMERMAN, J. L. 1993. The birds of Konza. Univer-sity Press of Kansas, Lawrence.

Submitted 15 March 2002. Accepted 7 May 2003.Associate Editor was Karen McBee.

ADDITIONAL RECORDS OF BIRDS FROM CUATRO CIENEGAS BASIN,NATURAL PROTECTED AREA, COAHUILA, MEXICO

ARMANDO J. CONTRERAS-BALDERAS,* JUAN H. LOPEZ-SOTO, JOSE MA. TORRES-AYALA, AND

SALVADOR CONTRERAS-ARQUIETA

Laboratorio de Ornitologıa, F.C.B., U.A.N.L., A.P. 425, San Nicolas de los Garza, Neuvo Leon, Mexico, 66450*Correspondent: [email protected]

ABSTRACT We recorded for the first time in Cuatro Cienegas Basin, Coahuila, Mexico, 43 spe-cies, 33 of them represented by specimens and 10 only by visual observations. These recordsincrease the species known for the basin by 38.4%. The fieldwork was conducted during 1996 and1997. Two species are new records for the state of Coahuila: Larus atricilla and Camptostoma imberbe.

RESUMEN Se registran por primera vez para el Valle de Cuatro Cienegas, Coahuila, Mexico, 43especies, 33 de ellas representadas por ejemplares y 10 solo son observaciones visuales. Con estosregistros se eleva en un 38.4% las especies conocidas para el citado valle. El trabajo se efectuoentre 1996–1997. Dos especies son nuevos registros para el estado de Coahuila: Larus atricilla yCamptostoma imberbe.

Recently, Contreras-Balderas et al. (1997)described seasonal and ecological distributionsof birds in Cuatro Cienegas Basin, Coahuila,Mexico, in a paper that included a review ofthe ornithological literature and a report of

108 species that they collected or observed inthe basin from April 1990 through March1991. Gonzalez-Rojas et al. (1999) reported 4new visual records of birds from this basin:Tachybaptus dominicus, Casmerodius albus, Co-


FIG. 1 Cuatro Cienegas Basin, Mexico. Areas shadowed correspond to mountains; white area color isCuatro Cienegas Basin.

ragyps atratus, and Thryothorus ludovicianus.Herein, we present new avian distribution re-cords supported by specimens from CuatroCienegas Basin (Fig. 1). These data were col-lected from November 1996 through Novem-ber 1997, and all are new records for the basin.All specimens were deposited in the Bird Col-lection, Laboratorio de Ornitologıa, Facultadde Ciencias Biologicas, Universidad Autonomade Nuevo Leon (UANL). Nomenclature andsystematic order follow American Ornitholo-gists’ Union (1998), season permanence fol-lows Howell and Webb (1995), and habitats(vegetational types) follow Henrickson andJohnston (1983).

SPECIES ACCOUNTS

Black-bellied Whistling-duck, Dendrocygna au-tumnalis. Specimens: Laguna Puente Zumba-dora (Las Playitas), UANL 2180 (male, testes12 3 3 mm; 11 April 1997), UANL 2181 (male,15 3 4 mm; 11 April 1997). Visual record: La-

guna Puente Zumbadora (Las Playitas), 12 in-dividuals on 11 April 1997. Habitat: aquatic.Seasonal permanence: unknown. Howell andWebb (1995) did not include Coahuila in thedistribution of the black-bellied whistling-duck,but Urban (1959) cited Evenden (1952), whoreported the species in a reservoir in southernCoahuila, along a railroad between Saltillo,Coahuila, and Avalos, Zacatecas. The status ofthis species is not well know, however, our 2male specimens showed gonadal development.

Blue-winged Teal, Anas discors. Specimens:Laguna Puente Zumbadora (Las Playitas),UANL 2185 (male, testes 9 3 3 mm; 12 April1997), UANL 2317 (female; 27 September1997), UANL 2318 (male; 27 September1997), UANL 2312 (male; 27 September1997), UANL 2313 (female; 27 September1997). Visual records: Laguna Puente Zumba-dora (Las Playitas), 16 individuals on 27 Sep-tember 1997 and 9 individuals on 28 Septem-ber 1997. Habitat: aquatic. Seasonal perma-nence: winter visitor.

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Cinnamon Teal, Anas cyanoptera. Specimen:0.9 km N of Antiguos Mineros del Norte,UANL 2212 (male, testes 17 3 9 mm; 12 May1997). Habitat: aquatic. Seasonal permanence:winter visitor. Howell and Webb (1995) citedcinnamon teal as winter visitor, and Urban(1959) reported this species during May.

Ruddy Duck, Oxyura jamaiscensis. Specimen:Laguna Puente Zumbadora (Las Playitas),UANL 2379 (29 November 1997). Visual re-cords: Laguna Puente Zumbadora (Las Playi-tas), 1 individual on 1 April 1997, 1 individualon 27 September 1997, and 35 individuals on29 November 1997. Habitat: aquatic. Seasonalpermanence: unknown. Howell and Webb(1995) reported ruddy duck as a breeding res-ident, but we collected and observed themonly during the fall.

Sharp-shinned Hawk, Accipiter striatus. Spec-imen: Poza Grande at Antiguos Mineros delNorte, UANL 2104 (male; 7 December 1996).Habitat: riparian. Seasonal permanence: win-ter visitor.

Northern Bobwhite, Colinus virginianus.Specimens: Poza Tıa Tecla, UANL 2303 (male;27 September 1997), UANL 2304 (female; 27September 1997), UANL 2305 (male; 27 Sep-tember 1997), UANL 2306 (male; 27 Septem-ber 1997), UANL 2307 (female; 27 September1997), UANL 2308 (female; 27 September1997), UANL 2309 (male; 27 September1997), UANL 2310 (male; 27 September1997). Visual records: Poza Tıa Tecla, 1 indi-vidual on 12 May 1997 and 45 individuals on27 September 1997; 9 km NNE of Antiguos Mi-neros del Norte, 6 individuals on 27 November1997. Habitat: riparian, mezquital, and dis-turbed areas. Seasonal permanence: residentbreeder.

Sandhill Crane, Grus canadensis. Specimen: 9km NNE of Antiguos Mineros del Norte,UANL 2362 (sex not determined; 27 Novem-ber 1997). Visual records: 1 km N of AntiguosMineros del Norte, 100 individuals on 5 De-cember 1996, 47 individuals on 14 March 1997,and 85 individuals on 15 March 1997; 0.9 kmN of Antiguos Mineros del Norte, 150 individ-uals on 27 November 1997. Habitat: salt-toler-ant grasses and disturbed areas. Seasonal per-manence: winter visitor. Howell and Webb(1995) and Sibley (2000) did not include Coa-huila in the distribution of the sandhill crane,but Sutton and Burleigh (1939) remarked that

a flock of sandhill cranes was heard near May-ran during January. We found this species dur-ing the fall and winter seasons in Cuatro Cie-negas Basin.

Black-necked Stilt, Himantopus mexicanus.Specimens: 0.9 km N of Antiguos Mineros delNorte, UANL 2213 (male, testes 10 3 4 mm;12 May 1997), UANL 2214 (female, ovule indevelopment, 25 3 25 mm and 25 3 20 mm;12 May 1997). Visual records: 0.9 km N of Anti-guos Mineros del Norte, 5 individuals on 12May 1997. Habitat: aquatic. Seasonal perma-nence: nonbreeding visitor.

Long-billed Curlew, Numenius americanus.Specimen: 9 km NNE of Antiguos Mineros delNorte, UANL 2366 (female; 27 November1997). Visual records: 13 km NNE of AntiguosMineros del Norte, 40 individuals on 15 March1997; 9 km NNE of Antiguos Mineros del Nor-te, 1 individual on 27 November 1997). Habi-tat: disturbed areas. Seasonal permanence:winter visitor.

White-winged Dove, Zenaida asiatica. Speci-mens: Poza Grande at Antiguos Mineros delNorte, UANL 2103 (female; 7 December1996); Antiguos Mineros del Norte, UANL2298 (male; 26 September 1997), UANL 2299(male; 26 September 1997), UANL 2300 (fe-male; 26 September 1997). Visual records:Poza Grande at Antiguos Mineros del Norte, 1individual on 5 December 1996 and 1 individ-ual on 7 December 1996; Poza Grande at Anti-guos Mineros del Norte, 12 individuals on 12May 1997, 8 individuals on 13 May 1997, and30 individuals on 26 September 1997; Poza laTıa Tecla, 4 individuals on 12 May 1997; 17 kmNNE of Antiguos Mineros del Norte, 1 individ-ual on 12 May 1997. Habitat: riparian, mez-quital, and disturbed areas. Seasonal perma-nence: resident breeder.

Common Ground-dove, Columbina passerina.Specimen: 7 km WNW of Cuatro Cienegas,UANL 2275 (female; 25 September 1997). Vi-sual records: Poza Orozco, 2 individuals on 13May 1997, 2 individuals on 20 August 1997,and 4 individuals on 26 September 1997; PozaLa Becerra, 2 individuals on 19 June 1997.Habitat: alkali scrub, riparian, and mezquital.Seasonal permanence: resident breeder. Ur-ban (1959), Howell and Webb (1995), and Sib-ley (2000) included only northern Coahuila inthe distribution of the common ground-dove.Its presence in Cuatro Cienegas Basin extends


the breeding range of the common ground-dove to the south.

Yellow-billed Cuckoo, Coccyzus americanus.Specimen: 0.2 km WNW of Poza Orozco,UANL 2259 (female, gonadal development; 21June 1997). Habitat: alkali scrub. Seasonal per-manence: nonbreeding visitor. Howell andWebb (1995) listed the yellow-billed cuckoo asa nonbreeding visitor in Coahuila, but wefound a female exhibiting gonadal develop-ment.

Eastern Screech-owl, Otus asio. Specimens:Poza Orozco, UANL 2236 (male, testes 6 3 4mm; 13 May 1997), UANL 2237 (female, go-nadal development; 14 May 1997). Habitat: ri-parian. Seasonal permanence: resident breed-er.

Common Poorwill, Phalaenoptilus nuttallii.Specimens: 6 km NW of Antiguos Mineros delNorte, UANL 2085 (male; 6 December 1996);Poza La Becerra, UANL 2161 (female; 13March 1997). Habitat: alkali scrub and salt-tol-erant grasses. Seasonal permanence: residentbreeder.

Yellow-bellied Sapsucker, Sphyrapicus varius.Specimen: Poza Grande at Antiguos Minerosdel Norte, UANL 2081 (male; 6 December1996). Habitat: riparian. Seasonal perma-nence: winter visitor.

Eastern Wood-pewee, Contopus virens. Speci-mens: 0.2 km WNW of Poza Orozco, UANL2268 (male; 20 August 1997), UANL 2271(male; 21 August 1997), and UANL 2272 (fe-male; 21 August 1997). Visual records: 0.2 kmWNW of Poza Orozco, 3 individuals on 21 Au-gust 1997. Habitat: alkali scrub. Seasonal per-manence: nonbreeding visitor. Howell andWebb (1995) and Sibley (2000) did not in-clude Coahuila in the distribution of the east-ern wood-pewee from, but Urban (1959) men-tioned it as an uncommon transient in Coa-huila.

Least Flycatcher, Empidonax minimus. Speci-men: 0.5 km N of Poza El Anteojo, UANL 2177(female; 11 April 1997). Habitat: alkali scrub.Seasonal permanence: nonbreeding visitor.

Gray Flycatcher, Empidonax wrightii. Speci-men: Poza Grande at Antiguos Mineros delNorte, UANL 2097 (male; 7 December 1996).Habitat: riparian. Seasonal permanence: win-ter visitor.

Western Kingbird, Tyrannus verticalis. Speci-men: Poza Orozco, UANL 2240 (female; 14

May 1997). Visual records: Antiguos Minerosdel Norte, 4 individuals on 12 May 1997; PozaOrozco, 6 individuals on 14 May 1997 and 2individuals on 19–21 June 1997. Habitat: ripar-ian, alkali scrub, and disturbed areas. Seasonalpermanence: nonbreeding visitor.

Chihuahuan Raven, Corvus cryptoleucus.Specimen: Laguna Puente Zumbadora (LasPlayitas), UANL 2184 (male; 12 April 1997).Visual record: Laguna Puente Zumbadora (LasPlayitas), 1 individual on 12 April 1997. Habi-tat: salt-tolerant grasses. Seasonal permanence:resident breeder?

Cave Swallow, Petrochelidon fulva. Specimens:Poza Orozco, UANL 2238 (male; 14 May1997), UANL 2239 (female; 14 May 1997); 4.5km NW of Poza Orozco, UANL 2253 (male; 21June 1997), UANL 2254 (male; 21 June 1997),and UANL 2255 (male; 21 June 1997). Visualrecords: Poza Orozco, 1 individual on 17 Jan-uary 1997 and 18 individuals 14 May 1997;Antiguos Mineros del Norte, 6 individuals on12 May 1997 and 4 individuals on 13 May 1997;4.5 km NW of Poza Orozco, 75 individuals on21 June 1997; 4.5 km SSE of Antiguos Minerosdel Norte, 25 individuals on 21 June 1997; 0.2km WNW of Poza Orozco, 6 individuals on 21June 1997. Habitat: alkali scrub and disturbedareas. Seasonal permanence: resident breeder.

Mountain Bluebird, Sialia currucoides. Speci-mens: extreme S of Dunas Blancas, UANL2146 (male; 2 February 1997), UANL 2152 (fe-male; 3 February 1997), UANL 2153 (male, 3February 1997); extreme E of Dunas Blancas,UANL 2144 (female; 2 February 1997), UANL2145 (male; 2 February 1997), UANL 2148 (fe-male; 2 February 1997), UANL 2149 (male; 2February 1997). Visual records: extreme S ofDunas Blancas, 29 individuals on 2 February1997 and 12 individuals on 3 February 1997;Ejido 6 de Enero, 2 individuals on 14 March1997. Habitat: gypsophilous scrub and dis-turbed areas. Seasonal permanence: winter vis-itor.

American Robin, Turdus migratorius. Speci-mens: Poza Grande at Antiguos Mineros delNorte, UANL 2101 (male; 7 December 1996),UANL 2175 (male; 15 March 1997). Visual re-cords: Poza Grande at Antiguos Mineros delNorte, 7 individuals on 7 December 1996; PozaGrande at Antiguos Mineros del Norte, 4 in-dividuals on 15 March 1997; Poza Orozco, 1

March 2004 107Notes

individual on 18 January 1997. Habitat: ripari-an. Seasonal permanence: winter visitor.

Crissal Thrasher, Toxostoma crissale. Speci-mens: 3.2 km NW of San Marcos, UANL 2341(male; 19 October 1997); 7 km WNW of Cua-tro Cienegas, UANL 2279 (female; 25 Septem-ber 1997). Habitat: mezquital and alkali scrub.Seasonal permanence: resident breeder.

Cedar Waxwing, Bombycilla cedrorum. Speci-mens: Poza Orozco, UANL 2117 (male; 17 Jan-uary 1997), UANL 2118 (female; 17 January1997), UANL 2234 (female; 13 May 1997). Vi-sual records: Poza Orozco, 85 individuals on 17January 1997 and 30 individuals on 13 May1997; 8 km SE of Ejido 6 de Enero, 4 individ-uals on 4 February 1997. Habitat: riparian, salt-tolerant grasses, and disturbed areas. Seasonalpermanence: winter visitor.

Nashville Warbler, Vermivora ruficapilla. Spec-imen: Laguna Puente Zumbadora (Las Playi-tas), UANL 2315 (male; 27 September 1997).Habitat: alkali scrub. Seasonal permanence:nonbreeding visitor.

Louisiana Waterthrush, Seiurus motacilla.Specimen: Poza Orozco, UANL 2169 (female;14 March 1997). Habitat: riparian. Seasonalpermanence: winter visitor. Sibley (2000) didnot include Coahuila in the distribution of theLouisiana waterthrush, but Howell and Webb(1995) included them in the extreme north-eastern portion of the state, and, combinedwith our record, this is a notable increase inthe winter distribution.

Rufous-crowned Sparrow, Aimophila ruficeps.Specimen: Poza Azul, UANL 2354 (sex un-known; 20 October 1997). Habitat: salt-toler-ant grasses. Seasonal permanence: residentbreeder.

Grasshopper Sparrow, Ammodramus savan-narum. Specimens: 7 km WNW of Cuatro Cie-negas, UANL 2277 (male; 25 September 1997),UANL 2278 (male; 25 September 1997); RioMezquites, UANL 2325 (male; 17 October1997), UANL 2332 (male; 18 October 1997);Poza Azul, UANL 2352 (male; 20 October1997). Habitat: salt-tolerant grasses and alkaliscrub. Seasonal permanence: winter visitor.

Varied Bunting, Passerina versiolor. Specimen:Poza Tıa Tecla, UANL 2221 (female, gonadaldevelopment; 12 May 1997). Habitat: riparian.Seasonal permanence: summer resident.

Brewer’s Blackbird, Euphagus cyanocephalus.Specimens: Antiguos Mineros del Norte,

UANL 2171 (male; 15 March 1997); 0.9 km Nof Antiguos Mineros del Norte, UANL 2301(male; 27 September 1997), UANL 2302 (fe-male; 27 September 1997); Poza Azul, UANL2342 (female; 19 October 1997), UANL 2343(male; 19 October 1997), UANL 2345 (male;19 October 1997), UANL 2346 (male; 19 Oc-tober 1997), UANL 2355 (female; 20 October1997), UANL 2361 (female; 20 October 1997).Visual records: Antiguos Mineros del Norte, 18individuals on 15 March 1997 and 75 individ-uals on 26 September 1997; Poza Azul, 120 in-dividuals on 19 October 1997 and 70 individ-uals on 20 October 1997. Habitat: salt-tolerantgrasses and disturbed areas. Seasonal perma-nence: winter visitor.

Pine Siskin, Carduelis pinus. Specimen: PozaGrande at Antiguos Mineros del Norte, UANL2098 (male; 7 December 1996). Visual records:Cuatro Cienegas, 25 individuals on 10 April1997. Habitat: riparian and disturbed areas.Seasonal permanence: winter visitor.

American Goldfinch, Carduelis tristis. Speci-men: Poza Grande at Antiguos Mineros delNorte, UANL 2172 (female; 15 March 1997).Habitat: riparian. Seasonal permanence: win-ter visitor.

Other species that were visually registered inthe basin as new records but lack voucher spec-imens were:

Neotropic Cormorant, Phalacrocorax brasilia-nus. Laguna Puente Zumbadora (Las Playitas),1 individual on 11 April 1997, 1 individual on27 September 1997, and 1 individual on 28 No-vember 1997. Habitat: aquatic. Seasonal per-manence: unknown. Howell and Webb (1995)reported the Neotropic cormorant as residentbreeder, but we do not have evidence of breed-ing, and we consider its breeding status as un-known. This species is expanding its distribu-tion.

American Bittern, Botaurus lentiginosus. RioMezquites, 1 individual on 18 October 1997and 1 individual on 26 June 2002. Habitat: ri-parian. Seasonal permanence: unknown. Ho-well and Webb (1995) included the Americanbittern as a winter visitor, but on 26 June 2002,D. Hendrickson and M. Crisp (University ofTexas-Austin, pers. comm.) reported a speci-men on Rio Mezquites at 268559240N,1028049270W. It displayed distraction behavior,which suggested that it likely had a nest nearby.


Although confirmation is lacking, this speciesis probably a breeding resident.

White-faced Ibis, Plegadis chihi. Laguna Pu-ente Zumbadora (Las Playitas), 5 individualson 28 September 1997. Habitat: aquatic. Sea-sonal permanence: winter visitor.

Osprey, Pandion haliaethus. Laguna PuenteZumbadora (Las Playitas), 2 individuals on 27September 1997. Habitat: aquatic. Seasonalpermanence: nonbreeding visitor.

Peregrine Falcon, Falco peregrinus. LagunaPuente Zumbadora (Las Playitas), 1 individu-al on 28 September 1997 and 1 individual on29 November 1997. Habitat: alkali scrub. Sea-sonal permanence: unknown. Howell andWebb (1995) listed the peregrine falcon as aresident breeder, but we observed this speciesonly in September and November. We consid-er its status to be unknown, although theyprobably nest in the mountains around thebasin.

Laughing Gull, Larus atricilla. Laguna Pu-ente Zumbadora (Las Playitas), 1 individual on12 April 1997. Habitat: aquatic. Seasonal per-manence: probably nonbreeding visitor.

Herring Gull, Larus argentatus. Laguna Pu-ente Zumbadora (Las Playitas), 15 individualson 28 November 1997 and 5 individuals on 29November 1997. Habitat: aquatic. Seasonalpermanence: winter visitor.

White-throated Swift, Aeronautes saxatilis.Poza Grande at Antiguos Mineros del Norte, 1individual on 6 December 1996. Habitat: ripar-ian. Seasonal permanence: unknown. Howelland Webb (1995) cited the white-throated swiftas a resident breeder, but we observed themonly one time, during December. We considerit to be a winter visitor or unknown.

Northern Beardless-tyrannulet, Camptostomaimberbe. Poza Orozco. 1 individual on 19 June1997. Habitat: riparian. Seasonal permanence:unknown. The northern beardless-tyrannuletprobably nests in the basin, but we have only1 observation for June; no more informationis available to support this position. Howell andWebb (1995) did not report this species forCoahuila.

Canyon Towhee, Pipilo fuscus. 6 km NW ofAntiguos Mineros del Norte, 1 individual on 7December 1996. Habitat: alkali scrub. Seasonalpermanence: unknown. Howell and Webb(1995) listed the canyon towhee as a residentbreeder, but we have only 1 observation in a

canyon, even though we visited this area sev-eral times during 1 year. We have not observedthem during other seasons, so we consider thebreeding status to be unknown.

Of the 43 species recorded in this paper, 38were expected and 5 were unexpected. Theseasonalities of the reported species were 17winter visitors, 9 resident breeders, 8 non-breeding visitors, 1 summer resident, and 8 ofunknown status. Additionally, 2 species werenew records from Coahuila: laughing gull (L.atricilla) and northern beardless-tyrannulet (C.imberbe). Supplementing reports by Contreras-Balderas et al. (1997) and Gonzalez-Rojas(1999), the avifauna from Cuatro Cienegas Ba-sin in Coahuila includes 155 species. The 43new species we have added represent a 38.4%increase; 10 of these are visual records, and 33are represented by specimens. The avifaunafrom this basin is dynamic and will require ad-ditional field study to be fully documented.

We thank Comision Nacional para el Conocimien-to y Uso de la Biodiversidad (CONABIO) for sup-porting this project, Instituto Nacional de Ecologıa(formerly Secretarıa del Medio Ambiente, RecursosNaturales y Pesca [SEMARNAP], now Secretarıa delMedio Ambiente y Recursos Naturales [SEMAR-NAT]) for the collection permit, and Direccion delArea Protegida del Valle de Cuatro Cienegas for fa-cilities for the fieldwork.

LITERATURE CITED

AMERICAN ORNITHOLOGISTS’ UNION. 1998. Check-listof North American birds, sixth edition. AmericanOrnithologists’ Union, New York.

CONTRERAS-BALDERAS, A. J., J. A. GARCIA-SALAS, AND J.I. GONZALEZ-ROJAS. 1997. Seasonal and ecologicaldistribution of birds from Cuatro Cienegas, Coa-huila, Mexico. Southwestern Naturalist 42:224–228.

EVENDEN, F. G., JR. 1952. Notes on Mexican birdsdistribution. Wilson Bulletin 64:112–113.

GONZALEZ-ROJAS, J. I., A. J. CONTRERAS-BALDERAS, A.GUZMAN-VELASCO, AND J. A. GARCıA-SALAS. 1999.Nuevos registros de aves para el Valle de Cuatro-cienegas, Coahuila, Mexico. Vertebrata Mexicana6:1–3.

HENRICKSON, J., AND M. C. JOHNSTON. 1986. Vegeta-tion and community types of the ChihuahuanDesert. In: Barlow, J. C., A. M. Powell, and B. N.Timmerman, editors. Transactions of the secondsymposium on resources of the Chihuahuan De-sert region, United States and Mexico. Chihua-

March 2004 109Notes

huan Desert Research Institute, Alpine, Texas.Pp. 20–39.

HOWELL, S. N. G., AND S. WEBB. 1995. A guide to thebirds of Mexico and Central America. OxfordUniversity Press, New York.

SIBLEY, D. A. 2000. The Sibley guide to birds. AlfredA Knopf, New York.

SUTTON, G. M., AND T. D. BURLEIGH. 1939. A list ofbirds observed on the 1938 Semple Expedition

to northeastern Mexico. Occasional Papers of theMuseum of Zoology, Louisiana State University 3:15–46.

URBAN, E. K. 1959. Birds from Coahuila, Mexico.University of Kansas Publications, Museum ofNatural History 11(8):445–516.

Submitted 8 March 2001. Accepted 27 March 2003.Associate Editor was Geoffrey C. Carpenter.

INTERSPECIFIC INTERACTIONS BETWEEN BADGERS AND RED-TAILEDHAWKS IN THE SONORAN DESERT, SOUTHWESTERN ARIZONA

PATRICK K. DEVERS,* KIANA KOENEN, AND PAUL R. KRAUSMAN

Wildlife and Fisheries Program, School of Renewable Natural Resources, The University of Arizona,Tucson, AZ 85721

Present address of PKD: Department of Fisheries and Wildlife, Virginia Polytechnic and State University,Blacksburg, VA 24061-0321

*Correspondent: [email protected]

ABSTRACT Interspecific and intraspecific relationships have received much attention from ecol-ogists and play an important role in the structure of wildlife communities, but researchers haverarely attempted to study interactions between phylogenetically unrelated organisms. We observed6 interactions between badgers (Taxidea taxus) and red-tailed hawks (Buteo jamaicensis) betweenFebruary and June 1999 on the Barry M. Goldwater Tactical Range (328539060N, 1128439240W)near Ajo, Arizona. Each interaction lasted 5 to 20 minutes. Interactions were characterized by ared-tailed hawk following a badger as it searched for prey. On 2 occasions, red-tailed hawks ap-parently attempted to take prey items escaping from a badger. Badgers and red-tailed hawks feedprimarily on small mammals, suggesting possible competition between the 2 species. Further re-search is needed to determine if badgers and red-tailed hawks in the Sonoran Desert are com-peting for a limiting resource or if one species (presumably the red-tailed hawk) is benefitingfrom the interaction without affecting the other species (badger).

RESUMEN Las relaciones inter e intraespecıficas han recibido mucha atencion por parte deecologos y juegan un papel importante en la estructura de las comunidades de fauna silvestre,pero los investigadores raramente intentan estudiar interacciones entre organismos filogenetica-mente no relacionados. Observamos 6 interacciones entre tejones (Taxidea taxus) y aguilillas co-liroja (Buteo jamaicensis) entre febrero y junio de 1999 en la zona de Barry M. Goldwater TacticalRange (328539060N, 1128439240O) cerca de Ajo, Arizona. Cada interaccion duro de 5 a 20 minutos.Las interacciones consistieron en el seguimiento de una aguililla coliroja a un tejon mientrasbuscaba presas. En 2 ocasiones, una aguililla coliroja aparentemente intento tomar una presa quese escapaba del tejon. Los tejones y las aguilillas coliroja se alimentan principalmente de mamı-feros pequenos, lo que sugiere una posible competencia entre las 2 especies. Se necesita masinvestigacion para determinar si los tejones y las aguilillas coliroja en el desierto Sonorense estancompitiendo por un recurso limitado o si una de las especies (presumiblemente la aguililla coli-roja) se beneficia de la interaccion sin afectar a la otra especie (el tejon).

Intraspecific and interspecific relationshipshave received much attention from ecologistsand play an important role in the structure ofwildlife communities (Smith, 1980). Tradition-

ally, ecologists have concentrated research ef-forts on interactions between closely relatedorganisms but have rarely attempted to studyphylogenetically unrelated organisms (Capizzi


and Luiselli, 1996). Despite the lack of re-search, interspecific relationships between un-related organisms are common and deservegreater attention (Polis and McCormick,1987). We report on several observations of in-terspecific interactions between badgers (Taxi-dea taxus) and red-tailed hawks (Buteo jamaicen-sis) in the Sonoran Desert of southwestern Ar-izona.

We observed 6 separate interactions betweenbadgers and red-tailed hawks from Februarythrough June 1999 on the Barry M. GoldwaterTactical Range (328539060N, 1128439240E) nearAjo, Arizona. Field personnel made detailedobservations of 2 interactions from distances of1 to 3 km using 603 Swarovski spotting scopes(Swarovski, Inc., Austria). Each interaction last-ed 5 to 20 min. The first interaction occurredon 11 February 1999 at 1618 MST and involved2 red-tailed hawks and 1 badger. The badgerwas observed moving among creosote bushes(Larrea tridentata) and seemed to be searchingfor prey. The badger flushed a covey of quail(Callipepla) and 1 red-tailed hawk from behinda creosote bush. The red-tailed hawk circledlow over the badger and the badger scurriedaway. A second red-tailed hawk was then ob-served landing at the quail flush site. Visualcontact with the badger was lost, and the red-tailed hawks flew away. Neither of the red-tailed hawks was observed attacking the bad-ger; thus, we do not believe the red-tailedhawks were attempting to prey on the badger.Additionally, red-tailed hawks are known toprey on small mammals (i.e., mice) and bad-gers are presumably too large for red-tailedhawks to prey upon.

The second observation occurred on 11 May1999 at 0822 MST. One badger was observedapparently searching for food at the base ofcreosote bushes while a red-tailed hawkwatched from a perch site about 2 to 4 m away.After about 10 min, the red-tailed hawkswooped down on the badger as it was diggingat the base of a creosote bush. The badgerlunged at the red-tailed hawk and apparentlychased it away. We were unable to determineif the badger or red-tailed hawk captured aprey item. Visual contact with the badger waslost when it moved into a patch of mesquite(Prosopis). Approximately 5 min later, presum-ably the same badger was observed moving out

of the mesquite and was followed by a red-tailed hawk (possibly the same hawk) thatperched in a creosote bush and watched thebadger as it apparently searched for prey. Thered-tailed hawk was observed moving 3 timesfrom perch to perch to stay within a few metersof the badger as it searched for prey. Obser-vations were continued until visual contact waslost on both animals.

Similar interactions were observed on 4 oth-er occasions, although detailed notes were notrecorded. Each interaction was characterizedby a red-tailed hawk following a badger as itapparently searched for prey. Though badgersand red-tailed hawks feed primarily on smallmammals, particularly sciurids (Mader, 1978;Messick and Hornocker, 1981; Millsap, 1981;Cockrum, 1982; Marti et al., 1993), suggestingpossible competition between the 2 species, wecannot conclude what type of ecological inter-action (if any) was occurring between thesespecies. Similar interactions have been report-ed between the Aplomado falcon (Falco femo-ralis) and maned wolf (Chrysocon brachyurus) incentral Brazil (Silveria et al., 1997) and be-tween the martial eagle (Polemaetus bellicosus)and honey badger (Mellivora capensis) in Hwan-ge National Park, Zimbabwe (Erwee, 1988).Additionally, hunting interactions between coy-otes (Canis latrans) and badgers (Kiliaan et al.,1991; Minta et al., 1992) have been reported.Further research is needed to elucidate possi-ble ecological relationship between badgersand red-tailed hawks in the Sonoran Desert.

We thank K. Barnes and J. Weiss for making fieldobservations and S. Destafeno for suggestions andencouragement on writing this manuscript. Field ob-servations were made during a Sonoran pronghorn(Antilocapra americana sonoranensis) behavior studyfunded by the United States Air Force.

LITERATURE CITED

CAPIZZI, D., AND L. LUISELLI. 1996. Feeding relation-ships and competitive interactions between phy-logenetically unrelated predators (owls andsnakes). Ecologica 17:265–284.

COCKRUM, E. L. 1982. Mammals of the Southwest.University of Arizona Press, Tucson.

ERWEE, H. P. 1988. Martial eagle and honey badgerencounter. Honeyguide 34:27.

KILIAAN, H. P. L., C. MAMO, AND P. C. PAQUET. 1991.

March 2004 111Notes

A coyote (Canis latrans) and badger (Taxidea tax-us) interaction near Cypress Hills Provincial Park,Alberta. Canadian Field Naturalist 105:122–123.

MADER, W. J. 1978. A comparative nesting study ofred-tailed hawks and Harris’ hawks in southernArizona. Auk 95:327–337.

MARTI, C. D., K. STEENHOF, M. N. KOCKET, AND J. S.MARKS. 1993. Community trophic structure therole of diet, body size, and activity in vertebratepredators. Oikos 67:6–18.

MESSICK, J. P., AND M. G. HORNOCKER. 1981. Ecologyof the badger in southwestern Idaho. WildlifeMonographs Number 76.

MILLSAP, B. A. 1981. Distributional status of Falco-niformes in west-central Arizona: with notes onecology, reproductive success and management.United States Department of Interior, Bureau ofLand Management, Technical Note 355.

MINTA, S. C., K. A. MINTA, AND D. F. LOTT. 1992.Hunting associations between badgers (Taxideataxus) and coyotes (Canis latrans). Journal ofMammalogy 73:814–820.

POLIS, G. A., AND S. J. MCCORMICK. 1987. Intraguildpredation and competition among desert scor-pions. Ecology 68:332–343.

SILVERIA, L., A. T. H. JACOMO, F. H. G. RODRIGUES,AND P. G. CRAWSHAW, JR. 1997. Hunting associa-tions between the Aplomado falcon (Falco fermo-ralis) and the manded wolf (Chrysocyon brachyu-rus) in Emas National Park, central Brazil. Con-dor 99:201–202.

SMITH, R. L. 1980. Ecology and field biology, thirdedition. Harper and Row Publishers, New York.

Submitted 8 January 2002. Accepted 10 February 2003.Associate Editor was Loren K. Ammerman.

WESTWARD EXPANSION OF THE EASTERN FOX SQUIRREL(SCIURUS NIGER) IN NORTHEASTERN NEW MEXICO AND

SOUTHEASTERN COLORADO

KEITH GELUSO*

Department of Biology, University of New Mexico, Albuquerque, NM 87131*Correspondent: [email protected]

ABSTRACT The eastern fox squirrel (Sciurus niger) has continued to move westward along ri-parian corridors in the southwestern United States. This species is now established along theArkansas River and its major tributaries in southeastern Colorado. In addition, a population of S.niger exists in northern New Mexico, and this population might be the result of natural expansionfrom populations along the Purgatoire River in southeastern Colorado.

RESUMEN El area de distribucion de la ardilla zorra (Sciurus niger) se ha expandido continua-mente hacia el oeste en el suroeste de los Estados Unidos a lo largo de corredores riparios. Estaespecie ya esta establecida a lo largo del rıo Arkansas y en sus tributarios principales en el surestede Colorado. Ademas, una poblacion de S. niger existe en el norte de Nuevo Mexico, y puede serel resultado de una expansion natural de poblaciones a lo largo del rıo Purgatoire del sureste deColorado.

Changes in land use, such as suppression ofprairie fires, elimination of native grazers,planting of native and exotic trees, and alter-ation of flow regimes in rivers, have increasedforests and woodland corridors, especiallyalong waterways in the Great Plains (Tomelle-ri, 1984; Johnson, 1994). These new riparianwoodlands have been suggested as the causefor westward expansion of a number of wood-

land mammals into prairie regions of theGreat Plains (Choate and Krause, 1974; Choateand Reed, 1986; Sparks and Choate, 1995; Wil-son and Choate, 1996; Bogan, 1997; Benedictet al., 2000; Bogan and Cryan, 2000; Sparksand Choate, 2000). The eastern fox squirrel(Sciurus niger) is an example of a woodlandspecies that has spread westward along ripariancorridors in western portions of its range, in-


FIG. 1 Distribution of the eastern fox squirrel (Sciurus niger) in Colorado, New Mexico, and adjacentstates. Triangles represent introduced populations. Circles in Kansas, Oklahoma, and Texas represent nativepopulations. Circles in Colorado and New Mexico represent populations suspected of natural colonization,although some introductions are known (see text). Unshaded symbols in New Mexico and Colorado rep-resent new records (Appendix 1). Shaded symbols in all states represent previously published records(NM Frey and Campbell, 1997; TX Jones et al., 1988; Davis and Schmidly, 1994; Choate, 1997; KS Beeet al., 1981; OK Caire et al., 1989; and CO Armstrong, 1972; Fitzgerald et al., 1994). Shading and trianglesrepresent the present distribution of eastern fox squirrels in the study area.

cluding areas of Texas, northeastern Colorado,Nebraska, North Dakota, Montana, and Sas-katchewan (Hoover and Yeager, 1953; Hib-bard, 1956; Jones, 1964; Hoffman et al., 1969;Adam, 1984; Knapp and Swenson, 1986; Fitz-gerald et al., 1994; Choate, 1997). To date how-ever, no published locality record exists for S.niger in northeastern New Mexico and south-eastern Colorado.

Frey and Campbell (1997) recently reportedon the distribution of eastern fox squirrels inNew Mexico. They provided historical ac-

counts for populations in Chaves County (Ros-well and Bitter Lakes National Wildlife Ref-uge), Eddy County (Carlsbad and near BlackRiver Village), Lea County (Lovington andHobbs), and Lincoln County (Hondo; Fig. 1).Thus far, S. niger is known only from south-eastern New Mexico, and all of these popula-tions are the result of human introductions(Frey and Campbell, 1997).

In Colorado, Armstrong (1972), Hall(1981), and Koprowski (1994) reported theeastern fox squirrel mostly from northeastern

March 2004 113Notes

sections of the state. Although Fitzgerald et al.(1994) mapped the distribution of this squirrelto include most of eastern Colorado and Lech-leitner (1969) noted that S. niger was firmly es-tablished along the Arkansas River drainage, Iknow of no published locality record fromsoutheastern Colorado, except for the intro-duced population in Colorado Springs, El PasoCounty (Warren, 1942).

I report the continued westward movementof eastern fox squirrels in northeastern NewMexico and southeastern Colorado. This studywas initiated after I observed an eastern foxsquirrel in northeastern New Mexico and be-gan to investigate whether this population wasresult of human introduction or the first nat-ural population of S. niger in New Mexico.

In 2000 and 2001, I queried museums, in-vestigated leads from C. A. Meaney (DenverMuseum of Natural History, in litt.), contactedlocal residents, and searched for squirrels todetermine the present distribution of S. nigerin Colorado and New Mexico. In particular, Iexamined 2 river systems, the Canadian andthe Purgatoire, as possible corridors for dis-persal of S. niger into northeastern New Mexi-co.

On 5 September 1999, I observed an adultS. niger in Raton, Colfax County, New Mexico(Fig. 1), in an area containing small deciduoustrees. This location is bordered by Mount Cal-vary Cemetery and Raton High School; bothcontain large trees. On 16 December 2000, Ialso observed 2 adult S. niger near the ColfaxCounty Courthouse. Many additional sightingsof these squirrels have been made in a nearbyresidential area in Raton for at least 4 years (Z.Yaksich, pers. comm.).

I interviewed several long-time residents todetermine how long S. niger has been presentin Raton. One resident remembers seeingsquirrels as early as the late 1950s (A. Mangini,pers. comm.); however, he was not positive thatthey were S. niger. In the same neighborhood,another resident had bird feeders during the1970s and 1980s, and he never observed squir-rels in his yard or elsewhere in town (G. R.Yaksich, pers. comm.). In contrast, I spoke to2 residents in the same neighborhood withbird feeders today; both observe eastern foxsquirrels frequently (Z. Yaksich and B. K. Yak-sich, pers. comm.). Thus, S. niger is likely a re-cent arrival to Raton, because sightings of

squirrels were infrequent until recently and be-cause squirrels were absent around bird feed-ers in the 1970s and 1980s. The report of squir-rels from the 1950s might have been sightingsof other sciurids, including the rock squirrel(Spermophilus variegatus) or Abert’s squirrel(Sciurus aberti), both of which are known fromColfax County (Findley et al., 1975).

After discovering the population of S. nigerin Raton, I examined several areas along theCanadian River for a possible dispersal routefrom the nearest population of this squirrel inTexas. The Canadian River flows 5 km southof Raton, New Mexico and continues southand east for 325 km before reaching Texas(Fig. 1). In Texas, S. niger occurs 70 km east ofthe border along the Canadian River in Old-ham County ( Jones et al., 1988). Along the riv-er, I observed scattered cottonwoods (Populus)and fairly continuous stands of saltcedar (Ta-marix) from Raton to Maxwell and east ofSpringer (5 km S Raton to Maxwell along In-terstate Highway 25, Colfax County; 9 km ESpringer on US Highway 56, Colfax County).Farther south, I observed scattered patches ofsaltcedar but no large deciduous trees nearRoy and Sanchez (16 km W Roy on NM High-way 120, Harding and Mora counties; 6 km NESanchez on NM Highway 419, San MiguelCounty). Along the banks of Conchas and Utelakes, no deciduous trees or saltcedars werepresent (Conchas Lake, San Miguel County;Ute Lake, Quay County); however, between thelakes, a continuous stand of saltcedar and a fewlarge stands of cottonwoods were observed(San Miguel County). Near Logan, I observedpatches of saltcedar and a few single cotton-woods (1 km S Logan on US Highway 54, QuayCounty). Because squirrels were not observedat these localities and because wooded ripariancorridors were patchy along some eastern sec-tions of the Canadian River in New Mexico, itseems unlikely that this river provided a corri-dor for eastern fox squirrels to disperse fromTexas to Raton, New Mexico.

Next, I examined 3 areas along the Purga-toire River in southeastern Colorado for pop-ulations of S. niger and for a dispersal routefrom Colorado to Raton. The Purgatoire Riverflows 34 km N of Raton through Trinidad, LasAnimas County, Colorado. The river is a trib-utary of the Arkansas River, which eventuallyflows into Kansas (Fig. 1). Eastern fox squirrels


have been known near the Arkansas River inHamilton County, Kansas since at least 1959(Hall and Kelson, 1959; Fig. 1), and this loca-tion is 40 km east of the border of Coloradoand Kansas.

On 16 December 2000, I observed 8 S. nigerin Trinidad, Colorado: 2 in a residential areanear Trinidad State Junior College and 6 in KitCarson Park. I then searched for squirrelsalong the Purgatoire River from Trinidad tothe intersection of CO Highway 350. AlthoughI did not observe S. niger, this 20-km stretch ofriver had a wide and continuous stand of ma-ture cottonwoods and other deciduous trees.Next, I searched for squirrels from the junc-tion of CO Highway 109 and the PurgatoireRiver to a point 10.5 km SW of this site. I ob-served many scattered groups of cottonwoodswithin a fairly continuous band of saltcedars.In 1 large group of mature cottonwoods, I ob-served 2 adult S. niger (5.5 km SW junction ofCO Highway 109 and Purgatoire River, OteroCounty; Fig. 1; Appendix 1). In addition to myobservations along the river, an additional S.niger was observed in cottonwoods adjacent toa dense stand of Russian-olive (Elaeagnus an-gustifolia) where CO Highway 101 crosses thePurgatoire River, 4 km south of Las Animas,Bent County (K. N. Geluso, in litt.; Fig. 1; Ap-pendix 1). Besides finding eastern fox squirrelsalong the Purgatoire River, I compiled 10 ad-ditional records of S. niger along the ArkansasRiver and another record along one of its trib-utaries (Fountain Creek, El Paso County; Fig.1; Appendix 1). Above, I have included all con-spicuous woody vegetation observed along riv-ers. Although it is unlikely that S. niger lives instands of saltcedars, the possibility exists thatsquirrels might periodically move throughthem to reach habitats that are more favorable.

From these observations of eastern fox squir-rels along the Arkansas River and its tributariesin southeastern Colorado, S. niger is clearly es-tablished throughout the Arkansas watershedeast of the mountain front. Although S. nigerwas not indigenous to Colorado in the early1900s (Cary, 1911) and many human introduc-tions have been documented (Hoover and Yea-ger, 1953; Armstrong, 1972; Fitzgerald et al.,1994; Appendix 1; Fig. 1), I agree with Arms-trong (1972) that S. niger should be considereda member of the native fauna of Colorado be-cause of its natural westward movement into

the state. Because generally continuous corri-dors of woodland now connect natural popu-lations of S. niger in Kansas and Nebraska tomost towns east of the Rocky Mountains withknown introductions, I believe that most loca-tions with introductions of S. niger in easternColorado would have had native populationsof fox squirrels today, even if introductions hadnever occurred.

In addition, evidence suggests that S. niger inRaton, New Mexico, might be the result of nat-ural colonization. Raton lies 34 km south ofTrinidad and, although these cities are sepa-rated by a 2,390-m pass, they are nearly con-nected by a narrow corridor of riparian wood-land on both sides of the pass (i.e., RailroadCanyon in Colorado and Raton Creek in NewMexico). To date, there are 2 published ex-amples of S. niger expanding into montanefoothills of Colorado. Fitzgerald et al. (1994)reported that S. niger has penetrated the foot-hills near Evergreen, Jefferson County, Colo-rado by following riparian corridors up to2,285 m, and Hoover and Yeager (1953) de-scribed the gradual colonization of fox squir-rels to elevations of 2,380 m along BuckhornCreek, Larimer County, Colorado (32 km W ofFort Collins). Available information suggeststhat eastern fox squirrels might not have beenintroduced into Raton by human agency, andit seems there was ample opportunity for thesquirrels to reach Raton by natural coloniza-tion via corridors of riparian woodland.

I thank Z. Yaksich of Raton for photographs ofeastern fox squirrels in her yard. I thank D. M. Arms-trong, M. A. Bogan, E. W. Valdez, and 2 anonymousreviewers for helpful suggestions on earlier versionsof this manuscript. I thank the following museumpersonnel for their efforts in searching for recordsof eastern fox squirrels: W. G. Alther and C. A.Jones, Denver Museum of Nature & Science; C. A.Ramotnik, Biological Survey Collection, Museum ofSouthwestern Biology, University of New Mexico, Al-buquerque; B. D. Patterson, The Field Museum, Chi-cago; R. L. Humphrey, University of Colorado Mu-seum (UCM), Boulder; J. Clarke and J. Johnson,University of Northern Colorado, Greeley; and T. Pa-checo, American Museum of Natural History, NewYork. I thank A. S. Fox for preparing Fig. 1 and J.Salazar-Bravo for translating the abstract into Span-ish.

March 2004 115Notes

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CAIRE, W., J. D. TYLER, B. P. GLASS, AND M. A. MARES.1989. Mammals of Oklahoma. University ofOklahoma Press, Norman.

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FREY, J. K., AND M. L. CAMPBELL. 1997. Introducedpopulations of fox squirrels (Sciurus niger) in theTrans-Pecos and Llano Estacado regions of NewMexico and Texas. Southwestern Naturalist 42:356–358.

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HOFFMANN, R. S., P. L. WRIGHT, AND F. E. NEWBY.1969. The distribution of some mammals in Mon-tana. I. Mammals other than bats. Journal ofMammalogy 50:579–604.

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JOHNSON, W. C. 1994. Woodland expansion in thePlatte River, Nebraska: patterns and causes. Eco-logical Monographs 64:45–84.

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KNAPP, S. J., AND J. E. SWENSON. 1986. New rangerecords for the fox squirrel in the YellowstoneRiver drainage, Montana. Prairie Naturalist 18:128.

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SPARKS, D. W., AND J. R. CHOATE. 2000. Distribution,natural history, conservation status, and bioge-ography of bats in Kansas. In: Choate, J. R., edi-tor. Reflections of a naturalist: papers honoringProfessor Eugene D. Fleharty. Fort Hays Studies,Special Issue 1:173–228.

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Submitted 8 January 2002. Accepted 28 April 2003.Associate Editor was Cheri A. Jones.

APPENDIX 1 New records for eastern fox squirrel(Sciurus niger) in northeastern New Mexico andsoutheastern Colorado.


NEW MEXICO: COLFAX COUNTY: Raton, nearMount Calvary Cemetery and Raton High School(sighting by K. Geluso, 5 September 1999); Raton,Colfax County Courthouse (sighting by K. Geluso,16 December 2000); Raton, residential areas (sigh-tings and photographs by Z. Yaksich since 1998,pers. comm.; sightings by B. K. Yaksich since 2000,pers. comm.).

COLORADO: BACA COUNTY: Two Buttes WildlifeManagement Area (sightings and documentation ofintroduction in 1978 by M. Elkins, in litt.). BENT

COUNTY: Fort Lyon, Veterans Administration MedicalCenter (sighting by K. N. Geluso, 18 May 2001, inlitt.); Las Animas, Vigil Avenue and 6th Street (sight-ing by K. N. Geluso, 18 October 2001, in litt.); Junc-tion of Purgatoire River and CO Highway (Hwy)101, 4 km S Las Animas (sighting by K. N. Geluso,20 March 2001, in litt.). EL PASO COUNTY: Fountain

Creek Nature Center (sightings by J. E. Hunter sinceat least the 1980s, pers. comm.). FREMONT COUNTY:Florence (sightings by E. W. Valdez since the 1980s,pers. comm.); Canon City (sightings by E. W. Valdezsince the 1980s, pers. comm.). LAS ANIMAS COUNTY:Trinidad, near Trinidad State Junior College and inKit Carson Park (sightings by K. Geluso, 16 Decem-ber 2000). OTERO COUNTY: 0.25 mi W Manzanola(University of Colorado Museum, Boulder, UCM#11917); Rocky Ford (sighting by K. Geluso in the1990s); La Junta (sightings by D. A. Leatherman, inlitt.); 1 mi NE La Junta (UCM #11892); Bent’s OldFort National Historic Site (S. niger listed on faunallist, in litt.); 5.5 km SW junction of CO Hwy 109 andPurgatoire River (sighting by K. Geluso, 22 April2001). PROWERS COUNTY: Lamar, Willow Creek Park(sightings by K. N. Geluso, 20 March 2001, in litt.).PUEBLO COUNTY: Pueblo (sightings by E. W. Valdezsince the 1980s, pers. comm.).

SPATIAL PATTERNS AND DYNAMIC INTERACTIONS AMONGRACCOONS IN EASTERN KANSAS

STANLEY D. GEHRT* AND LLOYD B. FOX

Department of Biological Sciences, Emporia State University, Emporia, KS 66801 (SDG)Kansas Department of Wildlife and Parks, Emporia, KS 66801 (LBF)

Present address of SDG: School of Natural Resources, Ohio State University, 210 Kottman Hall, 2021 Coffey Road,Columbus, OH 43210-1095

*Correspondent: [email protected]

ABSTRACT We report on intrasexual spatial patterns and dynamic interactions of northern rac-coons in eastern Kansas. In general, extensive spatial overlap occurred among female and maledyads in each season and among age classes. The dynamic interaction test revealed positive inter-action among 5 of 9 male dyads, and no evidence of negative interaction. Some male dyads dennedand traveled together for intervals of varying lengths (2 to 16 days) in each season of the year.There was no evidence of dynamic interaction among female dyads. We provide additional evi-dence that social behavior of male raccoons exhibits geographic variation, and some level ofsociality might be more common than currently described for this species.

RESUMEN Informamos acerca de patrones espaciales intrasexuales e interacciones dinamicasde los mapaches en el este de Kansas. En general, una extensa superposicion espacial ocurrioentre pares de hembras y pares de machos en cada temporada y entre clases de edad. La pruebade la dinamica de la interaccion revelo una interaccion positiva entre 5 de 9 pares de machos, yninguna evidencia de una interaccion negativa. Algunos pares de machos se refugiaron y viajaronjuntos por intervalos de longitudes variadas (2 a 16 dıas) en cada estacion del ano. No huboevidencia de una interaccion dinamica entre pares de hembras. Proporcionamos evidencia adicio-nal de que la conducta social de mapaches machos exhibe variacion geografica, y algun nivel desocializacion puede ser mas comun que lo descrito hoy en dıa para esta especie.

The northern raccoon (Procyon lotor) gener-ally is considered to be solitary, with the excep-tion of mothers and dependent offspring(Ewer, 1973; Barash, 1974; Wilson, 1975; Kauf-

mann, 1982; Sandell, 1989). Previous workerstypically have described space use by raccoonsas overlapping home ranges with little inter-action between individuals, or as local territo-

March 2004 117Notes

riality (Stuewer, 1943; Mech et al., 1966; John-son, 1970; Kaufmann, 1982). However, raccoonsocial behavior might be more complex thanpreviously understood, particularly amongmales. For example, males in North Dakota ex-hibited intrasexual territoriality with active ter-ritorial defense (Fritzell, 1978). Elsewhere,males have overlapping home ranges but canexhibit local territoriality or other forms of in-tolerance toward conspecifics (Tevis, 1947;Johnson, 1970). Gehrt and Fritzell (1998a) re-ported adult males in southern Texas that oc-curred in distinct spatial groups, within whichmales denned and traveled with group mem-bers throughout most of the year. Recently,similar behavior was reported for males in Mis-sissippi (Chamberlain and Leopold, 2002).This type of social system, in which females aresolitary and males form social groups, is rareamong carnivores, and how common it is with-in raccoon populations is uncertain. Thus, thefull range of social behavior expressed by rac-coons, and solitary carnivores, might not yet bedescribed. We report on spatial patternsamong adults and dynamic interactions ob-served during a radiotelemetry study of rac-coons in eastern Kansas, with a particular em-phasis on adult males.

Our study was originally designed to addressquestions regarding population ecology forraccoons in eastern Kansas, not specifically so-cial behavior. However, in this paper we rean-alyze data with a dynamic interaction test(Doncaster, 1990), developed following ourfieldwork, which can be used to elucidate as-sociations between individuals by using simul-taneous radiotelemetry locations. Doncaster’s(1990) test is a particularly useful tool for de-scribing social behavior of solitary, nocturnalspecies, such as raccoons.

The study area (ca. 900 ha), comprised pri-marily of small farms, was located in rural LyonCounty, Kansas. Land use within the study areawas 51% cropland, 21% woodland, 18% grass-land, 7% old-field or brush, and 3% wetland.The Neosho River meanders through the cen-ter of the study area, and most of our trappingand telemetry efforts were focused along theriver. The area was subjected to hunting, trap-ping, and hunting with hounds during the fur-bearer season, and to experimental houndingduring the closed season.

We conducted livetrapping primarily during

spring and autumn of each year from 1985through 1987 and radiotelemetry from 1985through 1989. Wire-mesh, box livetraps wereplaced in wooded or riparian habitats, usuallynear logs or at the base of trees, to maximizetrapping success. Upon capture, raccoons wereimmobilized with an intramuscular injection ofketamine hydrochloride (Bigler and Hoff,1974), and we subsequently determined thesex, estimated age via tooth wear (Grau et al.,1970), and ear-tagged each individual. Rac-coons .12 months of age were consideredadults.

A subsample of adults was fitted with radio-collars (Advanced Telemetry Systems, Inc.,Isanti, Minnesota). Radiocollared raccoonswere located from August 1985 to May 1986,from September 1986 to May 1987, and fromJune 1988 to March 1989. We estimated loca-tions by triangulation from designated sitesalong roads or by approaching on foot with ahand-held antenna and receiver. Bearings wereplotted on United States Geological Survey 7.5-minute topographic maps with UniversalTransverse Mercator coordinates. Locations ofactive raccoons tracked at night usually weretriangulated, with 5 to 7 min elapsing betweenthe first and third bearing for each individual.Occasionally, raccoons were seen during track-ing shifts, or raccoons were located in areaswhere only 2 bearings were possible.

Our protocol was to obtain 2 to 3 diurnallocations per week for all radiocollared rac-coons; however, our monitoring schedule wasaffected by extensive flooding during the au-tumn each year. Most roads were impassableduring and immediately following floods,which restricted our monitoring effort.

Raccoons with home ranges located near thecenter of the study area were located at nightat intervals of 60 to 90 min during 4-h to 6-hshifts. This time interval was sufficient for bi-ological independence between locations(Gehrt and Fritzell, 1997). Attempts to achievestatistical independence (Swihart and Slade,1985) between locations by increasing time in-tervals failed to reduce autocorrelation and re-moved biologically important data. Raccoonswith home ranges located on the edges of thestudy area were monitored opportunistically,usually 1 to 3 times during a tracking shift. Te-lemetry monitoring was limited to diurnal lo-cations during the 1988 and 1989 field season.


We partitioned telemetry data by seasonbased on biological and climatic criteria.Spring (February through March) correspond-ed to the mating period, summer ( Junethrough August) to litter-rearing and warmtemperatures, and autumn (Septemberthrough November) to the independence ofyoung and availability of autumn fruits andcrops; winter (December through January)typically inhibited raccoon movements and ac-tivity due to weather (Stains, 1956). We esti-mated the size and overlap of seasonal homeranges by calculating minimum convex poly-gons of raccoons with $20 locations. Spatialoverlap between 2 neighboring raccoons wasdetermined by modifying the ‘simple ratio’ ofGinsberg and Young (1992). This entailed di-viding the total number of locations of bothraccoons located within the overlap zone withthe total number of locations recorded forboth raccoons during the season, and multi-plying the result by 100 (Gehrt and Fritzell,1998a). Spatial overlap indices were comparedamong seasons with ANOVA.

For those pairs of raccoons (dyads) moni-tored simultaneously and exhibiting spatialoverlap, we used a nonparametric dynamic in-teraction test (Doncaster, 1990) to determineif pairs exhibited positive or negative interac-tion. The test constructs a frequency distribu-tion for distance intervals separating pairs oflocations that would be expected if animalswere moving independently of each other. Abinomial test was used to determine whetherthe observed frequency of simultaneous loca-tions separated by a critical distance was great-er (positive interaction) or less (negative inter-action) than the expected frequency (Doncas-ter, 1990). We used the following criteria forthe dynamic interaction test: 100 m for a crit-ical distance for both activity periods (this dis-tance interval encompassed our estimated te-lemetry error), 30 min as a simultaneous timeinterval for nocturnal locations, and 2 h for asimultaneous time interval for diurnal loca-tions if both raccoons were inactive. We con-structed distributions for each dyad separatelyfor diurnal and nocturnal data because of dif-fering temporal criteria and subsequentlypooled comparisons among activity periods toincrease sample sizes. In no instance did pat-terns differ between activity periods prior topooling for each dyad.

We captured 84 raccoons during trappingfrom 1985 through 1987, of which 31 (20 F, 11M) adults were radiocollared. The mean num-ber of locations obtained for each raccoon was83 (range 3 to 238), and 18 individuals (11 F,7 M) were located $20 times. Our telemetrywork was affected by a canine distemper epi-zootic in 1985, when many raccoons died soonafter they were radiocollared, and by extensiveflooding in 1985 and 1986. As a result of dis-temper, the population declined from an eco-logical density of 9.8 raccoons/km2 during au-tumn 1985 to 4.4 raccoons/km2 in 1987(Gehrt, 1988).

Mean (6 SD) home range size for femalesranged from a low of 19 6 16 ha (n 5 5) dur-ing winter to a high of 68 6 19 ha (n 5 6)during autumn. Mean spatial overlap differed(F3,24 5 5.36, P 5 0.006) among seasons. Spa-tial overlap in autumn (mean 5 60 6 22%, n5 24) was greater (P , 0.05) than that in win-ter (mean 5 36 6 30%, n 5 8), otherwise over-lap indices were similar among seasons. Spring(n 5 8) and summer (n 5 8) seasons each hada mean spatial overlap index of 50% (6 24spring, 6 31 summer).

Dynamic interaction tests were conductedfor 4 female dyads with spatial overlap indicesranging from 50 to 79 during autumn andspring, and with 24 to 115 simultaneous loca-tions per dyad. No dynamic interactions wereobserved for any of these dyads, in which ob-served frequencies (7 to 12%) of simultaneouslocations within the critical distance were notdifferent (P . 0.1) from expected frequencies.

Mean home range size for males rangedfrom a low of 60 6 35 ha (n 5 6) during au-tumn to a high of 163 6 15 ha (n 5 2) duringsummer. In general, extensive spatial overlapoccurred between members of male dyads ineach season and age class (Table 1). Mean spa-tial overlap differed (F2,14 5 4.54, P 5 0.03)among seasons. Spatial overlap in autumn(mean 5 81 6 3%, n 5 9) was greater (P ,0.05) than that in winter (mean 5 59 6 19%,n 5 4). Summer data were not compared toother seasons because of small sample size.Two males exhibited spatial overlap with dif-ferent males in subsequent years. For example,male 250 initially overlapped home ranges of3 males during autumn 1986, but he eventuallymoved to another portion of the study areaand maintained a home range exclusive of the

March 2004 119Notes

TABLE 1—Indices of spatial overlap for pairs of adult male raccoons (dyads) in eastern Kansas. Age classwas determined by tooth wear (Grau et al., 1970).

Dyad

A B

Age classa

A B Year Autumn Winter Spring Summer

17551678173817381738

16781738327227250

IIIIIVIVIV

IIIVIIIIII

19851985

1986–871986–871986–87

7983888278

81380

88550

327227327250

227250250790

IIIIIIII

IIIIIIII

1986–871986–871986–87

1988

83778080

68494

79470

93

a II 5 15–38 months; IV 5 58–86 months.

TABLE 2—Dynamic interaction tests (Doncaster, 1990) for pairs of radiocollared male raccoons (dyads)monitored in eastern Kansas, 1985 through 1988. Interval is month and year. N is the number of pairs ofsimultaneous locations recorded during the monitoring interval. Positive interaction is indicated when ob-served is greater than expected, and negative interaction is when the opposite is true.

Dyad

A B Interval N

Proportion withincritical distance

Observed Expected P

17551678173817381738

16781738327227250

9/85 to 10/8510/85 to 11/859/86 to 4/879/86 to 4/879/86 to 4/87

912

1118761

0.330.250.430.200.05

0.120.180.100.080.03

0.0890.408

,0.0001,0.0001

0.789327227327250

227250250790

9/86 to 4/879/86 to 4/879/86 to 4/876/88 to 11/88

87626362

0.380.210.060.34

0.140.060.030.06

,0.0001,0.0001

0.310,0.0001

original group of males. However, the newhome range of this male extensively over-lapped the home range of another male (790)in 1988 (Table 1).

The dynamic interaction test revealed signif-icant, positive interactions among 5 of 9 maledyads, and no evidence of negative interactions(Table 2). Male raccoons with positive dynamicinteraction traveled and denned together forintervals of varying lengths (2 to 16 days) ineach season of the year. The limited data re-corded during 1985 due to canine distemperprobably precluded statistically significant testsfor dyads examined at that time. Nevertheless,there was a consistent trend for higher ob-served frequencies of locations within the crit-ical distance than expected frequencies.

Extensive spatial overlap of seasonal homeranges occurred among female dyads duringeach season except winter. The winter declinein spatial overlap was probably a function ofreduced movement rather than intoleranceamong neighbors. Although they shared spaceand occasionally shared dens (Gehrt et al.,1990), females appeared to move indepen-dently of other females. This spatial pattern offemales was consistent with that reported inother studies. Gehrt and Fritzell (1998a)showed that spatial patterns of female rac-coons were affected by distributions of resourc-es in southern Texas, although occasionally fe-males would interact with other females andden communally.

The spatial patterns and dynamic interac-


tions exhibited by males in our study indicatedthat some male raccoons form temporary as-sociations characterized by traveling and den-ning together, and this behavior was exhibitedto some degree in all seasons. The results ofthe dynamic interaction test were consistentwith field observations. Although males wereapproached on foot infrequently during themonitoring period, it was not uncommon toobserve males denning simultaneously in thesame tree (Gehrt et al., 1990) or other restingsite. We also observed radiocollared malessharing den trees with unmarked raccoons.

Although the study area was subjected to in-tense flooding during autumn, it is unlikelythis affected the spatial distribution of rac-coons in our study. Major inundation usuallylasted a few days, with waters receding frommost of the study area within a couple weeks.As water receded, access to the area remainedproblematic for monitoring because mostroads (which were dirt or clay) on the areawere impassable, but raccoons could, and did,move across the area. Thus, most of our datafor those seasons were recorded well afterfloodwaters had receded, and raccoons hadbeen mobile for weeks.

Degrees of relatedness between males wereunknown, but not all dyads could have beencomposed of littermates given the discrepan-cies in age within some dyads. Also, male rac-coons typically undergo natal dispersal (Gehrtand Fritzell, 1998b), making it unlikely thatadult males are closely related, although it ispossible that some littermates might dispersetogether. The benefits of these male associa-tions are unclear, but might be, in part, relatedto access to females for future mating oppor-tunities (Gehrt and Fritzell, 1998a). The distri-bution of females, and competition for matingopportunities, has been proposed as an expla-nation for male coalitions in other solitary car-nivores, such as cheetahs (Acinonyx jubatus;Caro, 1994) and slender mongooses (Galerellasanguinea; Rood, 1989; Waser et al., 1994).

Not all members of the population were ra-diocollared, so it was not possible to determinethe overall spatial pattern and extent of dy-namic interactions for the population. How-ever, evidence from trapping data, combinedwith locations from other radiocollared males(with insufficient data to estimate home rang-es), indicated that spatial overlap occurred to

a greater extent than reported here (Gehrt,1988). Thus, dynamic interactions amongadult males in our population also might beunderrepresented.

The dynamic interaction in our study is sim-ilar to male associations described for raccoonsin southern Texas (Gehrt and Fritzell, 1998a);however, in that study, males occurred in spa-tially distinct groups with little overlap betweengroups. We did not observe spatial groups inour study, if they occurred, possibly due tosmall sample sizes, to the distribution of radio-collars in the population, or to the canine dis-temper epizootic, which removed a large por-tion of the population at the beginning of thestudy. Data for radiocollared females did notindicate that they occurred in spatial groups,but that they exhibited spatial overlap through-out the study area (Gehrt, 1988). The patternswe observed were similar to those of raccoonsin Mississippi, where males exhibited associa-tions but not distinct groups (Chamberlainand Leopold, 2002).

Many species of carnivores with broad nichesexhibit gradations in social systems (Macdon-ald, 1983). Results from our study provide ad-ditional evidence that social behavior of rac-coons might vary geographically, and suggestthat positive associations among male raccoonsmight be more prevalent than indicated by thecurrent literature.

We thank the various landowners for access to theirproperties. Our study was supported by the Kansas De-partment of Wildlife and Parks (formerly Kansas Fishand Game Commission) and by Emporia State Univer-sity. C. McCullough, D. Blew, and J. Gehrt assisted withfieldwork. S. Gehrt completed the manuscript whilesupported by the Max McGraw Wildlife Foundation.We thank J. Rizzo for the Spanish translation.

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Submitted 16 April 2002. Accepted 26 March 2003.Associate Editor was Cheri A. Jones.

predation by gray catbird on brown … by gray catbird on brown thrasher eggs james w. rivers* and...

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