barred owls eating worms and slugs: the advantage in not being picky eaters

Barred Owls Eating Worms and Slugs: The Advantage in Not Being Picky EatersAuthor(s): Kent B. Livezey, Mark F. Elderkin, Peter A. Cott, Jared Hobbs and John P. HudsonSource: Northwestern Naturalist, Vol. 89, No. 3 (Winter, 2008), pp. 185-190Published by: Society for Northwestern Vertebrate BiologyStable URL: http://www.jstor.org/stable/30135134 .

Accessed: 09/06/2014 20:04

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

Society for Northwestern Vertebrate Biology is collaborating with JSTOR to digitize, preserve and extendaccess to Northwestern Naturalist.

http://www.jstor.org

This content downloaded from 195.78.109.156 on Mon, 9 Jun 2014 20:04:55 PMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=snwvb

http://www.jstor.org/stable/30135134?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


GENERAL NOTES WINTER 2008

deepwater dogfishes from southeastern Australia [dissertation]. Warrnambool, Australia: Deacon University. 238 p.

JONES AA, WHITE WT, POTTER IC. 2005. A hermaph- roditic Port Jackson shark, Heterodontus portus- jacksoni, with complete and separate female and male reproductive tracts. Journal of the Marine Biological Association of the United Kingdom 85: 1171-1172.

KING AD. 1966. Hermaphroditism in the common dogfish (Scyliorhinus canicula). Journal of Zoology 148:312-314.

MATTA ME. 2006. Aspects of the life history of the Alas- ka skate, Bathyraja parmifera, in the eastern Bering Sea [thesis]. University of Washington. 92 p.

MCEACHRAN JD, ASCHLIMAN N. 2004. Phylogeny of Batoidea. In: Carrier JC, Musick JA, Heithaus MR, editors. Biology of sharks and their relatives. Boca Raton: CRC Press. p 79-113.

ORMSETH O, MATTA B. 2007. Gulf of Alaska skates. In: Stock assessment and fishery evaluation report for the groundfish resources of the Gulf of Alaska for 2008. Anchorage, AK: North Pacific Fishery Management Council. Appendix B, Chapter 17. p 957-1008.

QUIGNARD JP, CAPAPE C. 1972. Cas d'hermaphrodisme chez Raja miraletus L. 1758. Travaux du Laboratoire de Biologie Halieutique, Universite Rennes 6:133- 140.

SCENNA LB, DIAZ DE ASTARLOA JM, COUSSEAU MB. 2007. Abnormal hermaphroditism in the multi- spine skate Bathyraja multispinis (Chondrichthyes, Rajidae). Journal of Fish Biology 71:1232-1237.

STEVENSON DE, ORR JW, HOFF GR, MCEACHRAN JD. 2007. Field guide to sharks, skates, and ratfish of Alaska. Fairbanks, AK: Alaska Sea Grant College Program, University of Alaska Fairbanks. 77 p.

STEVENSON DE, ORR JW, HOFF GR, MCEACHRAN JD. 2008. Emerging patterns of species richness, di- versity, population density, and distribution in the skates (Rajidae) of Alaska. Fishery Bulletin 106:24-39.

TEMPLEMAN W. 1987. Differences in sexual maturity and related characteristics between populations of thorny skate (Raja radiata) in the northwest At- lantic. Journal of Northwest Atlantic Fishery Sci- ence 7:155-167.

VERISSIMO, A, GORDO L, FIGUEIREDO I. 2003. Reproduc- tive biology and embryonic development of Cen- troscymnus coelolepis in Portuguese mainland waters. ICES Journal of Marine Science 60:1335-1341.

Pacific Shark Research Center, Moss Landing Ma- rine Laboratories, 8272 Moss Landing Rd., Moss

Landing, CA 95039 (DLH [email protected].

edu, DAE). Submitted 26 September 2007, accepted

12 June 2008, Corresponding Editor: JW Orr.

NORTHWESTERN NATURALIST 89:185-190 WINTER 2008

BARRED OWLS EATING WORMS AND SLUGS: THE ADVANTAGE IN NOT BEING PICKY EATERS

KENT B LIVEZEY, MARK F ELDERKIN, PETER A COTT, JARED HOBBS, AND JOHN P HUDSON

Key words: Barred Owl, Strix varia, Northern Spotted Owl, Strix occidentalis caurina, prey, earthworms, slugs

The Barred Owl (Strix varia) recently expanded its range from eastern to western North America and now occurs throughout the range of the Northern Spotted Owl (Strix occidentalis caurina; hereafter Spotted Owl). The Spotted Owl was listed as federally endangered in Canada (Camp- bell and Campbell 1984; Government of Canada 2002) and federally threatened in the United States (US Fish and Wildlife Service 1990) due primarily to loss of its habitat-mature and old-

growth forest. Now the larger, more aggressive Barred Owl appears to be negatively affecting Spotted Owl site occupancy (Kelly and others 2003; Pearson and Livezey 2003; Gremel 2005; O1- son and others 2005; Hamer and others 2007), reproduction (Olson and others 2004), and survival (Anthony and others 2006). Throughout their range, Spotted Owl populations have been de- clining at approximately 3.7% annually from 1985 to 2003, and these declines are most pro- nounced in the northern part of its range where Barred Owls have been present the longest (An- thony and others 2006). In Gifford Pinchot Na- tional Forest, Washington, Barred Owls outnum-

185



186 NORTHWESTERN NATURALIST 89(3)

ber Spotted Owls in reserves set aside for Spotted Owl conservation (Pearson and Livezey 2003, 2007), thereby calling into question whether the management strategies presented in the North- west Forest Plan (USDA and USDI 1994) can re- cover Spotted Owls. Here we add insight into a facet of this apparent competition by providing the 1st published direct observations of Barred Owls preying on earthworms (Annelids; Oligo- chaeta) and slugs (Molluscs: Gastropods: Stylom- matophora), and discuss the ramifications of the use of such innocuous prey by Barred Owls on the future of Spotted Owls.

Observations of Earthworm Predation

From 1985 to 1986, MFE studied the breeding and feeding ecology of a population of Barred Owls in the fragmented agricultural landscape of the Annapolis Valley, Nova Scotia (decimal degrees (DD) 45.0866 N, -64.44553 W; Elderkin 1987). Forests in his study area comprised primarily Red Spruce (Picea rubens), White Pine (Pinus strobes), Sugar Maple (Acer saccharum), and Yellow Birch (Betula alleghan- iensis). In addition to typical methods to determine prey by finding prey remains at nests (n = 740), prey remains in pellets (n = 635), and intact prey at nests (n = 105), MFE documented by camera the parental deliveries of prey to nestlings in a nest box. Of the 178 prey identified by camera, 64 (27.6%) were earthworms. MFE frequently observed Barred Owls hunting for and capturing worms on the forest floor and on roads during rainy nights. This activity was most common in May when the owls were also feeding on frogs and salamanders traveling to wetlands and roadside ditches to breed.

From 10:00 to 14:00 on 27 March 1999, JH observed a female Barred Owl in a mixed conif- erous forest in southern British Columbia (DD 49.5383 N, -122.5558 W) preying on earthworms. The owl was in a forest stand domi- nated by mature ( 150-y-old) Douglas-fir (Pseudotsuga menziesii) with a mixed understory of Arbutus (Arbutus menziesii) and Bigleaf Ma- ple (Acer macrophyllum). The owl's hunting perch was a branch 7 m up in a Douglas-fir tree. She periodically cocked her head side to side for about 30 s as if listening for prey, flew to the ground within about a 10-m radius of the tree, flipped over some leaves with her beak, caught and ate an earthworm, then flew back to her branch. She caught a total of 7 earthworms and

1 salamander in this manner within approximately 2 h. JH had habituated the owl to his presence by being close to her for several hours each day for 15 d before this observation. He was 5 to 7 m from the base of the owl's perch during this time and identified the caught prey with the aid of 10-power binoculars.

At 06:30 on 30 August 2003, JPH observed from his vehicle a Barred Owl flying from its perch on a utility pole and landing on a driveway near Ju- neau, Alaska. Forests dominating the area con- sisted of old-growth and young-growth stands of Western Hemlock (Tsuga heterophylla) and Sitka Spruce (Picea sitchensis) with stands of Red Alder (Alnus rubra) in recently disturbed areas. The observation occurred within 200 m of a peat bog with scattered stunted Shore Pine (Pinus contorts contorts). He backed-up his vehicle to within 7 m of the owl as it was feeding on something. He got out of his vehicle and approached the owl, which then flew to a nearby fence post. On the ground where the owl had been feeding was half of a large earthworm next to a talon mark in the dirt.

Observation of Slug Predation

From 06:30 to 07:00 on 6 May 2006, PAC observed a Barred Owl foraging in Lewis Meadow near the Hoh River in Olympic National Park, Washington (DD 47.8789N, -123.7378W). The meadow was approximately 1 ha in size and was bordered by old-growth forest comprising primarily Western Hemlock and Western Red- cedar (Thuja plicata). Herds of Roosevelt Elk (Cervus canadensis roosevelti) frequented the area to graze, resulting in short, cropped grass and little ground cover. The owl landed on the ground and foraged in the grass, using its beak to move vegetation in the manner of a Spotted Towhee (Pipilo maculates). PAC observed the owl

capturing and eating 2 black slugs approximately 15 cm in length. These slugs probably were Black Anion Slugs (Anion rufus; species per T Pearce, Carnegie Museum of Natural History, Pittsburgh, PA, pens. comm. and W Leonard, Washington Department of Transportation, Olympia, WA, pens. comm.; common name per Turgeon and others 1998). The owl held each slug with its beak, paused for a moment, and then swallowed it whole. PAC used 10-power binoculars and was 30 to 100 m from the owl at all times. There were approximately 12 Ameri- can Robins (Turdus migratorius) foraging in the



GENERAL NOTES

meadow as well, some only a few meters away from the owl.

Few animals in the Pacific Northwest prey on slugs. These include the Masked Shrew (Sorex cinereus; Allen 2004), the Shrew-mole (Neurotri- chus gibbsi; Richter 1980), gartersnakes (Tham- nophis elegans, T. ordinoides, T. sirtalis; Arnold 1981; Brown and others 1995), and the Sharp- tail Snake (Contia tenuis) which feeds almost ex- clusively on slugs (Brown and others 1995). The slime and sticky caudal mucous of slugs have been shown during tests to cause shrews and predaceous ground beetles (Carabus spp.) to abort predation attempts (Richter 1980).

Difference in Use of Soft-bodied Prey by Barred vs. Spotted Owls and Possible Implications for Spotted Owls

Barred Owls eat a much wider variety of prey than do Spotted Owls (Hamer and others 2001). The only study comparing food habits of sympatric Spotted and Barred owls found that Barred Owl prey (n = 265) was 76.1% mammals, 11.0% birds, 5.7% amphibians, 3.8% insects, 2.6% fish, and 0.8% (n = 2) snails; where- as Spotted Owl prey (n = 296) was 96.2% mammals, 2.8% birds, and 1.0% insects (Hamer and others 2001). In the largest prey study of Spot- ted Owls (Forsman and others 2004), identified prey items (n = 24,497) were 91.5% mammals, 4.3% birds, 4.1% insects, and less than 0.1% other prey which included 2 lizards, 2 snails, 1 crayfish, 1 scorpion, and 1 snake.

The studies of Hamer and others (2001) and Forsman and others (2004) used only pellet analysis, which is true for the vast majority of studies that document prey for Barred and Spotted owls. Pellet analysis under-detects soft-bodied prey including earthworms and slugs that have no hair, bones, teeth, feathers, shells, or conspicuous chitinous material (Yom- Tov and Wool 1997; Marchesi and others 2002). This under-detection of soft-bodied prey (as well as the more-varied diet of Barred Owls compared to Spotted Owls) was shown in a synthesis of 43 Barred Owl prey studies docu- menting 7077 individual prey items (Livezey 2007). In that synthesis, Barred Owl prey ob- tained from pellets (n = 5504) were mammals (74.7%); birds (8.3%); amphibians (6.4%); insects and spiders (5.6%); crayfish (3.0%); fish (1.5%); reptiles, snails and slugs, and earthworms (<1.0% each). However, the distribution

of Barred Owl prey types documented by means other than pellets (observations, camera-documented food deliveries, intact prey at nest, prey remains at nest, prey in stomachs; n = 1573; Livezey 2007) was significantly differ- ent (X28 = 414.76, p < 0.001): mammals (62.0%);

birds (13.5%); insects and spiders (9.5%); amphibians (4.8%); earthworms (4.5%); fish (3.3%); reptiles (1.1%); crayfish (<1.0%); and snails and slugs (<1.0%). For simplicity, this synthesis grouped snails and slugs into 1 cat- egory and reported documentation that Barred Owls ate 16 of these gastropods (see Table 1 in Livezey 2007). Specifically, there were 9 snails in stomachs (7 in Kilham 1930; 2 in Fisher 1893), 5 snails in pellets (2 in Coon 1917; 2 in Hamer and others 2001; 1 in Elderkin 1987), the remains of 1 snail at a nest (Elderkin 1987), and 1 slug in a stomach (Kilham 1930). The 2 slugs observed by PAC were not included in Livezey 2007. Only 1 study documented prey deliveries by adult Barred Owls to nestlings using a mo- tion-activated camera mounted near a nest (Elderkin 1987), which probably yields data that are least biased toward the non-detection of soft-bodied prey. Of the 74 worms known to be preyed upon by Barred Owls, 64 were documented by this camera (Elderkin 1987), 8 by direct observation (JH, JPH; the 1 by JPH was not included in Livezey 2007), and only 2 by pellets (Elderkin 1987).

We did not attempt to conduct an exhaustive review of all publications and reports docu- menting Spotted Owl prey, but our cursory analysis found no evidence of Spotted Owls preying on worms or slugs in prey syntheses (Gutierrez and others 1995; Sztukowski and Courtney 2004), publications, reports, or theses (Barrows 1980, 1987; Solis 1983; Forsman and others 1984, 2004; Ward 1990; Cutler and Hays 1991; Bevis and others 1997; Rosenberg and others 2003). In addition, personal communi- cations with Spotted Owl researchers (R An- thony, U.S. Geological Survey, Corvallis, OR; E Forsman, U.S. Forest Service, Corvallis, OR; S Gremel, Olympic National Park, Port Angeles, WA; D Wiens, Oregon State University, Corval- lis, OR) offered no such evidence. Non-pellet prey data we found for Spotted Owls, which would have the best chances of detecting soft- bodied prey, were: 4 stomachs containing 31 crickets (Marshall 1941) and 1 stomach full of moths (E Forsman, pers. comm.); captures of 1

WINTER 2008 187



188 NORTHWESTERN NATURALIST

chipmunk (Tamias spp.) and an unidentified small animal and unsuccessful attempts to capture 4 chipmunks (Sovern and others 1994); an unsuccessful attempt to capture a Long-eared Chipmunk (Tamias quadrimaculatus; Laymon 1991); and captures (n = 2) and unsuccessful attempts to capture (n = 7) mice, squirrels, or birds (Forsman and others 1984).

We suggest that soft-bodied prey could ac- count for a large component of the diet of Barred Owls dependent on daily, seasonal, and annual availability of these and other food sources. For example, in MFE's study, earthworm prey deliveries to nestlings documented by camera increased during rainy days and nights. Also, pellets collected under roosts during rainy periods were unusual in that they were composed of ca- rabid beetle elytra (hard, protective outer wings), amphibian bones, and earthworm chaetae (stiff, paired hairs on each body segment) bound together in a thick exterior layer of mucus. Increased use of soft-bodied prey such as earthworms may be opportunistic with availability or may be seasonally selective if adults feed worms to very young nestlings to reduce potential hazards posed by ingesting bones, teeth, and feathers. Large annual proportions of Barred Owl diet and year-to-year variation in Barred Owl consumption have been shown for

another invertebrate, crayfish (Cambarus spp.), which, unlike earthworms and slugs, has an exoskeleton that is readily detectable in pellets; during a 20-y study, annual diet volume of crayfish averaged 3.4% and ranged from 0 to 31.1% (Korschgen and Stuart 1972).

Much additional effort would be required to detect soft-bodied prey in pellets. For earthworms, use of a dissecting microscope would be needed to detect chitinous chaetae. After exam- ining a few of these pellets microscopically, MFE discontinued this method due to the great time investment needed to at best determine presence or absence of worms. It is not possible to enu- merate the number of individual worms in each pellet due the large number of paired chaetae on each worm and the variation in numbers of seg- ments among worms. For Black Arion Slugs, a dissecting microscope or compound microscope would be needed to detect the "teeth" (radulae) and the calcium granules that compose their re- duced shell (T Pearce, pers. comm., and K Richter, King County Department of Natural Resources and Parks, Seattle, WA, pers. comm.). Unlike with

89(3)

earthworms, total number of slugs could be es- timated by these methods by counting sets of radulae.

Barred Owls not only overlap with Spotted Owls in their use of prey, but their diet includes a much wider variety of prey. Both of these behaviors may negatively affect Spotted Owls. Hamer and others (2001:226) found that the diets of these 2 species overlapped by 76% and concluded that this overlap "suggested that the two species may compete for food." Gutierrez and others (2007:189) predicted that "the Barred Owl will have negative impacts on the threatened Spotted Owl through competitive exclusion. Dietary relationships suggest that interference competition would ... be the mode of this relationship." Relative to Spotted Owls, the larger variety of prey used by Barred Owls probably allows them to more fully use available prey, take better advantage of daily and seasonal increases in prey availability, and be less influenced by fluctuations in small- mammal populations. It also probably permits them to occupy a less-restrictive distribution of forest types (Hamer and others 2007; Livezey 2007) and contributes to Barred Owls having smaller home ranges (Hamer and others 1989, 2007) and higher densities (Pearson and Live- zey 2007) than Spotted Owls. It is probable that many Spotted Owls have gone hungry while looking down on a stream full of fish, frogs, and crayfish, and on forest litter teaming with earthworms and slugs. Such prey are virtually or completely ignored by Spotted Owls but are readily eaten by Barred Owls.

Acknowledgments.-R Anthony, K Benkert, E Fors- man, S Gremel, J Hagans, W Leonard, B Livezey, C Machtans, T Pearce, K Richter, D Wiens, and an anonymous reviewer provided helpful information or review. C Lake and L Kivi reviewed preliminary drafts. KBL, MFE, PAC, JPH, and British Columbia Ministry of Environment funded page charges. US Fish and Wildlife Service partially funded the writ- ing of this note. The views expressed herein are those of the authors and are not necessarily those of the agencies or university for which they work.

LITERATURE CITED

ALLEN JA. 2004. Avian and mammalian predators of terrestrial gastropods. In GM Barker, editor. Nat- ural enemies of terrestrial molluscs. Oxfordshire, UK: CAB International Publishing. p. 1-36.

ANTHONY RG, FORSMAN ED, FRANKLIN AB, ANDER-

SON DR, BURNHAM KP, WHITE GC, SCHWARZ CJ,



GENERAL NOTES

NICHOLS J, HINES JE, OLSON GS AND 19 OTHERS. 2006. Status and trends in demography of North- ern Spotted Owls, 1985-2003. Wildlife Mono- graphs 163:1-48.

ARNOLD SJ. 1981. Behavioral variation in natural populations. II. The inheritance of a feeding re- sponse in crosses between geographic races of the garter snake, Thamnophis elegans. Evolution 35: 510-515.

BARROWS CW. 1980. Feeding ecology of the Spotted Owl in California. Journal of Raptor Research 14: 73-78.

BARROWS CW. 1987. Diet shifts in breeding and non- breeding Spotted Owls. Journal of Raptor Re- search 21:95-97.

BEVIS KR, RICHARDS JE, KING GM, HANSON EE. 1997. Food habits of the Northern Spotted Owl (Strix occidentalis caurina) at six nest sites in Washing- ton's East Cascades. In Duncan JR, Johnson DH, Nicholls TH, editors. Biology and Conservation of Owls of the Northern Hemisphere: Second In- ternational Symposium. Winnipeg, Manitoba, Canada. p. 68-73.

BROWN HA, BURY RB, DARDA DM, DILLER LV, PETER- SON CR, STORM RM. 1995. Reptiles of Washing- ton and Oregon. Storm RM, Leonard WP, coor- dinating editors. Seattle, WA: Seattle Audubon Society. 176 p.

CAMPBELL, EC AND RW CAMPBELL. 1984. Status report on Spotted Owl in Canada, 1983. Report to Committee on the Status of Endangered Wildlife in Canada. Ottawa, Ontario, Canada. 62 p.

COON WE. 1917. A note on the Barred Owl. Bird Lore 19:266-267.

CUTLER TL, HAYS DW. 1991. Food habits of Northern Spotted Owls in high elevation forests of Pelican Butte, southwestern Oregon. Northwestern Nat- uralist 72:66-69.

ELDERKIN ME 1987. The breeding and feeding ecology of a Barred Owl population in Kings County, Nova Scotia [thesis]. Wolfville, Nova Scotia: Aca- dia University. 203 p.

FISHER AK. 1893. The hawks and owls of the United States in their relation to agriculture. Washington, DC: USDA Division of Ornithology and Mam- malogy Bulletin No. 3. 210 p.

FORSMAN ED, MESLOW EC, WIGHT HM. 1984. Distri- bution and biology of the Spotted Owl in Oregon. Wildlife Monograph 87:1-64.

FORSMAN ED, ANTHONY RG, MESLOW EC, ZABEL CJ. 2004. Diets and foraging behavior of Northern Spotted Owls in Oregon. Journal of Raptor Re- search 38:214-230.

GOVERNMENT OF CANADA. 2002. Species at Risk Act. Government of Canada, Ottawa, Ontario, Canada.

GREMEL S. 2005. Factors controlling distribution and demography of northern spotted owls in a re-

served landscape [thesis]. Seattle, WA: University of Washington. 49 p.

GUTIERREZ RJ, FRANKLIN AB, LAHAYE WS. 1995. Spotted Owl. In: A Poole and F Gill, editors. Birds of North America No. 179. Philadelphia, PA: The Academy of Natural Sciences, and Washington, DC: The American Ornithologists' Union. 28 p.

GUTIERREZ RJ, CODY M, COURTNEY S, FRANKLIN AB. 2007. The invasion of Barred Owls and its potential effect on the Spotted Owl: a conservation co- nundrum. Biological Invasions 9:181-196.

HAMER TE, SEIM SG, DIXON KR. 1989. Northern Spotted Owl and Northern Barred Owl habitat use and home range size in Washington: preliminary report. Olympia, WA: Washington Depart- ment of Wildlife. 65 p.

HAMER,TE, HAYS DL, SENGER CM, FORSMAN ED. 2001. Diets of Northern Barred Owls and North- ern Spotted Owls in an area of sympatry. Journal of Raptor Research 35:221-227.

HAMER TE, FORSMAN ED, GLENN EM. 2007. Home range attributes and habitat selection of Barred Owls and Spotted Owls in an area of sympatry. Condor 109:750-768.

KELLY EG, FORSMAN ED, ANTHONY RG. 2003. Are Barred Owls displacing Spotted Owls? Condor 105:45-53.

KILHAM L. 1930. Stomach contents of Barred Owl. Auk 47:418.

KORSCHGEN LJ, STUART HB. 1972. Twenty years of avian predator-small mammal relationships in Missouri. Journal of Wildlife Management 36: 269-282.

LAYMON SA. 1991. Diurnal foraging by Spotted Owls. Wilson Bulletin 103:138-140.

LIVEZEY KB. 2007. Barred Owl habitat and prey: a review and synthesis of the literature. Journal of Raptor Research 41:177-201.

MARCHESI L, PEDRINI P, SERGIO F. 2002. Biases asso- ciated with diet study methods in the Eurasian Eagle-Owl. Journal of Raptor Research 36:11-16.

MARSHALL JT. 1941. Food and habitat of the Spotted Owl. Condor 44:66-67.

OLSON GS, GLENN EM, ANTHONY RG, FORSMAN ED, REID JA, LOSCHL PJ, RIPPLE WJ. 2004. Modeling demographic performance of Northern Spotted Owls relative to forest habitat in Oregon. Journal of Wildlife Management 68:1039-1053.

OLSON GS, ANTHONY RG, FORSMAN ED, ACKERS SH, LOSCHL PJ, REID JA, DUGGER KM, GLENN EM, RIP- PLE WJ. 2005. Modeling of site occupancy dynam- ics for Northern Spotted Owls, with emphasis on the effects of Barred Owls. Journal of Wildlife Management 69:918-932.

PEARSON RR, LIVEZEY KB. 2003. Distribution, numbers, and site characteristics of Spotted Owls and Barred Owls in the Cascade Mountains of Wash- ington. Journal of Raptor Research 37:265-276.

189 WINTER 2008



190 NORTHWESTERN NATURALIST

PEARSON RR, LIVEZEY KB. 2007. Spotted Owls, Barred Owls, and Late-Successional Reserves. Journal of Raptor Research 41:156-161.

RICHTER KO. 1980. Movement, reproduction, defense, and nutrition as functions of the caudal mucus in Ariolimax columbianus. Veliger 23:43-47.

ROSENBERG DK, SWINDLE KA, ANTHONY RG. 2003. Influence of prey abundance on Northern Spotted Owl reproductive success in western Oregon. Ca- nadian Journal of Zoology 81:1715-1725.

SOLIS DM. 1983. Summer habitat ecology of Spotted Owls in northwestern California [thesis]. Arcata, CA: Humboldt State University. 168 p.

SOVERN SG, FORSMAN ED, BISWELL BL, ROLPH DN, TAYLOR M. 1994. Diurnal behavior of the Spotted Owl in Washington. Condor 96:200-202.

SZTUKOWSKI L, COURTNEY S. 2004. Prey. In: S. Court-

ney, editor. Scientific evaluation of the status of the northern spotted owl. Portland, OR: Sustain- able Ecosystems Institute. p. 4-1-4-32.

TURGEON DD, QUINN JF JR., BOGAN AE, COAN EV,

HOCHBERG FG, LYONS WG, MIKKELSEN PM, NE-

VES RJ, ROPER CFE, ROSENBERG G, ROTH B, SCHEL-

TEMA A, THOMPSON FG, VECCHIONE M, WILLIAMS

JD. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: mollusks, second edition. Bethesda, MD: Ameri- can Fisheries Society Special Publication 26, American Fisheries Society. 526 p.

US DEPARTMENT OF AGRICULTURE (USDA), US DE-

PARTMENT OF THE INTERIOR (USDI). 1994. Record of decision for amendments to Forest Service and

89(3)

Bureau of Land Management planning documents within the range of the Northern Spotted Owl, and standards and guidelines for management of habitat for late-successional and old- growth forest related species within the range of the Northern Spotted Owl. Portland, OR: USDA Forest Service and USDI Bureau of Land Man- agement.

US FISH AND WILDLIFE SERVICE (USFWS). 1990. En-

dangered and threatened wildlife and plants; de- termination of threatened status for the Northern Spotted Owl. Federal Register 55:26114-26194.

WARD JP. 1990. Spotted Owl reproduction, diet and prey abundance in northwest California [thesis]. Arcata, CA: Humboldt State University. 70 p.

YoM-Tov Y, WOOL D. 1997. Do the contents of Barn Owl pellets accurately represent the proportion of prey species in the field? Condor 99:972-976.

US Fish and Wildlife Service, Western Washington Fish and Wildlife Office, 510 Desmond Drive SE, Lac-

ey, Washington 98503, [email protected] (KBL); Nova Scotia Department of Natural Resources, 136 Exhibition Street, Kentville, Nova Scotia B4N 4E5 (MFE); Department of Biology, Laurentian Universi-

ty, Sudbury, Ontario P3E 2C6 (PAC); British Colum- bia Ministry of Environment, 2975 Jutland Road, Vic-

toria, British Columbia V8W 9M1 (JH); 16445 Point Lena Loop Road, Juneau, Alaska 99801 (JPH). Sub-

mitted 07 February 2008, accepted 16 April 2008. Corresponding Editor: Joan Hagar.

NORTHWESTERN NATURALIST 89:190-192 WINTER 2008

AERIAL MANIPULATION OF VOLES BY COMMON RAVENS

PAUL HENDRICKS

Key words: Common Raven, Corvus corax,

voles, Microtus, behavior, predation, play, Mon- tana

Common Ravens (Corvus corax) perform a

number of unusual behaviors, such as rolling

and sliding in snow, hanging from branches by

their bills or feet, and manipulating a variety of inanimate objects in their bills or feet while on the ground or in flight (Bent 1946; Heinrich 1989, 1999; Ratcliffe 1997; Brazil 2002). In many

contexts the activities appear to be play behavior (Ficken 1977; Heinrich and Smolker 1998), sometimes seemingly without purpose, but at other times potentially related to adult behaviors involved in courtship or the acquisition of food. Two observations of food manipulation by airborne ravens that I describe below match descriptions of raven play with inanimate objects (Heinrich and Smolker 1998).

At 10:30 MST on 8 January 2006, while tra- versing grassy slopes on Mt. Sentinal above the



barred owls eating worms and slugs: the advantage in not being picky eaters

Documents