a contribution from barn owl pellets analysis to known micromammalian distributions in buenos aires...

Mammalia 74 (2010): 97–103 � 2010 by Walter de Gruyter • Berlin • New York. DOI 10.1515/MAMM.2009.069

2010/69

Article in press - uncorrected proof

Short Note

A contribution from Barn Owl pellets analysis to known

micromammalian distributions in Buenos Aires province,

Argentina

Pablo Teta1,*, Carlos M. Gonzalez-Fischer2, MarianoCodesido2 and David N. Bilenca2

1 Museo Argentino de Ciencias Naturales ‘‘BernardinoRivadavia’’, Avenida Angel Gallardo 470, (C1405DJR)Ciudad Autonoma de Buenos Aires, Buenos Aires,Argentina, e-mail: [email protected] Departamento de Ecologıa, Genetica y Evolucion,Facultad de Ciencias Exactas y Naturales, Universidad deBuenos Aires, Avenida Intendente Guiraldes 2160, CiudadUniversitaria, Pabellon II, Cuarto piso, (C1428EGA)Ciudad Autonoma de Buenos Aires, Buenos Aires,Argentina

*Corresponding author

Keywords: agroecosystems; Pampean region; Rodentia;Sigmodontinae; Tyto alba.

The analysis of owl pellet samples is an extremely valuabletool for mammalogists (Yalden and Morris 1990). Studies onthis topic around the world are eloquent about the potentialand limitations of this methodology. For example, owl pelletscan be used for inventorying small mammal communities(Cueto et al. 2008), studying small mammal distributionthroughout geographical gradients (Avery et al. 2002, 2005,Pardinas et al. 2003, Leveau et al. 2006), delimiting distri-butions on a regional scale (Avery et al. 2002, 2005, Pardinaset al. 2003, 2004), or to track abundance changes in theirpreys, both spatially and temporally (Fulk 1976, Love et al.2000, Millan de la Pena et al. 2003). In addition, owl pelletstudies present advantages over traditional survey methods,because raptors can prey on rare species or in species noteasily detected with other methods (e.g., traps; Yalden andMorris 1990).

It is usually accepted that micromammalian distributionsin the Pampean region of Buenos Aires province, central-eastern Argentina, are relatively well established. However,a detailed study of available information clearly demonstrat-ed that this assertion is partially incorrect (Pardinas et al.2004, in press). Much of the work done in this provinceencompasses part of the northern, eastern, and some south-eastern areas, mostly in or near the littoral fringe of La PlataRiver and the Atlantic coast (Galliari and Goin 1993). How-

ever, a very different situation is the norm for the rest of thelarge territory of the province, including some southern andmost of the central portions (Pardinas et al. 2004, in press).

In this study, we present the results of an extensive smallmammal survey conducted in the Pampean region of theBuenos Aires province through the analysis of Barn OwlwTyto alba Scopoli 1769 (Aves, Tytonidae)x pellet samples.Although these collections were part of another study, itquickly became apparent that they were adding to the knowndistribution pattern of some micromammals. In addition, weprovided some comments regarding species abundance atdifferent localities and the biogeographic implications ofsome of these records.

The province of Buenos Aires (307,571 km2) is located incentral-eastern Argentina, between 338–418 S and 578–638

W. Its territory is almost entirely included within the Pam-pean eco-region and encompasses four ecological units ordistricts that can be distinguished according to differences ingeomorphology, soils, drainage, physiography, land use pat-terns, and vegetation: the Rolling Pampa, the Southern Pam-pa, the Flooding Pampa and the Inland Pampa (Soriano etal. 1992). Native grasslands through most of the Pampeanregion were gradually converted to agroecosystems over thepast two centuries. Primary uses of the land, with some dif-ferences between areas, are for agriculture and livestockbreeding (see Baldi and Paruelo 2008). Climate of the Pam-pean region is characterized by an east-west moisture gra-dient and increasing continentality toward the northwest(Burgos 1968). Mean annual precipitation decreases from1200 mm in the northeastern to 600 mm in the southwesternregions. Mean annual temperatures show a similar trend,with values between 238C (north) and 208C (south) for Jan-uary and 108C (north) and 78C (south) for June (Burgos1968).

Fresh Barn Owl pellets were collected during July andAugust 2006–2007 (winter) and January and February2007–2008 (summer) from nest sites distributed in the fourdistricts of the Pampean region included in the Buenos Airesprovince (Figure 1). One to three deposit places were foundat each locality. The diet of Tyto alba at the localities ofDiego Gaynor and Villa Cacique were previously studied byBellocq (1990) and Leveau et al. (2004), respectively. Allother localities are studied for the first time. Mammalianpreys were identified to the lowest taxonomical level possi-ble by the examination of the skull and dentaries, followingpublished literature (Massoia and Fornes 1965, 1969, Mas-

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98 P. Teta et al.: Owl pellets and micromammalian distributions


Figure 1 (A) Studied localities and (B–F) new locality records (black circles) for selected micromammal species in Buenos Aires province,central-eastern Argentina. Previous records are shown with gray circles and were compiled from several sources (Massoia 1976, Galliari etal. 1991, Pardinas 1999, Galliari and Pardinas 2000, Flores et al. 2007).

soia 1976, Galliari and Pardinas 2000) and by comparisonswith reference collections housed at the Museo de CienciasNaturales ‘‘Bernardino Rivadavia’’ (Buenos Aires, Argentina).Studied samples are housed in the Laboratorio de Ecologıade Poblaciones, Universidad de Buenos Aires (Argentina).The taxonomy employed here follows Wilson and Reeder(2005), with modifications according to D’Elıa et al. (2008a).

We analyzed a total of 90 samples from 62 localities iden-tifying a total of 32,892 prey-items. At least 14 taxa arerepresented in the studied samples (Table 1). In two cases,including the native rodent genus Calomys Waterhouse 1837and the exotic Rattus Fischer 1803, it was not determinedwhether one or two species are involved. Two species ofCalomys – C. laucha (Fischer 1814) and C. musculinus(Thomas 1913) – are widely sympatric in the Pampeanregion of the Buenos Aires province (Massoia and Fornes1965), accounting for up to 60% of the small mammal com-munities in most of our studied localities. All micromammalspecies found in the owl pellet samples belonged to speciespreviously cited for the Pampean region (Galliari et al. 1991,Pardinas et al. in press). The most relevant findings arediscussed in the following paragraphs.

Previous records for the small marsupial Monodelphisdimidiata (Wagner 1847) (Figure 2A) correspond to four iso-lated areas in the north, northeastern, southeastern, andsouthwestern corners of the province (Flores et al. 2007).Our finding partially fills the gap between the southern pop-ulations, enlarging its distribution ca. 90 km to the west andnorth from the previous nearest records in this area. In addi-tion, we found this species in the Flooding Pampa, an areawithout previous references for this species.

New locality records for the marsh rat Holochilus brasi-liensis (Desmarest 1819) (Figure 2B) enlarge its distributionca. 100 km to the west in the northwestern corner of theBuenos Aires province. In addition, its presence is confirmedin the Flooding and Inland pampas, two areas where theprevious records were mostly peripheral (Massoia 1976).

Necromys lasiurus (Lund 1840) (Figure 2C) has a wideand fragmentary distribution in the Pampean region (Galliariand Pardinas 2000). Our findings in the northern corner ofBuenos Aires province expanded ca. 50 km to the west itsknown distribution and almost triplicate its range area in thissector. A similar situation was observed with Necromys obs-curus (Waterhouse 1837) (Figure 2D). This species enlarged



P. Teta et al.: Owl pellets and micromammalian distributions 99


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Figure 2 Specimens recovered in the owl pellets from the Pam-pean region of the Buenos Aires province, Argentina: (A) Mono-delphis dimidiata w59x, lateral view of the right maxillary; (B)Holochilus brasiliensis w59x, ventral view of the skull; (C) Necromyslasiurus w5x, ventral view of the skull; (D) Necromys obscurus w59x,ventral view of the skull; (E) Oxymycterus rufus w51x, ventral viewof the skull; (F) Reithrodon auritus w53x, ventral view of the skull.The number between brackets corresponds to the locality of collec-tion (see Table 1). Scales5 mm.

its distribution to the interior grasslands of the Buenos Airesprovince ca. 110 km to the northwest from its previous near-est record. In addition, its small distributional range is almostduplicated in Argentina, restricted to the date to humid grass-lands in coastal areas and hilly environments (Galliari andPardinas 2000). It is important to note that owing to itsrestricted and fragmented distribution, this species was listedas Near Threatened by the IUCN (D’Elıa et al. 2008b).

Despite that our records for Oxymycterus rufus (Fischer1814) (Figure 2E) are almost included within the recentrange of this species, the reference for Diego Gaynor is note-worthy. The small mammal community of this locality was

largely studied in the past three decades and no previousrecords for this species were made until recent years (Bellocq1990). In fact, O. rufus was registered for the first time inthis area around the decade of 2000 when some individualswere trapped in borders of cultivate fields (Bilenca et al.2007). Our record is the second for this locality, which islocated 40 km to the south of the nearest previous reference.

Reithrodon auritus (Fischer 1814) (Figure 2F) is mostlyrestricted to the eastern and southern half of the province.New locality records, showing relatively high frequencies(7–33% of the total identified specimens) in some sites, fillthe gap between previous records in the Flooding and South-ern Pampas. This is an interesting finding because R. auritusis in general a non-abundant element in the Pampean region(see Prado et al. 1987).

The sigmodontine rodent communities of the Pampeanregion are characterized by the dominance of Calomys spp.,Akodon azarae (Fischer 1819), and Oligoryzomys flavescens(Waterhouse 1837) (Pardinas et al. in press). Ecological,genetic, and paleontological studies have associated the prev-alence of these species, and in particular of Calomys spp.,with the transformation of large surfaces from natural pas-tures and grasslands to crop fields (Pardinas 1995, 1999,Gonzalez-Ittig et al. 2007, Pardinas et al. in press). This sit-uation created favorable conditions for Calomys spp., allow-ing populations to increase in size and to expand (Bilencaand Kravetz 1995, Pardinas 1995). These same conditionswere perhaps responsible for the fragmentation of the distri-butional ranges of some species, including local (e.g., Necro-mys lasiurus in some coastal areas; see Galliari and Pardinas2000) or total extinctions, and the decrease in the abundanceof others (e.g., Reithrodon auritus; Pardinas 1999). Our sur-vey, encompassing a surface of ca. 150,000 km2 of mostlyunstudied areas, confirms this assertion. In fact, despite thatwe found a significant extension of range distributions forsome species, the main distributional patterns do not changesignificantly (e.g., Necromys lasiurus is still restricted to fourmain discontinuous populations).

Our data confirm the importance of Tyto alba in recordingsmall mammals and show that the analysis of regurgitatedpellets can be an important tool for the inventory of rare ordifficult-to-trap small mammals. This methodology permitsto sample small mammal communities through very largeareas at low cost, allowing detection of isolated populationsof species with fragmentary distributions. Moreover, samplesthrough different years are useful to detect small mammalchanges in the communities, such as range expansions orextinctions, both at local and regional levels. In addition,taking into account the recent changes observed in the Pam-pean biota with regard to different land use and landscapestructure (Attademo et al. 2005, Schrag et al. 2009), owlpellet analysis can be a valuable tool in evaluating the evo-lution of small mammal composition in short-term periods(Love at al. 2000).

Acknowledgements

We would like to thank Lucas and Carlos Leveau, Laura Solari andJennifer Tregoning for their assistance during fieldwork. Ulyses F.J.





Pardinas and an anonymous reviewer made valuable comments ona first draft of this work. This study was funded by the ConsejoNacional de Investigaciones Cientıficas y Tecnicas (CONICET,Argentina), the Universidad de Buenos Aires (grants UBACyTX282 and X406), and the Instituto Nacional de Tecnologıa Agro-pecuaria (INTA, Argentina; PNECO 1302).

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a contribution from barn owl pellets analysis to known micromammalian distributions in buenos aires...

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