The Wilson Journal of Ornithology 124 ( 3 ): 589 - 596 , 2012 
VARIATION IN THE DIET OF WESTERN BARN OWLS (TYTO ALBA ) 
ALONG AN URBAN-RURAL GRADIENT 
PABLO TETA, 13 CARINA HERCOLINI, 2 AND GERARDO CUETO- 
ABSTRACT.—We studied geographic variation in the diet of Western Barn Owls (Tyto alba ) along a urban-rural 
gradient in central-eastern Argentina and identified 5.231 prey items. Mammals were present in all samples, whereas birds 
and amphibians were present in 79.1 and 50.09r of the samples, respectively. There were significant ditterences in 
vertebrate assemblages consumed by Barn Owls at the opposite extremes ol the gradient. Native sigmodontine rodents 
comprised 85.8^ of the total prey items, especially towards periurban and rural areas. Exotic murid rodents were the main 
prey item in urban sites, while birds increased in frequency in urban and periurban areas. Food niche breadth and 
standardized food niche breadth values were higher at intermediate levels of urbanization (= periurban). This periurban 
peak' in species diversity is a relativ ely well-known pattern, previously reported for taxa such as birds, lizards, bumblebees, 
and butterflies among others. The trophic habits of Barn Owls along this gradient were mostly similar to those reported in 
other studies in southern South America, where the main prey items were native rodents and tood niche breadth values 
'measured at the level of Orders) were low. Western Bam Owls in our study maintained specialization as a micromammal 
predator. Received 13 October 2011. Accepted lb April 2012. 
The Western Barn Owl (Tyto alba ) is one of the 
most common and best-studied raptors in Ihe 
world (Marks et al. 1999). Its food habits have 
been widely documented throughout its distubu- 
lional range, demonstrating this species has a 
marked preference for mieromammalian prey 
(Taylor 2004). Despite the abundant information 
about its food habits in southern South America 
(e.g., Bellocq 2000, Bo et al. 2007), its trophic 
ecology in temperate latitudes is strongly biased 
towards studies in agricultural or relatively 
undisturbed grassland areas (e.g., Faverin 1987, 
Bellocq 1998. Leveau et al. 2006, Gonzalcz- 
bischer et al. 2011). The diet of urban and 
periurban-dwelling Barn Owls in this same area 
ls poorly known with a few exceptions (e.g.. 
Massoia 1988, 1989). Literature about dietary 
responses at regional scales, especially along 
abrupt environmental gradients, is also scarce 
le -g-. Travaini et al. 1997, Leveau et al. 2006, 
Trejo and Lambertucei 2007). 
Bam Owls commonly breed in urban areas that 
provide suitable nest sites (e.g.. Salvati et al. 
-002), hut the trophic ecology of the species in 
Oiese habitats is poorly known. Vargas et al. 
(| 9S4) indicated birds and reptiles accounted lor 
‘Unidad de lnvestigacidn Dfvcrsidad, Sistematica y 
Evnluciiin. Centro Nacional Patagfinico. CC 128. 9120 
Puerto Madryn. Chubut. Argentina. 
Departamento de Ecologia. Genetica y Evolueion, 
Eaculiad de Ciencias Exactas y Naturalcs, Umversidad de 
Buenos Aires. Avenida Intendente Giiiraldos 216, Ciudad 
Tnivcrsitaria. Pabellfin II, 4 Piso. (C1428EHA). Buenos 
Aires. Argentina. 
’Corresponding author; e-mail: antheca@yahoo.com.ar 
>50Cr of the prey items at urban locations in 
southern Spain, suggesting that small mammals 
were secondary resources in urban habitats. Use 
of alternative prey in urban environments was also 
recorded for central Argentina, where bats were 
seasonally dominant in the diet of this ow l. Salvati 
et al. (2002) and Charter et al. (2007), in contrast, 
found high rodent consumption in urbanized 
neighborhoods of central Italy and Israel. Under¬ 
standing food preferences of this species of 
special concern in relation to other parameters 
(e.g., breeding success, habitat use) may provide 
useful information Tor a variety of habitats, 
including urban and rural areas (Salvati et al. 
2002). The objective of our study was to provide 
new information on the trophic ecology of 
Western Barn Owls along a urban to rural gradient 
in central-eastern Argentina. 
METHODS 
Study Area .—The area studied is between 34 
00 to 34 50’ S and 57 59 to 59^ 11' W, Province 
of Buenos Aires, central-eastern Argentina 
(Fig. 1), including the City of Buenos Aires and 
its influence area or l Gran Buenos Aires’. The 
area was originally covered by grasslands, patches 
of xerophylous forests, wetlands, and subtropical 
riverside forests (Cabrera 1968). This landscape 
has been gradually modified by agriculture and 
human settlement since formation of the city of 
Buenos Aires in the 16* century (Morello et al. 
2000). Today, this area is one of the most 
populated in southern South America with —13 
million people (Instituto Nacional de Estadisticas 
y Censos; http://www.indec.gov.ar/). The matrix 
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