were more common in the diet in spring-summer than in
autumn-winter. Small mammals were also more frequent in the
diet of owls in 2002 than in the other years of the study.
Although population dynamics of small mammals in dry forests
of central Argentina and particularly those of sigmodontinae
rodents (e.g. Calomys sp., Graomys griseoflavus and Akodon molinae)
are not well defined, it is known that abundances of these
rodent species fluctuate seasonally. Several studies, for example,
have found peaks in field abundance of small mammals in
autumn and spring with noticeable and marked declines during
winter (Biseglia et al., 2011; Corbalan and Ojeda, 2004; Sarasola
et al., 2007). Some of these studies also found differences in
small mammal abundances between years, probably due to food
availability/constraints, climate factors, or both (Corbal
an and
Ojeda, 2004). Birds were more frequent in the owl's diet in
spring-summer than in autumn-winter. Density of birds in the
calden forest, and particularly those for the bird species found in
the diet of owls except one (Sturnella loica), are also higher in
warmer than in colder seasons (Sosa, 2008), suggesting that the
owl's predation on birds is constrained by seasonal fluctuations.
Thus, variation in the abundance of small mammals and birds in
the diet of ferruginous pygmy-owls seems to reflect, at least in
part, field availability and abundance. There is no available information
on the effects of vegetal structure and habitat type on
field abundance of these prey groups.