Birds Project

Research done

Since some years ago, and more intensively since 1993, we have been studying the granivorous birds–seeds system in the Reserve of Ñacuñán, in the central Monte desert, Argentina. We have focused our research on the trophic as well as the reproductive ecology of these organisms.

During the course of our studies on birds' feeding behaviour and diet, we have found that six species of the Emberizidae family are the main seed consumers in Ñacuñán (Lopez de Casenave 2001, Marone et al. MS), and that they feed mainly upon grass seeds (83% of the seeds found in the digestive tracts belong to this family, Marone et al. MS). From a bioenergetic perspective, the relationship between the abundance of seeds and granivorous birds during winter suggests that birds would only occasionally suffer from a food limitation (Lopez de Casenave 2001). We have also studied such relationship spatially. At the habitat scale, birds do not seem to be selecting habitats in response to seed abundance during winter (Marone et al. 1997), whereas at the landscape scale this would be an important variable for the determination of the space use patterns in some granivorous birds (Marone 1991). These results suggest that seed abundance during winter would not be a liming factor for the spatio-temporal dynamics of granivorous birds (nevertheless, this variable does not necessarily reflect the seed amount which is actually available for birds, see Feeding preferences and Use of space). During the reproductive season (spring-summer) the abundance of granivorous birds is significantly lower in dry years, and this would be associated with a decrease in the seed offer (Marone 1995). This reduction in the abundance of granivorous birds is due to the fact that some species leave or do not visit the study area during those periods.

Taking the birds' seed consumption effects into account, we have found that seed banks suffer a considerable loss of grass seeds during autumn-winter (around 50%), mainly of recently produced seeds (Marone et al. 1998). Thus, granivorous birds would have a qualitative and quantitative impact on seed reserves in the central Monte desert.

As regards reproductive ecology of granivorous birds, we have seen that they suffer a high nesting predation pressure in the Reserve as well as in the nearby ranches (usually >90% on average, Mezquida & Marone 2001). Hence, nest predation could constitute an important selective force at an ecological and an evolutionary level. It all seems to indicate that the selection of nesting sites does not result in a decrease in predation (Mezquida & Marone 2002).