Demography of granivorous birds in the central Monte desert and its association with local food abundance

M. CECILIA SAGARIO; VICTOR R. CUETO; JAVIER LOPEZ DE CASENAVE; AGUSTÍN ZARCO

Cuzco

Congreso; IX Congreso de Ornitología Neotropical; 2011

Demographic studies are crucial to fully understand the causes of variation in the abundance of populations, which may be related to environmental conditions and resource availability. We evaluated the association of the abundance of four granivorous bird species with seed production, arthropod abundance and precipitation in the Ñacuñán Biosphere Reserve (central Monte desert, Argentina), through the analysis of productivity and survival using mark-capture-recapture techniques between 2004-2010. During the wet year of high seed production (good year), adult abundance and survival did not differ from average years, but productivity was unusually high. During the year of low seed and arthropod abundance (bad year), adult abundance and survival during the winter were extremely low, but neither abundance nor productivity differed from average years during the breeding season. Juvenile recapture rate was low and there was no association between productivity and adult abundance during the following season. Adult abundance was variable and survival was constant during average and good years, and we did not find lower adult abundance following the year of the lowest survival. We conclude that year to year fluctuations of granivore abundance do not usually come from short-term changes in survival or local productivity, but from individual movements to and from the study area instead. However, resource availability affects local abundance during exceptionally good or bad years, through increased productivity and decreased survival, respectively. Therefore, we suggest that granivorous birds? dynamics in the central Monte desert usually reflects bird movements at a regional scale, although could be locally controlled by sporadic events of limitation during bad years (crunch periods) and by opportunistic responses during exceptionally good years.