Effects of intrinsic and time-specific factors on daily nest survival of birds in a semiarid area of South America (Caatinga)

Nest predation is a determinant of reproductive success of tropical birds and its effects can vary in space, time and due to intrinsic factors of the species. In this study, we conducted a preliminary investigation on changes in the risk of nest predation on Caatinga birds due to intrinsic factors (nest type and taxonomic group) and time-specific factors (breeding season and nest abundance). We located and monitored bird nests during the breeding seasons of 2012 (n = 33 nests) and 2013 (n = 45) in a mixed landscape of anthropogenic and natural sites. We use the MARK program that uses known-fate models to calculate Daily Nest Survival Estimates (DNS) and evaluate the effect of covariates on DNS estimates. Predation was the main cause of nest loss (n = 54). In the analysis of intrinsic factors, the best model included the type of nest to explain variation in estimates. DNS declined across the breeding season for all nest types, but estimates of closed nests (between 0.996 and 0.851) were higher than those of open nests (between 0.985 and 0.629). For time-specific factors, the best models for each breeding season included the quadratic effect of nest abundance to explain the variation in DNS. There was an inverse relationship between the abundance of nests and nest predation. The high importance of predation and the effect of the type of nest showed that the reproductive success of the birds studied is due to similar factors to those found in other Neotropical environments. On the other hand, locally-specific effects, such as low reproductive success and inverse relationship between abundance and nest predation risk, demonstrate the need for further exploration of this theme within the Caatinga avifauna.