Meeting Abstract
Among the hypotheses explaining nest-site selection and survival, the ‘total-foliage’ hypothesis predicts that nests concealed in vegetation should have higher survival. An alternative, the ‘predator proximity’ hypothesis, states that nests placed further away from predators will have higher survival. We examined these hypotheses on Navarino Island, where the predator assemblage has recently changed with the introduction of ground predators. During three breeding seasons, we monitored nests for the five most abundant open-cup forest-dwelling passerines. We identified nest predators using camera traps and assessed habitat characteristics that may affect nest-site selection and survival. The main nest predator was the native raptor Milvago chimango, whereas Neovison vison was the only ground predator, depredating one nest. Birds selected nest-sites with more understory cover, which, according to the total-foliage hypothesis, would provide more concealment against predators. However, understory cover did not influence nest survival. Some of the habitat characteristics that influenced nest survival of these species were consistent with the total-foliage hypothesis (e.g., nest concealment), whereas others supported the predator proximity hypothesis (e.g., nest height from the ground). There seems to be a disconnect between birds assessing the risk of predation (and selecting the appropriate nest-site) and the actual risk of predation. This could be due to recent changes in the predator assemblage caused by the introduction of ground predators to this island. The higher survival of nests placed further off the ground suggests that ground predators may be more prevalent than what we reported based on our camera trap data.
