USING AGE RATIOS TO INFER SURVIVAL AND DESPOTIC BREEDING DISPERSAL IN HYBRIDIZING WARBLERS

Abstract

I use age ratios of males (1) to examine latitudinal and longitudinal variation in survival in Hermit and Townsend's Warblers, both Neotropical migrants, (2) to show that the estimates for male survival are significantly lower for Townsend's Warblers than for Hermit Warblers, and (3) to show that despotic territorial behavior forces yearling males into high-elevation habitats for their first potential breeding season. When breeding dispersal is high, as is the case in these warblers, recapture methods will always underestimate survival because permanent emigration cannot be distinguished from mortality, even after accounting for detection probabilities of less than 1. Reliable survival estimates are important to life history analyses and conservation planning; thus, range-wide measures of the proportion of adults may be the best approach to estimating survival for birds with high breeding dispersal. Similarly, landscape-level consequences of despotic territorial behavior have been difficult to explore except by examining age ratios across geography.