SEX AND AGE-SPECIFIC ANNUAL SURVIVAL IN A NEOTROPICAL MIGRATORY SONGBIRD, THE PURPLE MARTIN (PROGNE SUBIS)

We estimated apparent annual survival probability of adult Purple Martins (Progne subis) using a 14-year data set from a population in northwestern Pennsylvania. We modeled age, sex, and year effects on adult survival using known-age birds (585 males and 392 females) first banded or resighted as one-year-olds in two core breeding colonies. We resighted banded birds at (1) the two core breeding colonies, (2) other breeding colonies within 50 km of the core colonies, and (3) a large premigratory roost that attracts adult Purple Martins from colonies <= 200 km away. Apparent annual Survival probability for one-year-olds increased by 0.08 when we included encounters outside the core colonies. Survival probability for older males and females was largely unaffected, a result of their high breeding-site fidelity. The model with age-specific survival (1 year old, 2-4 years old, >= 5 years old) and an age*sex interaction had the strongest support when all encounters were included. Apparent annual survival of one-year-old females (0.48 +/- 0.03 [SE]) was lower than that of one-year-old males (0.59 +/- 0.02), but we detected no sex differences in survival among older birds (2-4 years old: females, 0.64 +/- 0.02; males, 0.62 +/- 0.02). We found evidence of senescence, because birds at least five years old had lower apparent survival (females: 0.51 +/- 0.06; males: 0.52 +/- 0.05). Fully time-dependent models had low support, including those evaluating the relationship between annual variation in prevalence of West Nile virus and the El Nino Southern Oscillation Index, a key climate variable. Received 29 February 2008, accepted 28 October 2008.