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7 March 2018 Age effects on survival of Amazon forest birds and the latitudinal gradient in bird survival
Alejandra Pizarro Muñoz, Marc Kéry, Pedro Vitor Martins, Gonçalo Ferraz
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Abstract

The search for explanations of the well-documented positive relationship between latitude and avian clutch size has created the expectation that tropical birds should balance their smaller clutch sizes with relatively high survival probabilities. So far, efforts to detect a latitudinal gradient in survival have found no statistical support, leading to the hypothesis that a gradient may be present in the survival of juveniles alone. Such a gradient could be masked by the data on adults when field records make no distinction between ages. We aimed to (1) assess the effect of age on survival of tropical birds by estimating age-specific annual apparent survival probabilities for a set of 40 passerine understory species from the central Brazilian Amazon and (2) test the hypothesis of a latitudinal gradient in adult survival with a meta-analysis of tropical and temperate-zone forest passerine survival probabilities at study areas from Peru to Alaska. We estimated age-specific survival using a hierarchical, multispecies Cormack-Jolly-Seber (CJS) model that treats species-specific parameters as random effects. To extend our analysis to data on birds of unknown age at the time of banding, we developed a novel CJS model with a mixture component for the survival of birds of unknown age. We found a strong effect of age on survival at our site, with juveniles having lower survival than adults. The meta-analysis of 342 survival estimates from 175 species and a latitude span of >60 degrees revealed a negative effect of latitude on survival, which supports the widely accepted hypothesis that, on average, tropical birds have higher annual survival than their temperate counterparts. We conclude that there is no need for an alternative latitudinal trend in juvenile survival to account for the general trend in clutch size.

© 2018 American Ornithological Society.
Alejandra Pizarro Muñoz, Marc Kéry, Pedro Vitor Martins, and Gonçalo Ferraz "Age effects on survival of Amazon forest birds and the latitudinal gradient in bird survival," The Auk 135(2), 299-313, (7 March 2018). https://doi.org/10.1642/AUK-17-91.1
Received: 19 May 2017; Accepted: 27 December 2017; Published: 7 March 2018
KEYWORDS
age uncertainty
age-mixture survival model
age-specific survival
AMAZON
Cormack-Jolly-Seber
Hierarchical model
tropical birds
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