Demography of the Neotropical austral migrant Elaenia albiceps chilensis (Tyrannidae) on its breeding grounds: climate and food offer effects

Paula Marcela Presti,Susana Patricia Bravo,Víctor Rodolfo Cueto,Guillermo César Amico

doi:10.1007/bf03544438

Abstract

The White-crested Elaenia (Elaenia albiceps chilensis) is a Neotropical austral migrant that breeds in Patagonian forests and overwinter in South America tropics. We investigated White-crested Elaenia demography and the environmental conditions the specie is subjected at the northwest of Patagonia as a first attempt to elucidate its population dynamic. We studied the species abundance, individuals’ body condition, survival, productivity of young and site fidelity according to changes in rainfall patterns and food supply, during three breeding seasons (2009 to 2012). We color banded 361 adult and juvenile White-crested Elaenias. During the first studied season, precipitations were remarkably above the mean and ripe fruit supply was lower than in the other seasons, whereas the abundance of arthropods remained similar along the study. The species abundance decreased 50% across the study, while adult apparent survival rate, the number of breeding females, young productivity and site fidelity were 50% lower in the first season in comparison to the following seasons. Females presented lower body condition at arrival in the first two studied periods. Site fidelity diminished after unfavorable breeding season (i.e. low young productivity and fruit supply), especially for males, although they were more faithful than females and had a slightly higher apparent survival rate. Our results suggest that White-crested Elaenia demography is affected by changes in its main food resource supply (fleshy fruits) during the breeding season, indicating that this part of the annual cycle could be fundamental for its population dynamic.

Highlights

The study of demography and the factors that regulate populations are among the most important approaches to understand population trends
Differences in life history between North and South Hemisphere birds suggest that Southern hemisphere species have lower reproductive success that is compensated with higher adult survival
Previous studies have emphasized the importance for species with low reproductive success to compensate this demographic feature with higher adult and juvenile survival (Martin 1996, Stahl & Oli 2006)

Summary

Introduction

The study of demography and the factors that regulate populations are among the most important approaches to understand population trends. Birds demographic (abundance, survival and reproductive success) and behavioral features (site fidelity, space use and dispersal) are regulated by both intrinsic and extrinsic factors (e.g. physical and nutritional traits of individuals and food or weather variations, respectively; Martin 1996, Newton 1998). These factors interact with each other in positive and negative ways, and their implications in a population are expected to vary according to the species life history (Newton 1998). This trend has been mainly suggested for resident species, it applies to species that perform regional or long distance migrations (Martin 1996, Russell et al 2004, Blake & Loiselle 2013)

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