Sex-specific recruitment rates contribute to male-biased sex ratio in Adélie penguins

Virginia Morandini, Katie M. Dugger, Annie E. Schmidt, Arvind Varsani, Amélie Lescroël, Grant Ballard, Phil O.B. Lyver, Kerry Barton, David G. Ainley

Research output: Contribution to journalArticlepeer-review

Abstract

Sex-related differences in vital rates that drive population change reflect the basic life history of a species. However, for visually monomorphic bird species, determining the effect of sex on demographics can be a challenge. In this study, we investigated the effect of sex on apparent survival, recruitment, and breeding propensity in the Adélie penguin (Pygoscelis adeliae), a monochromatic, slightly size dimorphic species with known age, known sex, and known breeding history data collected during 1996–2019 (n = 2127 birds) from three breeding colonies on Ross Island, Antarctica. Using a multistate capture–mark–recapture maximum-likelihood model, we estimated apparent survival ((Formula presented.)), recapture (resighting) probability ((Formula presented.)), and the probability of transitioning among breeding states and moving between colonies ((Formula presented.); colony-specific non-juvenile pre-breeders, breeders, and non-breeders). Survival rate varied by breeding status and colony, but not sex, and pre-breeders had higher survival rates than breeders and non-breeders. Females had a higher probability of recruiting into the breeding population each year and may enter the breeding pool at younger ages. In contrast, both sexes had the same probability of breeding from year to year once they had recruited. Although we detected no direct sex effects on survival, the variation in recruitment probability and age-at-first reproduction, along with lower survival rates of breeders compared to pre-breeders, likely leads to shorter lifespans for females. This is supported by our findings of a male-biased mean adult sex ratio (ASR) of 1.4 males for every female ((Formula presented.) proportion of males = 0.57, SD = 0.07) across all colonies and years in this metapopulation. Our study illustrates how important it can be to disentangle sex-related variation in population vital rates, particularly for species with complex life histories and demographic dynamics.

Original languageEnglish (US)
Article numbere10859
JournalEcology and Evolution
Volume14
Issue number2
DOIs
StatePublished - Feb 2024

Keywords

  • Adélie penguin
  • adult sex ratio (ASR)
  • demographics
  • recruitment
  • seabird
  • sex-specific
  • survival

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Ecology
  • Nature and Landscape Conservation

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