Section: Ecology
Topic: Ecology, Population biology

Delayed dichromatism in waterfowl as a convenient tool for assessing vital rates

Tableau, Adrien1  ; Henderson, Iain2; Reeber, Sébastien3; Guillemain, Matthieu1 ; Maillard, Jean-François1; Caizergues, Alain1 
1 French Biodiversity Agency (OFB), France
2 Animal and Plant Health Agency, United Kingdom
3 Société Nationale pour la Protection de la Nature, France

Corresponding author(s): Tableau, Adrien (adrien.tableau@ofb.gouv.fr)

10.24072/pcjournal.531 - Peer Community Journal, Volume 5 (2025), article no. e32.

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Monitoring the number of individuals is by far the most popular strategy for studying the environmental factors that determine population dynamics and for measuring the effectiveness of management actions aimed at population recovery, control or eradication. Unfortunately, population size monitoring is inefficient in identifying the mechanisms underlying demographic processes and, in particular, in assessing the extent to which population growth rate is influenced by changes in adult survival rather than variations in reproductive parameters. In many waterfowl species, sexual dichromatism is observed in adults, while immatures of both sexes display a plumage pattern similar to that of adult females. In these species, the apparent proportion of males increases as the female-like immature males gradually take on the plumage of adult males. The difference between the apparent sex ratio before and after the young reach sexual maturity then provides information about the age ratio of a population. Using winter counts that distinguished between female-like and male-like individuals of two non-native populations of Ruddy duck Oxyura jamaicensis, a species that exhibits such a plumage pattern, we present a non-invasive method based on the apparent sex ratio to split population growth rate into adult survival and recruitment rates (the latter also referred to as productivity). This method can correctly detect annual changes in vital rates, supporting the assumption that counts conducted in an appropriate time window reflect the age structure of a population. We exemplify how the respective contributions of survival and productivity to the population growth rate are essential for understanding the processes behind demographic dynamics. Finally, we point out some best practices to correctly apply the ``apparent sex ratio'' method described here. 

Published online:
DOI: 10.24072/pcjournal.531
Type: Research article
Keywords: alien species, demography, fecundity, harvest, intrinsic growth rate, reproductive success

Tableau, Adrien 1; Henderson, Iain 2; Reeber, Sébastien 3; Guillemain, Matthieu 1; Maillard, Jean-François 1; Caizergues, Alain 1

1 French Biodiversity Agency (OFB), France
2 Animal and Plant Health Agency, United Kingdom
3 Société Nationale pour la Protection de la Nature, France
License: CC-BY 4.0
Copyrights: The authors retain unrestricted copyrights and publishing rights 
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Tableau, Adrien; Henderson, Iain; Reeber, Sébastien; Guillemain, Matthieu; Maillard, Jean-François; Caizergues, Alain. Delayed dichromatism in waterfowl as a convenient tool for assessing vital rates. Peer Community Journal, Volume 5 (2025), article  no. e32. doi : 10.24072/pcjournal.531. https://peercommunityjournal.org/articles/10.24072/pcjournal.531/

PCI peer reviews and recommendation, and links to data, scripts, code and supplementary information: 10.24072/pci.ecology.100706

Conflict of interest of the recommender and peer reviewers:
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article.

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