“Sex-specific heterogeneity in fixed morphological traits influences individual fitness in a monogamous bird population”

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Floriane Plard, Susanne Schindler, Raphaël Arlettaz, and Michael Schaub

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Population dynamics of a monogamous bird is driven by sex-specific life-history strategies

An adult hoopoe with its particular long bill and feathered crest.
(Credit: Raphaël Arlettaz)

Individuals differ in sex and intrinsic quality and their body condition changes over the course of the year—all of which results in individual differences in survival and reproductive abilities. Despite this fact, we lack empirical knowledge about how individual heterogeneity influences individual demographic performance and how it affects population dynamics, because models of population dynamics typically focus on average demographic rates, excluding possible differences in survival and reproductive performance among individuals. In this study, researchers from the Swiss Ornithological Institute, in collaboration with researchers from the Universities of Bern and of Bristol, study the influence of individual intrinsic quality and annual condition on the dynamics of a population of hoopoes.

Hoopoes breed in nestboxes installed in vineyards and fruit-tree plantations in the Swiss Alps.
(Credit: Michael Schaub)

The hoopoe is a medium-sized monogamous bird species. The study population is located in the Swiss Alps, where hoopoes breed in nestboxes installed in vineyards and fruit-tree plantations. Results show that males and females contribute differently to population growth, with high-quality males contributing much more than females and low-quality males. High-quality males are characterized by large morphological size and high survival compared to low-quality males and females. Although females live shorter lives, they have a strong impact on annual reproductive success. Taking account of partner quality and availability, this study shows that annual reproductive success is influenced by the condition and the quality of both sexes.

A young brood of hoopoes.
(Credit: Michael Schaub)

While individual condition influences the timing of breeding, which strongly affects clutch size, female quality and to a lesser extent male quality shape the number of fledglings produced by a pair. Thus, the study provides evidence that even in a monogamous bird species with biparental care, individuals’ contribution to the population can vary between males and females and is linked to individual traits. The study also suggests that population dynamics are more strongly driven by high-quality individuals, which has consequences for the management and conservation of wild populations.