Brood sex ratio variation in a colonial raptor, the Eleonora's falcon, Falco eleonorae

Xirouchakis, Stavros; Botsidou, P.; Baxevani, K.; Andreou, G.; Tsaparis, Dimitris

doi:10.1016/j.anbehav.2022.11.001

Cited by 2 publications

(1 citation statement)

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“…Although this does not apparently favor a particular sex (Slagsvold et al, 1986 ), nestling sex has been found to vary according to the hatching order. In mixed‐sex broods, first‐hatched nestlings are usually females in some species, such as the Peregrine Falcon Falco peregrinus (Olsen & Cockburn, 1991 ), Montagu's Harrier Circus pygargus (Leroux & Bretagnolle, 1996 ), Eurasian Kestrel Falco tinnunculus (Blanco et al, 2003 ), Eleonora's Falcon Falco eleonorae (Xirouchakis et al, 2022 ), and Bald Eagle Haliaeetus leucocephalus (Bortolotti, 1986 ), and more often males in others such as the Harris' Hawk Parabuteo unicinctus (Bednarz & Hayden, 1991 ) and Scops Owl Otus scops (Blanco et al, 2002 ). These variations in first‐hatched nestlings are mainly due to parental control of the sex within the egg sequence and/or by food monopolization and siblicide by the first‐hatched nestling over the youngest (Bortolotti, 1986 ; Simmons, 1988 ).…”

Section: Introductionmentioning

confidence: 99%

Insularity determines nestling sex ratio variation in Egyptian vulture populations

Gómez‐López

Sanz‐Aguilar

Carrete

et al. 2023

Ecology and Evolution

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Variation in offspring sex ratio, particularly in birds, has been frequently studied over the last century, although seldom using long‐term monitoring data. In raptors, the cost of raising males and females is not equal, and several variables have been found to have significant effects on sex ratio, including food availability, parental age, and hatching order. Sex ratio differences between island populations and their mainland counterparts have been poorly documented, despite broad scientific literature on the island syndrome reporting substantial differences in population demography and ecology. Here, we assessed individual and environmental factors potentially affecting the secondary sex ratio of the long‐lived Egyptian vulture Neophron percnopterus. We used data collected from Spanish mainland and island populations over a ca. 30‐year period (1995–2021) to assess the effects of insularity, parental age, breeding phenology, brood size, hatching order, type of breeding unit (pairs vs. trios), and spatial and temporal variability on offspring sex ratio. No sex bias was found at the population level, but two opposite trends were observed between mainland and island populations consistent with the island syndrome. Offspring sex ratio was nonsignificantly female‐biased in mainland Spain (0.47, n = 1112) but significantly male‐biased in the Canary Islands (0.55, n = 499), where a male‐biased mortality among immatures could be compensating for offspring biases and maintaining a paired adult sex ratio. Temporal and spatial variation in food availability might also have some influence on sex ratio, although the difficulties in quantifying them preclude us from determining the magnitude of such influence. This study shows that insularity influences the offspring sex ratio of the Egyptian vulture through several processes that can affect island and mainland populations differentially. Our research contributes to improving our understanding of sex allocation theory by investigating whether sex ratio deviations from parity are possible as a response to changing environments comprised by multiple and complexly interrelated factors.

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