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Identifier

000440979

Title

Temporal variation in the sex ratio of a colonial raptor : the case of Eleonora’s falcon (Falco eleonorae)

Alternative Title

Χρονική διακύμανση της αναλογίας φύλου σε ένα αποικιακό αρπακτικό είδος πτηνού: η περίπτωση του Μαυροπετρίτη (Falco eleonorae)

Author

Μποτσίδου, Πετρούλα Κ.

Thesis advisor

Πουλακάκης, Νικόλαος

Reviewer

Ξηρουχάκης, Σταύρος
Κωτούλας, Γεώργιος

Abstract

Eleonora’s falcon (Falco eleonorae) is a long-distance migratory bird of prey, which winters in Madagascar and breeds in the Mediterranean Sea, with Greece holding up to 90% of the global population. The species breeds later than any other bird species globally, having synchronized its breeding period with the migration of the small passerine birds, upon which it feeds and raises its young. Clutch size ranges between 1 to 3 eggs with female chicks being generally larger than males, and tend to be more dispersive. Even though there are several studies regarding the biology and behaviour of the species, little is known about their sex ratios. Studying sex ratios of wild animals not only aids the monitoring of reproductive health and growth rates of their populations, but also provides valuable information regarding the evolution of the species. In natural populations, offspring sex ratios can greatly vary from parity (1:1 sex ratio) and the observed biases are generally considered to be speciesspecific adaptive strategies that are shaped by natural selection. In birds, offspring sex ratio biases are correlated with specific factors, such as season and order of hatching, food abundance, parental quality or social environment. In the only study on the sex ratios in Eleonora’s falcon, a temporal variation in the offspring sex ratio was observed, with females outnumbering males early in the breeding season. The aim of this study was to assess the sex ratio of Eleonora’s falcon offspring by using molecular sexing techniques and to associate any observed variations in the proportion of sexes with specific ecological and biological factors. Additionally, the sexual size dimorphism of offspring was investigated. The results showed a slightly male-biased overall sex ratio (Sex ratio = 0.51) that varied temporally, being female-biased early in the breeding season, as well as early within a brood. The sex ratio also varied with nest orientation and brood size, but did not differ with nest type. Female chicks were shown to be 11% heavier than males, and females were larger than males independently of rank, season, or brood size. The consistency in the results across years, together with the unequal costs of daughters and sons suggests an adaptive sex ratio bias scheme that is being regulated by different sex allocation strategies depending on the parental quality, the abundance of food and the quality of the habitat. However, continued detailed research is necessary to safely interpret the adaptive significance of the observed bias in sex ratio, and to reject the likelihood of artefacts.

Language

English

Subject

Aegean Sea

Evolutionary adaptation

Fledglings

GLMMs

Migratory bird

Molecular sexing

Αιγαίο Πέλαγος

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