Behavioral Ecology and Sociobiology

, Volume 61, Issue 11, pp 1735–1742 | Cite as

Food supply during prelaying period modifies the sex-dependent investment in eggs of Eurasian kestrels

  • Jesús Martínez-Padilla
  • Juan A. Fargallo
Original Paper


The theory of sex allocation suggests that if the reproductive value and the cost of producing/rearing offspring differ between male and female offspring, parents should invest differently in sexes depending on environmental conditions. Female parents could allocate more resources to eggs of one sex to compensate potential sex-dependent constraints later during the nestling period. In this study, we tested the influence of environmental conditions on sexual dimorphism in eggs of Eurasian kestrels (Falco tinnunculus) by experimentally manipulating food availability before laying. We found that an increase in food abundance before laying did not increase egg mass but changed sex-dependent resource distribution in eggs. In food-supplemented pairs, but not in control pairs, egg mass and hatchling mass were similar between males and females. In addition, we found, in the food-supplemented group, that the latest hatched females showed shorter hatching times than in the control group. In control pairs, female eggs, hatchlings and nestlings were heavier than males. In addition, male fledglings in the food-supplemented group gained less mass than those in the control group. As that food abundance was only increased until the onset of laying, female kestrels were expected to invest in eggs taking food abundance before egg formation as a predictor of future conditions during brood rearing. Our study shows that environmental conditions before laying promote a subtle adjustment of the resources invested in both sexes of offspring rather than in other breeding parameters. This adjustment resulted in a shortening of hatching time of the last hatched females that possibly gives them advantages in their competitive capacity with respect to male nest-mates.


Falco tinnunculus Food supplementation Egg mass Sex investment Sexual size dimorphism 



JMP dedicates this paper to Dana, the best example of generosity, kindness and strength for living I have never ever met. We thank the Finat family for kindly allowing us to conduct the study on their property and J. San Teodoro for his collaboration in the fieldwork. El Ventorrillo field station supported this study, providing all necessary facilities during the fieldwork. J.M. Aparicio, F. Mougeot, G. Bortolotti, W. Müller, M. Marquiss and G. Blanco greatly improved an early version of the manuscript. M. Marquiss also paid special attention to the English. Two anonymous referees greatly improved an early version of this manuscript. J.A. Dávila sexed the offsprings. J. Martínez-Padilla was awarded a postdoctoral fellowship during the writing of the manuscript (Ministerio de Educación y Ciencia).


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Centre for Ecology and Hydrology (CEH)–BanchoryAberdeenshireUK
  2. 2.Departamento de Ecología EvolutivaMuseo Nacional de Ciencias Naturales, CSICMadridSpain

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