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

Jesus Martinez-Padilla, Juan A. Fargallo

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16 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)1735-1742
Number of pages8
JournalBehavioral Ecology and Sociobiology
Issue number11
Early online date10 May 2007
Publication statusPublished - Sept 2007


  • Falco tinnunculus
  • food supplementation
  • egg mass
  • sex investment
  • sexual size dimorphism
  • sexually dimorphic birds
  • black-headed gull
  • sibling competition
  • falco-tinnunculus
  • hatching asynchrony
  • seasonal decline
  • nestling growth
  • clutch size
  • facultative manipulation
  • brood reduction
  • Falco tinnunculus
  • food supplementation


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