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Oecologia

, Volume 137, Issue 1, pp 140–147 | Cite as

Ural owl sex allocation and parental investment under poor food conditions

  • Jon E. BrommerEmail author
  • Patrik Karell
  • Tuomo Pihlaja
  • Jodie N. Painter
  • Craig R. Primmer
  • Hannu Pietiäinen
Behavioural Ecology

Abstract

Parents are expected to overproduce the less costly sex under poor food conditions. The previously regular 3-year cycle in the abundance of voles, the main prey of the Ural owl, Strix uralensis, temporarily disappeared in 1999–2001. We studied Ural owls' parental feeding investment and sex allocation during these poor-quality years. We sexed hatchlings and embryos in unhatched eggs of all 131 broods produced during these years. Population wide, the owls produced significantly more males (56%). The parental food investment in the brood was estimated by sorting out the prey remains in the bottom of nest boxes. Food delivered to 83 broods without chick mortality showed no clear sex-specific investment. Nestling mortality was equal in both sexes. Thus, evidence for an investment-driven sex allocation is weak. Neither laying date, brood size nor the female's condition correlated with offspring sex ratios. In these poor years, parents provided less food per chick and the fledging weight of daughters was reduced more than the weight of sons compared with years of high food abundance (1983 and 1986). We discuss, in relation to published studies, the possibility of a sex-allocation scenario where, under poor food conditions, a daughter's long-term fitness is reduced more than a son's.

Keywords

Life history Sexual dimorphy Sex ratio Vole cycle 

Notes

Acknowledgements

The committee for animal experiments (Helsinki University) gave permission to sample Ural owl offspring. We thank Marianne Fred, Jenni Punttila and especially Heikki Kolunen for assistance in the field and all landowners for permission to work on their land. Hans Breeuwer kindly helped in the early stages of DNA sexing. We thank Patrik Byholm for comments and discussion. This work was financed by the Academy of Finland (H.P., C.R.P.), Division of Population Biology (J.E.B., H.P., C.R.P.), LUOVA (J.E.B.), Ehrnrooth Foundation (J.N.P.), Finnish Cultural Foundation (J.E.B.), Oskar Öflunds Stiftelse (J.E.B.) and Societas pro Fauna et Flora Fennica (J.E.B., P.K.).

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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • Jon E. Brommer
    • 1
    Email author
  • Patrik Karell
    • 1
  • Tuomo Pihlaja
    • 1
  • Jodie N. Painter
    • 1
  • Craig R. Primmer
    • 2
  • Hannu Pietiäinen
    • 1
  1. 1.Department of Ecology &and Systematics, Bird Ecology UnitUniversity of HelsinkiHelsinkiFinland
  2. 2.Department of Ecology and SystematicsUniversity of HelsinkiHelsinkiFinland

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