Aves, p�le ornithologique de Natagora

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Aves, 38/2 | 2001 | 69-76

  Variation of Tengmalm's Owl (Aegolius funereus) sex ratio in nest.
Robert, H. & Sorbi, S.

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Article summary

Among some species, the sex ratio adaptability may be due to evolutive physiological strategies, or to different mortality rates after birth. The species showing a sexual dimorphism marked by differences of weight, and therefore with different energetic needs, are interesting subjects for the sex ratio studies. The Tengmalm's Owl sex ratio in the nest, in Haute Ardenne (Belgium), has been studied through the DNA analysis of blood sampling, using the technic of PCR (Polymerase Chain Reaction). 31 blood samples revealed a sex ratio of 15 males and 16 females. A similar study lead in Sweden mentions a sex ratio of 65% of males and 35% of females. An hypothesis to explain this difference can be that in Scandinavia, the males have to resist to hard winter conditions to defend their territory, and have a higher mortality rate, whereas the females are nomad. In our more tempered regions, the males do not meet the same climatic constraints. These differences in the sex ratio seem to coroborate Bull's theory, that the sex ratio can vary according to specific environment conditions.

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