|
Vol. 47 No. 1, 2008
Parity in Fledging Sex Ratios in a Dimorphic Raptor, Montagu's Harrier Circuspy gargus
Meritxell Genovart1,*, Martín Surroca2, Alejandro Martínez-Abraín1, and Juan Jiménez3
1Population
Ecology Group, Institut Mediterrani d , Estudis Avançats IMEDEA
(CSIC-UIB), Miquel Marquès 21, 07190 Esporles, Balearic Islands, Spain
2Centro de Recuperacion de Fauna “ Forn del Vidre ” , Carretera La Sènia-Fredes (Generalitat Valenciana), Castellón, Spain
3Servicio
de Conservación de la Biodiversidad, Conselleria de Territori i
Habitatge, Generalitat Valenciana, C/ Francisco Cubells, 7, 46011
Valencia, Spain
Meritxell Genovart, Martín Surroca, Alejandro Martínez-Abraín, and Juan Jiménez (2008)
We analyzed sex ratios of 809 fledglings from 285 broods of Montagu's
Harrier (Circus pygargus) in a population located in Castellon (on the
northeastern Iberian Peninsula) in the period 1996-2005.
Montagu's Harrier females are about 15% larger than males, and
according to Fisher's theory, a bias in the secondary sex ratio towards
the cheaper (smaller) sex should be expected. This was previously
found in another population of the same species. However, overall
brood sex ratios in the present population did not depart from parity
during the study. Additionally we analyzed offspring sex ratio
variations among different years and 4 breeding areas, and although the
sex ratios did not show the same trends, differences were not
statistically significant. Results suggest 2 non-mutually
exclusive explanations: 1) the growth of females (the larger sex) might
not necessary imply greater energy requirements and 2) environmental
(e.g., food availability) and demographic variables (e.g., age of
recruitment) may vary among populations and differentially affect
offspring sex ratios. Nevertheless, although the sample size for
the overall sex ratio was large enough in our study, it was reduced
when analyzing this parameter in different years and breeding areas,
and such power constraints may have precluded detecting sex ratio
deviations from parity in space and time.
Key words: Fisher's theory, Sex allocation, Avian.
*Correspondence: Tel: 34-971-611756. Fax: 34-971-611761. E-mail:m.genovart@uib.es
|
