Proximate and ultimate causes of natal dispersal in the great bustard Otis tarda |
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Authors: | Alonso J C; Martin E; Alonso J A; Morales M B |
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Institution: | aDepartamento de Ecología Evolutiva Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain
bDepartamento de Biología Animal, Facultad de Biología, Universidad Complutense 28040 Madrid, Spain |
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Abstract: | Between 1991 and 1997 we studied the offspring independenceand juvenile dispersal in a wild population of great bustards(Otis tarda). Young males were independent and began their juveniledispersal at an earlier age (611 months) than young females(815 months). The juvenile dispersal period was longerand the distances reached farther in males than in females.Natal dispersal distances were also longer in males, all ofwhich dispersed from their natal areas and established as adultsat 565 km from their natal nests. In contrast, most femaleswere strongly philopatric, settling at 0.55 km from theirnatal nests. These marked sex differences in offspring independenceand dispersal may have evolved originally to maintain geneticdiversity and are probably reinforced through male competitionfor mates. Young males that had fed at higher rates and receivedmore feedings from their mothers during the early maternal dependenceperiod became indepthdent and tended to disperse earlier. Theyalso integrated earlier into adult male flocks and settled earlierat their definitive leks, which were closer to their natal sites,in areas of higher adult male density. None of these correlationswas found among young females. These results suggest that enhancedfood intake and maternal care of male offspring are vitallyimportant in increasing their competitive ability during theimmature period and probably also in their fitness as breedingadults. These results are in accordance with the selective valueof large size in males and suggest how this species might havereached such a marked sexual dimorphism in size. |
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Keywords: | dispersal great bustard natal dispersal ontogenetic switch hypothesis Otis tarda proximal and ultimate causes sex differences |
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