Natal dispersal in great bustards: the effect of sex, local population size and spatial isolation

Abstract

Summary 1.We investigated the causes of natal dispersal in four Spanish areas where 35 breeding groups of the polygynous great bustard Otis tarda were monitored intensively. A total of 392 juveniles were radio-tracked between 1991 and 2006 by ground and via aeroplane to avoid potential biases derived from the non-detection of long-distance dispersers. 2. We explored 10 explanatory variables that were related to individual phenotypic features, habitat and conspecific traits in terms of group size and breeding performance, and spatial distribution of available breeding groups. Probability of group change and natal dispersal distances were investigated separately through multifactorial analyses. 3. Natal dispersal occurred in 47·8% of the birds and median natal dispersal distance of dispersers was 18·1 km (range 4·97-178·42 km). Sex largely determined the dispersal probability, with 75·6% of males being dispersers and 80·0% of females being philopatric, in contrast to the general pattern of female-biased dispersal found in most avian species. 4. Both the frequency of natal dispersal and dispersal distances were affected by the spatial distribution of breeding groups. More isolated groups showed a higher proportion of philopatric individuals, the effect being more evident in males than in females. This implies a reduction in gene flow in fragmented populations, as most genetic exchange is achieved through male dispersal. Additionally, dispersers hatched in more isolated groups tended to exhibit longer dispersal distances, which increases the associated energetic costs and mortality risks. 5. The dispersal decision was influenced by the number of conspecifics in the natal group. The individual probability of natal dispersal was related inversely to the size of the natal group, which supports the balanced dispersal model and the conspecific attraction hypothesis. 6. Overall, our results provide a good example of phenotypic plasticity and reinforce the current view that dispersal is an evolutionary complex trait conditioned by the interaction of individual, social and environmental causes that vary between individuals and populations.

Genetic diversity of the great bustard in Iberia and Morocco: risks from current population fragmentation

“…Although adult birds, and particularly females, are strongly philopatric to their traditional breeding sites, the different groups are connected genetically through natal dispersal, at least at a regional scale. Natal dispersal is strongly male-biased in this species (Alonso et al 1998;Martín et al 2002Martín et al , 2008, with most juvenile males (ca. 75%) establishing as breeding adults at sites different from their natal ones, whereas 80% of juvenile females are philopatric.…”

Great Bustard (Otis tarda) nest locations in relation to leks

“…Overall, previous research and our study suggest that females of most lekking birds tend to nest close to the leks where they spend the mating period, but many of them nest at far distances, closer to other leks, perhaps looking for free space to nest. The prevalence of nest-site and lek-site fidelity among these species, and, in the case of Great Bustards, also the significantly shorter natal dispersal distances in females as compared to males (Alonso et al 1998;Martín et al 2008), supports the idea that the nesting dispersion pattern represents an evolutionary stable strategy that is more dependent on optimal dispersion and cultural transmission of nesting areas from mothers to daughters, rather than on factors related to density-dependent disturbances or predation risks at leks (lek avoidance hypothesis). As for the conservation implications, our study shows that protecting our defined lek areas, i.e., where birds are present during the mating period, would be the most important step, since this would include ca.…”

Faecal sexual steroids in sex typing and endocrine status of great bustards

“…Male flocks disperse in late March to start sexual exhibitions and are visited by females that inspect them and select one to mate with . Besides agriculture intensification and habitat fragmentation, the population recovery and distribution in Spain are also limited by factors such as their sexually biased dispersal, conspecific attraction and sex-biased mortality (Martín et al 2008;Martín et al 2007). Therefore, sex ratio and other sex-related population traits are of particular importance when assessing the conservation status of this species .…”