No abstract

The prospective behaviour for nests by conspecific intruders may be a strategy to gather public information for future reproduction or to secure resources for immediate reproduction. Although the relationship between the sex, age and breeding experience of intruders and the sex and age of residents may be crucial for understanding the significance of nest‐prospecting behaviour, a precise determination of these traits has rarely been addressed in field studies. In a free‐ranging population of spotless starlings ( Sturnus unicolor), inexperienced birds were the predominant intruders. The ratio of male‐to‐female intruders was higher among birds without previous breeding experience, although our results did not allow us to determine whether more inexperienced males or females intruded nests. The average annual rate of intrusion of either sex was strongly correlated with the number of fledglings produced in the study colony the previous year, which seems to indicate that the inexperienced intruders were, in general, yearlings. The proportion of the sexes among the intruders in each study year was correlated with the average age of male owners but not with the age of female owners. This result suggests that the presence of intruding males in the nests was affected by an increased opportunity to find vacancies in nesting territories as resident males became older. This finding supports the hypothesis that, in most cases, birds visited nests to obtain personal information about nesting resources. However, the intrusion rates were higher when there were nestlings than during the incubation period, which suggests that collecting public information was also involved in the intruding behaviour. Both sexes regularly attacked intruders, which implies that the intruders inflicted some kind of cost on the owners. Female floaters were more frequently chased, probably because they regularly lay parasitically in conspecific nests.

The habitat association approach has been increasingly used in ecology to resolve problems in wildlife conservation and management. One problem related to habitat association studies is that they are restricted to small geographical areas within a species’ range, and thus they are applicable to only a limited set of environmental conditions utilized by the species. In addition, very few studies address why the preference for specific habitat components may be adaptive for the species in question. The objective of this study was to examine how consideration of populations of a species from two dramatically different environments affects the results of habitat association modelling for a ground‐nesting passerine, the Rock Bunting Emberiza cia. At a regional scale, a trend to defending breeding habitat patches with relatively higher stone cover was confined to birds from a temperate region in Slovakia. In contrast, in a semi‐arid region in southeastern Spain, Rock Buntings preferred to use breeding habitat patches that had relatively higher grass cover. Combining data from both regions, breeding Rock Buntings showed a general pattern of using habitat patches close to hedges, with low bush cover, high ditch density and a steep slope. Whereas regional habitat association models appear to be sensitive to the particularities of the breeding environment, our study suggests that Rock Bunting breeding habitat association is constrained by the adults’ tactics to protect themselves against predators. Although the birds prefer to nest in patches of low vegetation, the better to see nearby predators, these patches are ideally close to taller vegetation that can be used to provide cover when evading predators, and they are also of a rugged profile that helps the birds to approach and leave the nest stealthily.

No abstract

The males' trade-off between caring for the offspring or investing in attracting additional mates is well established in the theory of mating systems. The reproductive consequences for males of alternative strategies adopted by them in response to these conflicting demands should depend on several ecological and social factors that may strongly vary among years. This variation, however, has been rarely addressed in field studies despite it being essential to understand the evolution of parental care in facultatively polygynous species. In the present paper, we examine the reproductive consequences of paternal vs. territorial strategies in the polygynous spotless starling (Sturnus unicolor) during four consecutive breeding seasons (1996-1999) in which the number of male defending nest boxes and several population variables such as nestling starvation rates, nest predation rates and fledgling production varied markedly. In 1996 we manipulated the propensity of males to feed their offspring by means of androgens and antiadrogens, and examined the consequences of male behaviour on reproductive success during the subsequent four breeding seasons. Males implanted in1996 with the antiandrogen cyproterone acetate (Cy-males) fed more frequently than males implanted with testosterone (T-males) or control males (C-males) both during the season in which they were implanted and in the next season. The number of nest boxes defended influenced total breeding success mainly in the years when male feeding frequency was less important for breeding success per nest. A lower proportion of Cy-males than T- or C-males still held at least a nest box in 1999, three years after they were implanted. As a result, the number of fledglings produced over the four years studied was smaller for Cy-males than for T- or C-males. These results suggest that the oscillating selective forces acting on breeding male starlings seem to operate more frequently against the development of parental care strategies, while the polygynous strategy seems to be favoured under a wide array of ecological conditions. Although increased density of potential breeders may constrain territorial expansion and polygyny, the high cost of losing a minimum breeding site may select for the maintenance of aggressive behaviour and low parental investment.