Influence of Natal Experience on Nest-Site Selection by Urban-Nesting Cooper's Hawks

Abstract: Exposure to environmental features early in life potentially can influence the kinds of places animals select to live later in life. We examined whether there is evidence that Cooper's hawks (Accipiter cooperii) hatched in an urban environment choose sites with features similar to their natal areas when they nest for the first time. The features we examined were the nest tree species and the level of development surrounding the nest tree. We banded nestling and fledgling Cooper's hawks in Tucson, Arizona, USA, from 1994 to 2004. We then monitored nests in Tucson to identify hawks that had been hatched in the city and eventually secured a breeding site. Percent cover of buildings around first breeding nests was not related to percent cover of buildings around natal nests for either sex. There was some evidence that being hatched in a particular tree species influenced choice of tree species at first breeding sites for males, but the influence was weak. In contrast, tree species in which first-time breeders built their nests, and the sites where the trees were located relative to development, were proportional to what was available in the Tucson metropolitan area. Our data suggest that natal experience played a limited role in nest-site selection by Cooper's hawks in Tucson for the features we examined. If learning occurred, it could have been for the general structure of natal sites. Thus, any small grove of large trees planted in Tucson could be used as a nest site by Cooper's hawks regardless of the level of development surrounding the nest.     

Temporal patterns of territory settlement and detectability in mated and unmated Nightingales Luscinia megarhynchos

In many bird species the sex ratio of adults is male-biased, which is likely to have consequences for the ecology as well as for the conservation of a species. For example, when some males remain unpaired in a population, there should be strong selection on behavioural traits that enhance pairing success. A surplus of males is also likely to have important implications for the interpretation of breeding bird survey data. In our study population of Nightingales Luscinia megarhynchos , about half of the males stayed unpaired, suggesting that the number of males encountered singing was greater than the number of breeding pairs. Furthermore, the detectability (the probability of encountering a male singing) of mated males was only two-thirds that of unmated males when censused in the morning or late in the breeding season. The relative detectability was more similar early in the season and during the twilight periods before sunrise and after sunset. Males that arrived earlier on the breeding grounds were more successful in attracting a mate than males arriving later. Some of the unmated males deserted their territories and prospected areas up to 4000 m distant, whereas others settled on the study site only late in the season and may actually have changed territories. We suggest that adult sex ratios and the time of the census should be taken into account when interpreting the results of breeding bird surveys.