Effects of rearing conditions on natal dispersal processes in a long‐lived predator bird

Abstract

Natal or prebreeding dispersal is a key driver of the functioning, dynamics, and evolution of populations. Conditions experienced by individuals during development, that is, rearing conditions, may have serious consequences for the multiple components that shape natal dispersal processes. Rearing conditions vary as a result of differences in parental and environmental quality, and it has been shown that favorable rearing conditions are beneficial for individuals throughout their lives. However, the long‐term consequences of rearing conditions on natal dispersal are still not fully understood in long‐lived birds. In this study, we aim to test the following hypotheses to address the relationship between rearing conditions and certain components of the natal dispersal process in Bonelli’s eagle (Aquila fasciata): (1) The body condition of nestlings depends on the quality of the territory and/or breeders; and (2) the survival until recruitment, (3) the age of recruitment, and (4) the natal dispersal distance (NDD) all depend on rearing conditions. As expected, nestlings reared in territories with high past productivity of chicks had better body condition, which indicates that both body condition and past productivity reflect the rearing conditions under which chicks are raised. In addition, chicks raised in territories with high past productivity and with good body condition had greater chances of surviving until recruitment. Furthermore, birds that have better condition recruit earlier, and males recruit at a younger age than females. At last, although females in good body condition exhibited higher NDD when they recruited at younger ages, this pattern was not observed in either older females or males. Overall, this study provides evidence that rearing conditions have important long‐term consequences in long‐lived birds. On the basis of our results, we advocate that conservation managers work actively in the promotion of actions aimed at improving the rearing conditions under which individuals develop in threatened populations.

Phenotypic and environmental correlates of natal dispersal in a long-lived territorial vulture

“…Both variables are usually considered as good proxies of individual quality in birds, and indeed have been related to survival prospects later in life 80 , so these females probably decided voluntarily to move further. In addition, body condition may be a prerequisite for not suffering high costs during long-distance movements 81 , and may affect different aspects of the dispersal process related to landscape exploration, such as speed, tortuosity, and path length 82 . In late hatched birds, however, body condition did not appear to influence dispersal, which was shaped instead by the density of breeders in the natal population.…”

Age of First Territory Settlement of Golden Eagles Aquila chrysaetos in a Variable Competitive Landscape

“…Field observations were also typically undertaken at particular times of the year (Hardey et al, 2013;Hayhow et al, 2017). In addition, beyond nest building, young large raptors are typically less likely to reach any of the reproductive stages leading to fledging than in their later years or in older birds (Steenhof et al, 1983;Sánchez-Zapata et al, 2000;Pedrini and Sergio, 2001;Whitfield et al, 2004a;Azpillaga et al, 2018;Murgatroyd et al, 2018). Hence our analytical cut-off date could also reduce the availability of field evidence of egg-laying through to fledging, i.e., for young eagles which settled on a territory late in the study period there was a lower likelihood of field recording of reproductive activities beyond nest building.…”

“…When modelling population dynamics, first territory settlement represents recruitment of dispersing birds to the prospective breeding population (Azpillaga et al, 2018) which affects measures of occupied territories and a population's breeding productivity (Hayhow et al, 2017;Steenhof et al, 2017;Gjershaug et al, 2018). Age of first territory settlement (AFTS) is therefore an important variable in understanding several features of large raptor populations, not just NDD estimates.…”

Post‐release dispersal and breeding site suitability of reintroduced populations of the Crested Ibis in Shaanxi Province, China

“…Our results indicated that in Ningshan County, Crested Ibises often forage in the paddy fields on both sides of the Chang'an River, where most of the nest sites exist. In addition, the natal dispersal of wild Crested Ibises and long‐lived raptors is associated with the distribution pattern of foraging places (Yu et al 2010; Azpillaga et al 2018). Thus, the distribution of foraging sites is one of the most important determinants of Crested Ibis breeding site selection in Ningshan County.…”