Survival in a long-lived territorial migrant: effects of life-history traits and ecological conditions in wintering and breeding areas

Abstract

Despite its key role in population dynamics and evolutionary ecology, little is known about factors shaping survival in long-lived territorial species. Here, we assessed several hypotheses that might explain variability in survival in a migratory Spanish population of a long-lived territorial species, the Egyptian vulture Neophron percnopterus, using a 16-year monitoring period and live-encounter histories of 835 individually marked birds. Cormack-Jolly-Seber captureÁrecapture models showed no evidence for effects of sex or nestling body condition on survival. However, the normalized difference vegetation index (NDVI; an indicator of primary productivity) of natal territories had positive effects on juvenile survival, indicating that environmental conditions experienced early in life can determine survival prospects. Survival increased with age (0.7390.02 in the first 2 years to 0.7890.03 in years 3 and 4) to later decrease when birds were five years old (0.6090.05), the age at which they acquire the adult plumage, abandon the communal lifestyle of juveniles, and may look for a breeding territory. At older ages, survival was higher for non-breeding (0.7590.02) and breeding adults (0.8390.02). Among the latter, birds that recruited into better territories had higher survival prospects. Age-specific variation in survival in this species may be related to behavioural changes linked to dispersal and recruitment into the breeding population, while survival prospects of adult birds strongly depend on breeding territory selection. These results suggest a tradeoff between recruiting soon, and thus reducing mortality costs of a long and extensive dispersal period, and trying to recruit into a good quality territory. Finally, annual survival rates for birds of all age classes were positively related with the NDVI in their African wintering grounds. Although this relationship was probably mediated by food availability, further research is needed to properly identify the limiting factors that are affecting trans-Saharan migrants, especially in light of global climate change.

Studying the demographic drivers of an increasing Imperial Eagle population to inform conservation management

“…Our model suggests, however, that survival in the third and fourth years may be lower than in the second year, although the estimates were surrounded by considerable uncertainty and therefore do not permit robust interpretation. However, a similar pattern has been described in other long-lived raptors where survival was lowest for the life stage when young birds first attempt to occupy a breeding territory (Grande et al 2009). We estimated that about 29 % of three year old birds and 46 % of four year old birds may start a breeding attempt.…”

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

“…In long‐lived species, survival rates during lifespans are expected to follow a nonlinear pattern and are determined by a variety of constraints and selective pressures (Grande et al., 2009; Hernández‐Matías, Real, Pradel, Ravayrol, et al., 2011; Stearns, 1992). In territorial raptors, one of the most critical stages occurs when the parents expel their fledglings from their natal territory and young birds enter into a new transient nomadic phase—the dispersal period—which in Bonelli’s eagles implies long‐distance movements to dispersal areas and no territorial behavior (Cadahía et al., 2010; Real & Mañosa, 2001).…”

“…If low‐quality territories are more easily accessible to young individuals, there may be a trade‐off between recruiting early and trying to recruit into a good‐quality territory (Grande et al., 2009; Kokko & Sutherland, 1998). Our data support the early‐breeding hypothesis, that is to say, that individuals in better body condition—that also may be individuals of superior quality—are more successful when competing for a vacancy and therefore recruit earlier (Figure 6).…”

“…Less is known about the mid‐ and long‐term effects of rearing conditions on long‐lived species (Szostek & Becker, 2015), which include the complex set of processes that, together, conform natal dispersal, such as the probability of surviving until recruitment, that is, the entry of prebreeding birds into the breeding portion of the population (Green & Cockburn, 2001; Hernández‐Matías et al., 2010), the age at which individuals recruit (Acker et al., 2018; Grande et al., 2009; Hernández‐Matías, Real, Pradel, Ravayrol, Vincent‐Martin, 2011; Kokko & Sutherland, 1998), and the distance from the place of birth to the recruitment site, the so‐called natal dispersal distance (NDD) (Rémy et al., 2011; Stamps, 2006). This gap in our knowledge is understandable given that effects of rearing conditions are less pronounced during middle and late life stages (Van De Pol et al., 2006).…”

Integrating effects of supplementary feeding, poisoning, pollutant ingestion and wind farms of two vulture species in Spain using a population viability analysis

“…No Allee effect was considered (A = 0), given that it has not been reported in the literature. Age-specific mortality rates were taken from the literature (Sarrazin et al 1994;Sarrazin and Legendre 2000;Le Gouar et al 2008;Grande et al 2009; Table 1). Due to the absence of site-specific mortality rates available in the literature, they were considered the same for all populations without sex differences.…”