Age‐related variation and temporal patterns in the survival of a long‐lived scavenger

Abstract

Although senescence has been described for various fitness components in a wide range of animal species, few studies have studied senescence in long‐lived species, and little is known about its interactions with varying environmental conditions. Using a 32 year capture–mark–recapture dataset on the griffon vulture Gyps fulvus, we examined the demographic patterns of actuarial senescence and the patterns of year‐to‐year variation in survival rates. We found a significant, surprisingly late, decrease of annual survival probabilities from the age of 28 years onward and divided individual lifetimes into to three categories (juvenile, mid‐age and senescent birds). In agreement with the environmental canalization hypothesis, our analyses uncovered 1) higher temporal variation of annual survival probabilities in both the juvenile and senescent age classes compared to the mid‐age class and 2) low sensitivity of the population growth rate to the survival of both the juvenile and senescent age classes. Our results further suggested that the temporal variation in the survival of senescent birds might be related to intra‐annual changes in air temperature amplitudes. Finally, using population dynamics modeling, we revealed contrasting effects of the inclusion of the senescent age class on predicted population growth, depending on how survival rates were modeled. Altogether, our results demonstrate the existence of a class of senescent birds that exhibit distinct demographic properties compared to juvenile and mid‐age classes.

Sex- and age-dependent patterns of survival and breeding success in a long-lived endangered avian scavenger

“…Importantly, female Egyptian vultures in our study population showed an alarmingly low local survival in comparison with the survival rates estimated for adults breeding in other European populations and other large body-sized scavengers83738. Higher rates of female mortality as that found here have been claimed as the main factor leading to male-skewed adult sex-ratios in many bird species with balanced sex-ratios at birt39.…”

“…Later in life, a decrease in survival (or reproductive success) at advanced ages (i.e., senescence9) was not detected for any sex. It is possible that the study period was relatively short with respect to the species’ potential longevity (captive birds survived up to 37 years22), or that sample size for very old individuals was small and senescence in long-lived birds has usually been detected very late in life821. It seems also reasonable that the relatively high rates of mortality of breeding adults detected here would preclude the appearance or detectability of senescence traits in our study population.…”

“…However, recent studies on long-lived birds indicate a very late life senescence (e.g. refs 8 and 9, which could also be masked by the selective disappearance of certain phenotypes among the older age-classes1). …”

Factors affecting population regulation of a colonial vulture

“…This suggested that factors compatible with IAH operate mainly at these scales, and excluded the possibility of food limitations predominating, as foraging ranges are larger than these scales and there was no support for the IAH at larger scales. Adverse weather conditions may force vultures to reduce their foraging area and concentrate foraging activity over fewer days (Monsarrat et al 2013), in addition to increased thermoregulation costs, which may affect survival and long-term fitness (Chantepie et al 2016). In territorial birds, as population density increases, an increasing proportion of animals are displaced into low-quality sites, leading to reduced fecundity or survivorship (Gill et al 2001).…”

“…even those of the lowest quality not used in other years, and the negative effect of rainfall. Adverse weather conditions may force vultures to reduce their foraging area and concentrate foraging activity over fewer days (Monsarrat et al 2013), in addition to increased thermoregulation costs, which may affect survival and long-term fitness (Chantepie et al 2016). Moreover, the presence of eyries in a cliff is a powerful attractant for conspecifics which use non-social cues for breeding (Erckmann et al 1990, Mateo-Tom as & Olea 2011.…”