In wild vertebrates, young parents are less likely to successfully rear offspring relative to older ones because of lower parental skills (‘the constraint hypothesis’), lower parental investment (‘the restraint hypothesis’) or because of a progressive disappearance of lower-quality individuals at young ages (‘the selection hypothesis’). Because it is practically difficult to follow an offspring during its entire life, most studies have only focused on the ability of individuals to breed or produce young, while neglecting the ability of such young to subsequently survive and reproduce. Several proxies of individual quality can be useful to assess the ability of young to survive and recruit into the population. Among them, telomere length measurement appears especially promising because telomere length has been linked to longevity and fitness in captive and wild animals. By sampling 51 chicks reared by known-aged parents, we specifically tested whether parental age was correlated to offspring telomere length and body condition in a long-lived bird species, the Black-browed Albatross (Thalassarche melanophrys). Young Black-browed albatrosses produced chicks with shorter telomere relative to those raised by older ones. Short offspring telomeres could result from poor developmental conditions or heritability of telomere length. Moreover, young parents also had chicks of lower body condition when compared with older parents, although this effect was significant in female offspring only. Overall, our study demonstrates that parental age is correlated to two proxies of offspring fitness (body condition and telomere length), suggesting therefore that older individuals provide better parental cares to their offspring because of increased parental investment (restraint hypothesis), better foraging/parental skills (constraint hypothesis) or because only high-quality individuals reach older ages (selection hypothesis).

Whole organism metabolism is an integrative process that determines not only the energy cost of living but also the energy output that is available for behavioral and physiological processes during the life cycle. Developmental challenge is known to affect growth, development of several organs, and several physiological mechanisms (such as HPA responsiveness, oxidative stress or immunity), which may altogether affect adult metabolism. All these developmental effects are likely to be mediated by glucocorticoids but the impact of developmental glucocorticoid exposure on adult metabolism has rarely been studied and the results are equivocal. In this study, we examined the impact of developmental exposure to corticosterone (CORT, the main avian glucocorticoid hormone) on RMR (resting metabolic rate, measured in thermoneutrality, 25°C) and TMR (thermoregulatory metabolic rate, measured in cold challenging condition, 5°C) in the House sparrow. Following experimental administration of CORT at the nestling stage, house sparrows were kept in captivity until adulthood when their metabolism was measured. We found that post-natal CORT exposure decreased both RMR and TMR in adult sparrows. This CORT-mediated reduction of metabolism was also associated with a reduced overnight body mass loss. Therefore, our results suggest that developmental CORT exposure can orient the phenotype towards an energy-saving strategy, which may be beneficial in a constraining environmental context.

Among the pressures introduced by urbanization, artificial light at night (ALAN) can be problematic, particularly for nocturnal species. Populations of European hamsters (Cricetus cricetus) have dramatically decreased in France since 1972 because of habitat loss due to urbanisation and changes in agricultural methods. The conservation project Life Alister aims to increase the abundance of this species in suburban areas via hamster release. However, the success of this population-restoration project may be compromised due to the possible effects of ALAN on the daily and seasonal cycles and behaviour of this nocturnal species. To understand how hamsters may respond to relocation, we experimentally studied the impact of ALAN on hamster foraging, a decisive behaviour for survival in natural habitats. This study assessed the behavioural responses of 18 animals when choosing between two food sources of different palatability in two different lighting conditions: artificial light (4 or 40 lux) or darkness. Our results show that hamsters avoided lighting that mimics suburban streetlights, particularly when grooming. Moreover, this study reveals that hamsters do not avoid street-lit areas when highly palatable food is present, suggesting they would be more susceptible to predation under these circumstances. Our results suggest that the adverse effects of ALAN on the behaviour of hamsters released on the outskirts of developed suburban areas could be limited by restricting the number of street lights, moderating the intensity of street lighting, or switching lights off during the hours hamsters are most active. We further recommend that wildlife managers avoid planting plants that are highly palatable to hamsters close to lighting in suburban areas to limit the risk of predation for this species.

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