© Beat Rüegger
How do origin and rearing conditions affect a bird's fitness in the wild? This question was explored in the context of a Grey Partridge reintroduction scheme.
Animals are in a constant process of adaptation to their environment. Their physical condition and behaviour, called phenotype in biology, are controlled by the interplay of genetic and environmental factors. Even prenatal environmental conditions, for example food shortages during the breeding period, can have a lasting influence on development. These prenatal effects may prepare the embryo for the world awaiting it upon hatching. Depending on the conditions a chick faces in the egg or shortly after hatching, it will be better or worse equipped to meet the challenges of its later environment. The main objective of the study was to select the origin and rearing conditions of Grey Partridges in a way that best prepares them for life in the wild.
As part of a dissertation project, Grey Partridges were reared in captivity and later released in the Champagne genevoise in the Canton of Geneva. The study investigated how food availability influenced the Grey Partridges' physical development, behaviour and survival. The birds came from two different strains. Partridges from the domesticated strain had been held in captivity for more than 30 generations and had therefore adapted to life in the aviary. Partridges from the wild strain had been in captivity for only three generations, and were thus much closer to wild populations. Different environmental conditions were simulated by means of a feeding experiment. During oviposition and the first four weeks of life, parents from both strains and their offspring either had unrestricted access to food (predictable feeding), or access was restricted every day for three to four hours at different times (unpredictable feeding). This feeding experiment simulated environmental conditions that can occur in the wild, influencing the birds' development and later their survival. Partridges in these experimental groups were examined throughout the rearing period. After release, morphology, physiology, behaviour and survival were compared between the groups.
Compared to the domesticated strain, birds from the wild strain had stronger immune responses, a more pronounced hormonal stress response, and higher resistance against oxidative stress (i.e. an improved ability to break down reactive oxygen species in the body). Thus, birds from the wild strain seemed to be physiologically well equipped to survive in the wild. There were indications that unpredictable feeding of adult birds during oviposition strengthened the hormonal stress response in hatched chicks, suggesting that unpredictable conditions before hatching may improve the birds' ability to respond adequately to disturbance in the environment. Unpredictable feeding of chicks after hatching strengthened the immune response and increased the probability of survival in the wild. Mastering challenges during the rearing period could therefore be essential for success in the wild. Partridges that were quick to explore unknown territory in behavioural tests, demonstrating bold behaviour, had higher chances of survival than passive and shy birds. A bold personality may therefore be of benefit when exploring and colonising new habitats.
Grey Partridges are social birds that spend a large part of the year in so-called coveys. The studied Grey Partridge coveys differed at all levels, from physiology and behaviour to survival. Intact, stable coveys are extremely important for the survival of individuals and hence for the success of a reintroduction project.
The results show that even small changes in the environment before and after hatching can influence a bird's development and survival. Simple measures such as unpredictable feeding in captivity can increase the chances of survival in the wild and contribute to the success of reintroduction schemes.
Alexandre Roulin, Université de Lausanne