How Early Rearing Conditions Influence Behaviour and Survival of Pheasants Released into the Wild

Abstract

Translocation programmes, particularly when using the release of a captive reared population, often fail in their efforts to create a self-sustaining population. High mortality after release is a key issue and often associated with behavioural, physiological and cognitive deficiencies between the released population and their wild counterparts. Mitigation of these deficiencies is essential for successful translocation programmes.

I showed that pheasants (Phasianus colchicus) that were reared in more naturalistic conditions early in life were better suited to the natural environment after they were released into the wild. Post release survival was improved with exposure to more naturalistic diets prior to release. We identified four mechanisms to explain this. Pheasants reared with more naturalistic diets: 1) foraged for less time and had a higher likelihood of performing vigilance behaviours; 2) were quicker at handling live prey items; 3) were less reliant on supplementary feed which could be withdrawn; 4) developed different gut morphology. Consequently birds reduced the risk of predation by reducing exposure time whilst foraging, while allowing more time to be vigilant, were better at handling and discriminating natural food items and not solely reliant on supplementary feed and had a better gut system to cope with the natural forage. Post release survival was also improved when pheasants were reared with access to perches.  We identified three mechanisms to explain this. Pheasants reared with access to perches had: 1) a physiology to better enable the birds to fly to the higher branches and cope with prolonged roosting; 2) a higher propensity to roost off the ground at night; and 3) more accurate spatial memory. Consequently, birds were at a reduced risk of terrestrial predation by roosting at night, and accurately remember their new environment upon release. I also showed that these manipulations did not compromise the welfare of the individuals prior to release, as often feared when trying to create a naturalistic environment to a captive population.

An additional mechanism that can affect the success of a translocation programme, operating at the level of the population, considers the optimality of the mixture of released individuals that can influence a release programme. The personality of birds within a released population, tested prior to release into the wild, influenced their fate and dispersal.  I suggest a number of release mechanisms that would aid the survival of a diverse range of behavioural types that are essential for the production of a self-sustaining population in a fluctuating environment.

I showed that harem size is strongly influenced by the vigilance behaviour of its constituent members. Despite a shared interest in increasing harem size, their optimal size is influenced by trade-offs in individual vigilance behaviour, resulting in relatively small harems, perhaps leading to females associating with less preferred males, and males being surrounded by fewer females than they could mate with. The aim of this study was to provide the background to future work trying to promote developments to allow for better reproductive success.

I finally discussed these results and how they add to the current knowledge of captive-rearing and release, and examine the wider implications of my results from the pheasant rearing system for reintroduction biology. I calculate the likely costs of interventions and extrapolated the potential economic and environmental benefits of implementing changes to the current methods of rearing.