The influence of risk factors associated with captive rearing on post-release survival in translocated cirl buntings Emberiza cirlus in the UK

K. Fountain,S. Croft,C. Jeffs,I. Carter,A. W. Sainsbury,J. Gregson,A. Evans,J. Lister,Y. M. Chang

doi:10.1017/s0030605315001313

Abstract

AbstractPopulation decline resulting from agricultural intensification led to contraction of the range of the cirl bunting Emberiza cirlus in the UK to a small area of south Devon. As part of the UK Biodiversity Action Plan for the species, a project to re-establish a population in suitable habitat in Cornwall was undertaken during 2006–2011, in which chicks were removed from the nest in Devon, hand-reared and then delayed-released. The survival of the birds to four time points in the year after release was analysed in relation to the effect of rearing factors, using a multivariable logistic regression model. Individuals with higher body weight at capture were more likely to survive to 1 January and 1 May in the year following release, and individuals released in June and July were more likely to survive than those released in August. Individuals released in 2006 and 2011 had a higher survival rate than those released during 2007–2010. Timing of capture, time spent at each stage in captivity, medication and the detection of parasites in the brood had no significant effect. Immunosuppressive disease, weather factors and predator activity may have led to some of the observed differences in survival. This analysis provides evidence with which to plan future translocation projects for cirl buntings and other passerine birds.

Highlights

Conservation programmes involving the release of captive-reared animals have had varying degrees ofC
Post mortem examination Birds found dead post release were examined according to standard avian post-mortem procedure (Latimer & Rakich, ), with tissues examined where appropriate by histology, bacteriology and virology
At the planning stage of the project, projections of the expected post-release survival of the cirl buntings were made based on intensive monitoring of wild birds over many years

Summary

Introduction

Stress is often cited as a factor affecting the success of avian conservation activities (Teixeira et al, ), and captivity is the critical factor that induces a significant and prolonged loss of the negative feedback mechanism of the stress response axis (Dickens et al, ) This renders released birds less able to cope with acute stressors in the wild and may blunt the normal flight response for evasion of predators. The cirl bunting Emberiza cirlus, a sedentary passerine, is categorized as Least Concern on the IUCN Red List on the basis of its extensive range throughout south and western Europe (BirdLife International, ) It was once widespread at the northern edge of its range, in the UK, but suffered dramatic declines in the th century as a result of changes in farming methods, such as the removal of.

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