Chough (Pyrrhocorax pyrrhocorax) Science Article 3
abstract
Identifying which age-specific demographic rates underlie variation in a population’s growth rate (?) is an important step towards understanding the population’s dynamics. Using data from a 20-year study of marked individuals, we describe patterns of demographic variation and covariation in the Scottish red-billed chough population (Pyrrhocorax pyrrhocorax), and investigate which demographic rates have the greatest projected and realized influence on ?. Survival, the probability of breeding and breeding success varied with age in this population. Data were sufficient to estimate year-specific probabilities of first-year, second-year and adult (all ages over 2) survival and mean breeding success. A population trajectory modelled using these parameter estimates closely matched census data, suggesting that estimates and simplifying assumptions were sufficient to accurately describe important demographic processes. Elasticity analyses based on stage-classes for which year-specific survival was estimable suggested that ? was more elastic to variation in adult survival than first- or second-year survival or breeding success. These ranks were consistent across all 15 years for which ? could be estimated directly, although the elasticity of adult survival declined with population growth.
J. M.Reid, E. M.Bignal, S.Bignal, D. I.McCracken and P.Monaghan, Journal of Animal Ecology 73 (4), 777-788