The demography of an increasing insular Eurasian Scops Owl ( Otus scops ) population in western France
Résumé
Rapid population declines of many long-distance Afro-Palaearctic migratory bird species
are ongoing across Europe but the demographic drivers are often poorly understood,
thereby limiting the development of appropriate conservation actions. Using long-term
population monitoring (39 years), capture–mark – recapture data and a matrix m odel, we
estimated demographic parameters and the effect of climate variables on adult survival,
and modelled the dynamics of an increasing population of Eurasian Scops Owls Otus
scops in a landscape with agric ultural abandonment in western Fra nce. The observed
mean annual population growth rate was 1.055 (from 68 to 523 territorial males
between 1981 and 2019). Over the study period, clutch size and hatching success were
stable, but edging success and breeding success showed slight negative trends, probably
due to density-dependence. Survival varied with age , with an increase during early life
and evidence for rapid senescence from 4 years old. Adult survival remained stable and
was positively linked to the amount of autumn rainfall in the Sahel and to the winter
North Atlantic Oscillation. Survival of younger age-classes made the largest contribution
to the variance of the population growth rate, followed by clutch size, edging success
and survival of older birds. Such a long-term population increase in a landscape where
intensive agriculture has decreased by 64.6% sheds some new light on the causes of the
decline of European Scops Owl and other Afro-Palaearctic bird populations. We infer
some of the possible causes of this large-scale decline, in particular food shortage, and
discuss conservation measure s that could be applicable to reverse this trend.