Disentangling the effects of environmental conditions on wintering and breeding grounds on age-specific survival rates in a trans-Saharan migratory raptor

Migratory species are subject to environmental variability occurring on breeding and wintering grounds. Estimating the relative contribution of environmental factors experienced sequentially during breeding and wintering, and their potential interaction, to the variation of survival is crucial to predict population viability of migratory species. Here we investigated this issue for the Montagu's harrier Circus pygargus, a trans-Saharan migrant. We analysed capture-recapture data from a 29-yr long monitoring of wing-tagged offspring and adults at two study sites in France (Rochefort-RO & Maine-et-Loire-ML). The study period covers a climatic shift occurring in the Sahel with increasing rainfall following a period of droughts (Sahel greening). We found that harriers’ adult survival in RO (between 1988 and 2005) varied over time and was sensitive to the interaction between the amount of rainfall in the Sahel and the annual mean breeding success, two proxies of prey availability. The oc...