High within‐winter and annual survival rates in a declining Afro‐Palaearctic migratory bird suggest that wintering conditions do not limit populations

Abstract

For migratory birds, it is necessary to estimate annual and overwinter survival rates, identify factors that influence survival, and assess whether survival varies with age and sex if we are to understand population dynamics and thus inform conservation. This study is one of the first to document overwinter and annual survival from the wintering grounds of a declining Afro-Palaearctic migrant bird, the Whinchat Saxicola rubetra. We monitored a population of marked individuals for which dispersal was low and detectability was high, allowing accurate estimates of survival. Annual survival was at least 52% and did not differ significantly across demographic groups or with habitat characteristics or residency time in the previous winter. Overwinter survival was very high and monthly survival at least 98% at some sites. Although winter residency varied spatially and with age, lower residency did not correlate with reduced annual survival, suggesting occupancy of multiple wintering sites rather than higher winter mortality of individuals with shorter residency. Our results suggest that mortality occurs primarily outside the wintering period, probably during migration, and that wintering conditions have minimal influence on survival. The similarity between survival rates for all age and sex classes when measured on the wintering grounds implies that any difference in survival with age or sex occurs only during the first migration or during the post-fledging stage, and that selection of wintering habitat, or territory quality, makes little difference to survival in Whinchats. Our findings suggest that the wintering grounds do not limit populations as much as the migratory and breeding stages, with implications for the conservation of declining Afro-Palaearctic migrants more widely.

An experimental evaluation of the effects of geolocator design and attachment method on between‐year survival on whinchats Saxicola rubetra

“…However, analyses comparing tagged birds to equivalently large control birds gave essentially identical results. Our wider study of Whinchats shows no effects of body size (wing length and body mass at capture), and age or sex, on apparent annual survival rates (Blackburn and Cresswell ).…”

Survival of Afro‐Palaearctic passerine migrants in western Europe and the impacts of seasonal weather variables

“…Mortality during migration appears to be very high for some species (Sillett & Holmes , Klaassen et al . , Blackburn & Cresswell ), potentially limiting populations. Therefore, correlations between winter weather and annual survival may describe the effects of weather on overwintering survival or migration survival.…”

Nestling diet optimization and condition in relation to prey attributes and breeding patch size in a patch-resident insectivorous passerine: an optimal continuum and habitat constraints

“…A very recent investigation has found evidence that mortality in Whinchats occurs primarily outside the wintering period, i.e. mostly during the migratory and breeding stages; overwintering conditions thus exert a minimal influence on the survival of this declining species (Blackburn and Cresswell 2016). As a result of the socioeconomic transformation of agriculture and resulting land abandonment in Central and Eastern Europe in the last 20-30 years, Whinchats have successfully recolonized abandoned crop fields and its populations have increased considerably in certain areas (Orłowski 2004(Orłowski , 2005Tryjanowski et al 2009;Sanderson et al 2013;Shitikov et al 2015).…”