Survival of British Sedge Warblers Acrocephalus schoenobaenus in relation to west African rainfall

Abstract

Fluctuations in the population levels and annual adult survival rates of British Sedge Warblers Acrocephalus schoenobaenus since the late 1960s are strongly correlated with indices of wet season rainfall in the west African winter quarters. Population changes are unrelated to estimates of breeding productivity in the previous year. Habitat availability in the winter quarters has probably been the main factor limiting the size of the Sedge Warbler population in Britain during the period of study.

Conditions at autumn stopover sites affect survival of a migratory passerine

“…As a result, Reed Warblers are very sensitive to the prevailing environmental conditions at important stopover sites. Our results are in line with those reported in numerous earlier studies of various avian species that provide evidence for relationships between survival and/or population levels and indices of wet season rainfall at wintering areas (Peach et al 1991;Baillie and Peach 1992;Schaub et al 2005, García-Pérez et al 2014Ockendon et al 2014;Johnston et al 2016) or along migratory routes (LaManna et al 2012). However, we did not find a similar relationship between survival and precipitation for spring stopover sites or wintering areas.…”

“…Its effects may be both direct (adverse conditions and increased metabolic rates during migration) or indirect (e.g. manifested through changes in food abundance) (Newton 2006;Peach et al 1991). However, despite the importance of the effect of weather conditions on survival during various periods of the avian annual cycle, this aspect of avian life-history has received relatively little attention and remains poorly understood.…”

“…Most studies on the annual survival of migratory birds have found that survival largely depends either on factors that affect the breeding Robinson et al 2010;Blomberg et al 2013) or wintering grounds (Peach et al 1991;Baillie and Peach 1992;Leyrer et al 2013;Salewski et al 2013;Woodworth et al 2017). Nevertheless, a growing number of studies suggest that conditions encountered during migration may also be important for some species (Stokke et al 2005;Newton 2006;Bayly et al 2011), with a few studies providing evidence that mortality during migration may be higher than that experienced at the stationary stages (Ward et al 1997;Sillett and Holmes 2002;Klaassen et al 2014).…”

The first 50 years of the North American Breeding Bird Survey

“…Therefore, understanding demographic rates that directly influence population growth, such as productivity (often measured by the capture rate of young birds, or the ratio of young birds captured to adults), is important. Species can also exhibit declines despite the availability of high-quality breeding habitat, because limiting factors on the nonbreeding grounds may also affect breeding season abundance (Peach et al 1991, Szép 1995, Wilson et al 2011) and reproductive success (Norris et al 2004, Saino et al 2004, Rockwell et al 2012) of migratory bird species. Linking local productivity to abundance trends may provide insight into the proximate demographic causes underlying population change.…”

Climatic effects on breeding grounds are more important drivers of breeding phenology in migrant birds than carry-over effects from wintering grounds

“…Climate on wintering grounds has been demonstrated to affect overwinter survival of some species [2,3], while changes in abundance of other species have been attributed to climate change on breeding grounds [4].…”