West African Mangroves Harbour Millions of Wintering European Warblers

Abstract

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Conditions at autumn stopover sites affect survival of a migratory passerine

“…Data on wintering sites obtained from the Polish Ringing Centre in Gdańsk, and data from nearby populations in the Czech Republic and Germany (Procházka and Policht 2008;Bairlein et al 2014) overlap and suggest that birds from our population winter in the Ivory Coast, Sierra Leone, Liberia, Ghana, Togo and Guinea, probably mostly on the coast (Zwarts et al 2014) …”

“…However, we did not find a similar relationship between survival and precipitation for spring stopover sites or wintering areas. One possible explanation for our results is that in western Africa Reed Warblers usually occupy mangrove forests (where they are the dominant species, although a few other European species, such as Common Chiffchaffs or Willow Warblers also occur; Zwarts et al 2014), which are not very sensitive to short-term fluctuations in precipitation levels. Ockendon et al (2014) also did not find a positive correlation between rainy season rainfall and mean winter NDVI for the humid zone, where Reed Warblers from central Europe (but also, for example, Willow and Garden Warblers, House Martins and Spotted Flycatchers) winter and fuel up before their spring migration (the authors did find positive correlations for the arid zone and southern Africa).…”

“…demonstrated that Reed Warbler populations breeding in neighbouring areas of Europe tend to undertake similar migration routes and have wintering grounds in the same parts of Africa. Reed Warblers from central and western Europe are known to spend their winters in western sub-Saharan Africa, probably mostly near the coast (Zwarts et al 2014). They migrate by alternating short periods of flight with longer stopovers, but they gain mass mostly at stopover sites in the Mediterranean area, just before crossing the Sahara Jenni 2000, 2001;Rguibi-Idrissi et al 2003).…”

“…These authors suggest that at this time of year the area of the park and the remaining part of western Sahel may host about 67% of the western European Reed Warbler population. According to Zwarts et al (2014) about 30-50% of the European Reed Warbler population (4-6 million birds) spend winter in mangrove habitats along the coast.…”

“…Based on recoveries and published data available for the species we considered August-October to be the time of autumn migrations; October-March as the period spent at wintering grounds; and March-May as the time of spring migrations (Cramp 1992;Korner-Nievergelt et al 2002;Balança and Schaub 2005;Zwarts et al 2014). The periods overlap as breeding, arrival and departure of individuals of the species are asynchronous (Halupka et al 2014b).…”