Dutch Sedge Warblers Acrocephalus schoenobaenus and West-African rainfall: Empirical data and simulation modelling show low population resilience in fragmented marshlands.

Sedge Warbler (Acrocephalus schoenobaenus) Science Article 8

abstract

Sedge Warbler populations in The Netherlands have declined dramatically over the last 25 years, especially between 1973-75 and 1982-85. Population declines correlate with yearly rainfall in the western part of the Sahel-Soudan zone, the most probable wintering area of West-European birds (after removing effects of autocorrelation, rs = 0.58). However, populations in relatively unfragmented landscape showed a clear recovery after 1984, while those in heavily fragmented landscapes showed no recovery. A spatially explicit population simulation model was used to test the general hypothesis that bird populations in fragmented landscapes show stronger declines and less resilience than populations unfragmented habitats in response to a catastrophe such as winter drought. The simulations demonstrated that in fragmented landscapes (less than 1% marshland), the relative decrease in numbers was 50% higher than in less fragmented habitats (more than 1% marshland). Furthermore, after a decrease, the recovery to initial numbers in landscapes with less than 1% marshland would take about five times longer than in areas with more than 15% suitable habitat. We tentatively conclude that Sedge Warblers breeding in fragmented marshland habitats are more vulnerable to drought events in West-Africa than those in unfragmented habitats

Foppen R., Ter Braak C.J., Verboom J. & Reijnen R., ARDEA 87 (1): 113-127

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