Is the Eurasian Reed WarblerAcrocephalus scirpaceusa Regular Wintering Species in the Iberian Peninsula? Ringing Data Say Yes

Abstract

Recent climate change is frequently invoked as the cause of changes in phenology and distances of migration. Birds are expected to reduce the length of migration in response to milder climatic conditions, and during the last years, there are a growing number of records of European long-distance migrants wintering in the Iberian Peninsula. For this reason, we have used in this study the available ringing and recoveries data for the Eurasian Reed Warbler in the Iberian Peninsula during winter, spanning 1959–2015. We show that during the last decades this insectivorous species occurs regularly during winter in South-western Europe, which could be related to the recent climate change. Some Iberian birds wintered in breeding areas, or nearby, which could indicate a potential process of sedentarization, while Eurasian Reed Warblers from Central and Northern Europe shortened the migration distance avoiding the crossing to Africa. Iberian wintering grounds seemed to be related to the origin of the birds, with British Eurasian Reed Warblers staying more northerly that individuals from Central Europe, and Eastern birds showing a tendency to winter on the Mediterranean coast. Our results support the contemporary trend of migrants overwintering at higher latitudes. Despite the considerable increase of wintering records during the last decades, we cannot confirm a real expansion because there has been an increase in ringing activity over the study period. Nevertheless, the presence of this species has become consistent during winter in well-sampled areas where it was absent in the past. With warmer winters we expect changes in the migratory system, and also an increase in frequency of long-distance migrants that avoid the crossing of the Mediterranean and the Sahara desert to remain in southern Europe during cold months.