Partial migration and decreasing migration distance in the Hungarian population of the Common Blackbird (Turdus merula Linnaeus, 1758): Analysis of 85 years of ring recovery data

The Common Blackbird is a partial migrant throughout much of its range in Europe. That is, part of its breeding population migrates while the rest stays at the breeding ground for winter. Given the rapidly changing global climate, it is important to understand how migratory birds, including partial migrants, respond to shifting climatic conditions. In this study, I analyzed 85 years of ring recovery data of the Hungarian population of the Blackbird, ringed during the breeding season and recovered during migration or winter, with two objectives in mind: (1) to assess whether the Hungarian Blackbird population is also partially migratory, and (2) to test the prediction that Blackbirds have exhibited decreasing migration distances over the past decades as expected based on warming winter temperatures. Hungarian Blackbirds expressed both migratory and resident strategies, thus can be considered as partial migrants. Furthermore, Blackbirds had been recovered increasingly closer (-5.9 km/year) to their breeding grounds in the past decades. Age and sex had no effects on recovery distance. Provided that this trend continues, the adaptive benefits of migratory behavior may eventually be reduced to a level that selection will not maintain it in the population and the Hungarian population becomes entirely sedentary. Surprisingly, 88% of migrant recoveries were the result of shooting or hunting activities in Mediterranean countries, primarily in Italy, highlighting both the need to understand the effects of hunting pressure on migratory behavior at the population level in songbirds and the urgency to ban the killing of migratory birds in European countries.