Breeding performance of Common Blackbirds Turdus merula in two habitats with contrasting abundance trends: woodland and urban areas

This publication is part of the project ‘Preparing for vector-borne virus outbreaks in a changing world: a One Health Approach’ (NWA.1160.1S.210) which is (partly) financed by the Dutch Research Council (NWO).

Authors: Chris A.M. Van Turnhout, Bernice Goffin, Jurrian van Irsel

Abstract

After a long period of increase, the Dutch breedingpopulation of the Blackbird stabilized from the 1990s onwards, with large variation between habitats. Particularly in urban areas, and in woodlands in the northern part of the country, the numbers have declined markedly. Since reproductive data are scarce, we collected data on breeding performance in 2021 and 2022 as part of the ‘Year of the Blackbird’. In these years 361 respectively 535 nest records were submitted by dedicated volunteers, far more than the average of 83 per year in 1995-2020. Blackbirds started egg-laying in urban areas earlier than in woodland habitat (Fig. 2), and seem to have advanced egg-laying by a week since 1990. On average 3.4 young fledged per successful nest, without clear differences between habitats or time periods. On average 26.1% of Blackbird nests were successful. Nest success was higher in urban areas than in woodlands, but also declined stronger over time (Fig. 3). Within urban areas, the number of fledged young per successful nest decreased with increasing urbanisation (Fig. 4), but not nest success. Within woodlands, nest success was lower in the northern part of the country, where population abundance decreased, as compared to other parts. Gathering data on reproduction and survival from other nationwide surveys is necessary to assess the relative importance of these demographic drivers for the recent Blackbird decline.

Read the whole publication here (in Dutch).