Authors: NILSSON, ANNA L. K.¹; LINDSTRÖM, ÅKE¹; JONZÉN, NICLAS²; NILSSON, SVEN G.¹; KARLSSON, LENNART³

Source: Global Change Biology, Volume 12, Number 10, October 2006 , pp. 2014-2022(9)

Publisher: Wiley-Blackwell

Abstract:

Climate change has proven to affect various aspects of the migration of birds. In response to milder winters making the habitat more profitable and increasing the survival of residents, the migratory fraction of partially migratory populations has been predicted to decline. We studied the blue tit Parus caeruleus, a common partial migrant in southern Sweden. The numbers migrating at Falsterbo, a migratory passage site in SW Sweden, has increased during the last decades, in parallel with increasing winter and annual temperatures. Migration data from Falsterbo were compared with yearly indices of the size of the breeding population as estimated by the Swedish National Bird Monitoring Programme. Over the study period 1975-2004, also the breeding population has increased in size. The proportion of blue tits migrating each year did not change over the study period, or possibly even increased slightly, which is in contrast to how climate change has been predicted to influence populations containing both migratory and resident individuals. The most important factors determining the intensity of blue tit migration in a given year was the size of an important winter food source, the beech mast crop (more migrants at lower crops) and the size of the breeding population (more migrants at higher densities).

Keywords: beech mast; breeding population size; habitat quality; Parus caeruleus; temperature; winter food

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2486.2006.01237.x

Affiliations: 1: Department of Animal Ecology, Lund University, Ecology Building, S-22362 Lund, Sweden, 2: Department of Theoretical Ecology, Lund University, Ecology Building, S-22362 Lund, Sweden, 3: Falsterbo Bird Observatory, Fyren, S-23940 Falsterbo, Sweden

Publication date: 2006-10-01

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