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Point of no return – absence of returning birds in the philopatric willow warbler (Phylloscopus trochilus)
Stockholm University, Faculty of Science, Department of Zoology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The return of individual birds to a specific area in successional years, i.e. philopatry, is a remarkable behavioural trait. Here we report on the remarkably reversed: the complete absence of returning individuals of a migratory passerine with otherwise pronounced philopatry. At a high latitude study site in Abisko in northern Sweden none of the banded adult willow warblers (Phylloscopus trochilus) returned to breed 2011-14. This is in stark contrast to our southern study sites, where 15-38% of adults return and also to all other reports in the literature. We investigated three parameters known to influence philopatry; nest predation, breeding success and breeding density, and predicted that absence of philopatry should co-occur with low breeding success, low breeding density or high nest predation. The results did not corroborate this, except that breeding density was lower at Abisko (64 pairs/km2) than at the southern sites (144-106 pairs/km2, 101 pairs/km2). Instead, we suggest that the absence of philopatry is caused by an influx of individuals of a nomadic breeding strategy and that this range expansion is enabled by milder climate and increased availability of habitats in the north.

National Category
Biological Sciences
Research subject
Ethology
Identifiers
URN: urn:nbn:se:su:diva-120533OAI: oai:DiVA.org:su-120533DiVA: diva2:853172
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-01-29Bibliographically approved
In thesis
1. Climate change effects on migratory birds and on the ecology and behaviour of the willow warbler (Phylloscopus trochilus)
Open this publication in new window or tab >>Climate change effects on migratory birds and on the ecology and behaviour of the willow warbler (Phylloscopus trochilus)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recent global climate change is influencing the behaviour and ecology of species worldwide. Birds are typical systems to study in this context, as they are often migratory and thus subjected to a variety of environmental effects. This thesis employs the use of long-term ringing records, field observations, historical maps and historical volunteer observations with the aim of describing behavioural and ecological responses of birds to the current environmental change. An investigation into the spring arrival, reproduction and autumn departure in willow warblers (Phylloscopus trochilus) breeding at a southern study site in Sweden (65°N 18°E) showed that all three phenological events had advanced in parallel. Thus birds arrive earlier, start breeding earlier and leave Sweden earlier, with the breeding period staying the same in length. By teasing apart the migratory responses of different individuals, it became clear that particularly early arriving males and early departing juveniles had advanced migration. However, willow warblers migrating past a northern study site in Sweden (65°N 23°E) displayed no change in autumn departure. When migration in the two regionally separate populations were analyzed in relation to climatic variables, the results indicated that foremost a combined effect of growing season onset and the North Atlantic Oscillation influenced migratory timing, and only in individuals that had advanced migration. As growing season onset had advanced at both regions, but only elicited migratory change in southern willow warblers, it is proposed that intra-specific difference between populations prepare them differently to climate change. Willow warblers breeding at northern latitudes were also displaying absence of an otherwise common behaviour of the species: philopatry. It is suggested that the climate induced change in onset of the growing season, coupled with an increase in available territories, could have enabled a southern influx of dispersal-prone birds adopting a less philopatric breeding behaviour. Availability of territories was also studied in southern Sweden, in relation to 100 years of land use change and future climate change effects on forestry. The mass-conversion of grazed forest into coniferous sylvicultures that has occurred in Sweden 1900-2013 was shown to have negatively affected territory availability for willow warblers. The second most common bird species in Sweden, the chaffinch (Fringilla coelebs), was however shown to be largely unaffected. In a future scenario where rising temperatures will increase growth rates of trees, harvest rotation will be faster and both sylvicultures and logged areas will increase in coverage, favouring both species. Thus commonness in terms of landscape and species occurrence has altered historically and is dynamically linked. Historic perspectives were also applied to observations of spring arrival of 14 migratory bird species. A relative comparison of two data sets, collected over 140 years, revealed that short-distance migrants have changed their spring arrival more than long-distance migrants in southern Sweden. In conclusion, the results of this thesis provide insights into climate change effects on avian behaviour and ecology, document unique observations and contribute with a great spectrum of knowledge, from exact details on responses by individual birds, through long-term changes in populations to historical perspectives on shifts in entire landscapes

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2015. 121 p.
Keyword
climate change, bird migration, ecology, phenology, bird, avian, willow warbler, chaffinch, land use change, landscape ecology, historical ecology
National Category
Zoology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-120409 (URN)978-91-7649-256-7 (ISBN)
Public defence
2015-10-23, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2015-10-01 Created: 2015-09-09 Last updated: 2016-01-29Bibliographically approved

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