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Climate change effects on migratory birds and on the ecology and behaviour of the willow warbler (Phylloscopus trochilus)
Stockholm University, Faculty of Science, Department of Zoology.
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 [en]
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: urn:nbn:se:su:diva-120409ISBN: 978-91-7649-256-7 (print)OAI: oai:DiVA.org:su-120409DiVA: diva2:852581
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
List of papers
1. Long-term phenological shifts and intra-specific differences in migratory change in the willow warbler Phylloscopus trochilus
Open this publication in new window or tab >>Long-term phenological shifts and intra-specific differences in migratory change in the willow warbler Phylloscopus trochilus
2015 (English)In: Journal of Avian Biology, ISSN 0908-8857, E-ISSN 1600-048X, Vol. 46, no 1, 97-106 p.Article in journal (Refereed) Published
Abstract [en]

Climate change can influence many aspects of avian phenology and especially migratory shifts and changes in breeding onset receive much research interest in this context. However, changes in these different life-cycle events in birds are often investigated separately and by means of ringing records of mixed populations. In this long-term study on the willow warbler Phylloscopus trochilus, we investigated timing of spring and autumn migration in conjunction with timing of breeding. We made distinction among individuals with regard to age, sex, juvenile origin and migratory phase. The data set comprised 22-yr of ringing records and two temporally separated data sets of egg-laying dates and arrival of the breeding population close to the ringing site. The results reveal an overall advancement consistent in most, but not all, phenological events. During spring migration, early and median passage of males and females became earlier by between 4.4 to 6.3 d and median egg-laying dates became earlier by 5 d. Male arrival advanced more, which may lead to an increase in the degree of protandry in the future. Among breeding individuals, only female arrival advanced in timing. In autumn, adults and locally hatched juvenile females did not advanced median passage, but locally hatched juvenile males appeared 4.2 d earlier. Migrating juvenile males and females advanced passage both in early and median migratory phase by between 8.4 to 10.1 d. The dissimilarities in the response between birds of different age, sex and migratory phase emphasize that environmental change may elicit intra-specific selection pressures. The overall consistency of the phenological change in spring, autumn and egg-laying, coupled with the unchanged number of days between median spring and autumn migration in adults, indicate that the breeding area residence has advanced seasonally but remained temporally constant.

National Category
Zoology
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-115364 (URN)10.1111/jav.00484 (DOI)000349082800012 ()
Note

AuthorCount:4;

Available from: 2015-03-20 Created: 2015-03-20 Last updated: 2017-12-04Bibliographically approved
2. Regional differences in phenological response to climate change in willow warblers (Phylloscopus trochilus)
Open this publication in new window or tab >>Regional differences in phenological response to climate change in willow warblers (Phylloscopus trochilus)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Phenological responses to climate change are known to differ between bird species, and even differences within species are known to occur, but are rarely considered. With data sets comprising 22 years of bird ringing records (1990-2012) and focusing on differences between populations, sexes and individuals in different migratory phases, we investigated migratory change in willow warblers (Phylloscopus trochilus spp.) at one northern and one southern site in Sweden. In order to investigate effects of climate on changes in arrival and departure dates, three climatic variables were included in the analysis (local temperature, regional growing season onset, GSO, and the North Atlantic Oscillation, NAO). At the northern site there was no change in onset of autumn migration, whereas both spring and autumn migration advanced at the southern site. Of the climate variables, only September temperatures and the GSO showed a change, and the latter advanced at both sites by 0.3-0.6days/year. Analyses revealed that a combination of GSO and the NAO, acting together with local spring temperatures, not only displayed positive relationship with early arriving individuals in spring at the southern site, but also with early departing juveniles in autumn at the southern site. These correlations indicate that spring migratory phenology may resonate through life-history events and affect phenological steps during the entire breeding area residence. As migratory changed differed between the latitudinally separate locations during autumn even though GSO showed similar advancement in both regions, we propose that local adaptation may prepare individuals differently in reacting to environmental change. Our results corroborate that phenological response to climate change is not uniform within a species and that it in fact appears to be restricted to certain individuals.

National Category
Biological Sciences
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-120532 (URN)
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-01-29Bibliographically approved
3. Point of no return – absence of returning birds in the philopatric willow warbler (Phylloscopus trochilus)
Open this publication in new window or tab >>Point of no return – absence of returning birds in the philopatric willow warbler (Phylloscopus trochilus)
(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:nbn:se:su:diva-120533 (URN)
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-01-29Bibliographically approved
4. Spatio-temporal perspectives on the effects of land use change on two common bird species: the past, present and future
Open this publication in new window or tab >>Spatio-temporal perspectives on the effects of land use change on two common bird species: the past, present and future
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Land-use change is a main driver of habitat loss and a force that can utterly alter landscapes. During the last 100 years the agricultural landscape of Northern Europe has been transformed by intensification of forestry, extensively effecting biodiversity. In this study we utilize historical maps to investigate the effect of 100 years of land use change on the availability of potential territories for the two most common bird species in Sweden, the willow warbler (Phylloscopus trochilus) and the chaffinch (Fringilla coelebs). In addition, we used the species’ habitat preferences to construct a future scenario and estimated how increased fibre and timber demands and climate change could shape territory availability further. The results suggest that the decrease in forest grazing and landscape heterogeneity that has occurred between 1900-2013 have negatively affected the willow warbler, whereas the chaffinch has benefitted by the increase in forest cover but lost living space because of the decrease in heterogeneity. In the future scenario, the climate-induced augmented turn-over rate of forest harvesting cause an increase in early succession forest, creating habitat for both species. However, this future entails an even greater loss of heterogeneity and if this negative effect is to be hindered, the most preferred habitats by the two species must be promoted. These most preferred habitats are also associated with high biodiversity. Thus, conservation of preferred habitats will promote both the two common study species and also generate benefits for biodiversity, exemplifying how common, more easily-monitored species can be utilized in conservation. Additionally, by considering past land use changes and current population status, the response by the two species to alterations in the landscape is better understood and future resilience to land use change easier anticipated.

National Category
Biological Sciences
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-120534 (URN)
Available from: 2015-09-11 Created: 2015-09-11 Last updated: 2016-01-29Bibliographically approved
5. Change in spring arrival of migratory birds under an era of climate change, Swedish data from the last 140 years
Open this publication in new window or tab >>Change in spring arrival of migratory birds under an era of climate change, Swedish data from the last 140 years
Show others...
2015 (English)In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, S69-S77 p.Article in journal (Refereed) Published
Abstract [en]

Many migratory bird species have advanced their spring arrival during the latest decades, most probably due to climate change. However, studies on migratory phenology in the period before recent global warming are scarce. We have analyzed a historical dataset (1873-1917) of spring arrival to southern and central Sweden of 14 migratory bird species. In addition, we have used relative differences between historical and present-day observations (1984-2013) to evaluate the effect of latitude and migratory strategy on day of arrival over time. There was a larger change in spring phenology in short-distance migrants than in long-distance migrants. Interestingly, the results further suggest that climate change has affected the phenology of short-distance migrants more in southern than in central Sweden. The results suggest that the much earlier calculated arrival to southern Sweden among short-distance migrants mirrors a change in location of wintering areas, hence, connecting migration phenology and wintering range shifts.

Keyword
Bird migration, Phenology, Migratory strategy, Climate changes, Spring arrival
National Category
Earth and Related Environmental Sciences Biological Sciences
Research subject
Ethology
Identifiers
urn:nbn:se:su:diva-114251 (URN)10.1007/s13280-014-0600-1 (DOI)000347680100008 ()25576282 (PubMedID)
Note

AuthorCount:7;

Available from: 2015-03-26 Created: 2015-02-25 Last updated: 2017-12-04Bibliographically approved

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