Passerines in Swedish Lapland generally did not advance timing of breeding over the last 30 years

Abstract

Abstract

Birds are adapted to time their breeding so that the most demanding part of breeding (the feeding of nestlings) coincides with food availability. This means that they must be able to track yearly changes in local weather conditions. There are numerous examples of how populations in temperate regions have advanced their timing of breeding in response to a warming climate in the last decades. I investigated the timing of breeding of 14 passerines species in Swedish Lapland over a period of 30 years, including several open-nesting species and both long- and short-distance migrants. Hatching date was estimated from the progress of post-juvenile moult of young birds mist-netted in the period around independence from the parents. Of the 14 species, 12 did not advance their hatching times significantly. The between-year variation in hatching times was almost exclusively related to local May temperatures and no relation to precipitation or winter climate (NAO index) was found. Whereas temperature in April, July and August, increased significantly with 2.2°C, 1.6°C, 1.8°C and respectively, temperatures in May did not change. This is most likely the reason why there were no pronounced advancements of hatching dates in most of the species. In the same period, spring arrival in southern Sweden, an area the Ammarnäs birds pass during migration, has advanced due to warmer climate. Although birds might be able to advance their spring migration due to better conditions en route, their timing of breeding may be limited by the climate at the breeding area. Possibly advancement of breeding is limited by food availability that is not affected by the current state of climate change in this area. If in the future climate change will be more pronounced in May, this might have considerable effects on these populations.

Abstract

Popular science summary:

Climate change, and its effect on nature, is presently a hot research topic. Many studies have focused on the effect of recent climate change on breeding and spring migration in birds. Several bird populations have been shown to advance migration or breeding. It has been suggested that if they do not do this they might miss optimal breeding conditions such as peak food availability when raising young. My study looked at the timing of breeding of 14 species of small songbirds in Swedish Lapland, at a site just south of the Polar Circle where climate change has not been evident until the last decade.

During 30 years (1983–2012) birds were trapped in a standardized way each summer, near Lake Tjulträsk in Ammarnäs, Sweden. In my analysis I included the 14 most commonly trapped species; Bluethroat, Willow Warbler, Spotted Flycatcher, Pied Flycatcher, Yellow Wagtail, Tree Pipit, Common Redstart, Brambling, Common Redpoll, Eurasian Siskin, Redwing, Reed Bunting, White Wagtail and Meadow Pipit. The first seven of these species are long-distance migrants to sub-Saharan Africa or Asia. The others are short- to medium-distance migrants, spending the winter within Europe. Pied Flycatcher and Redstart are hole-nesting species, while the other 12 species are open-nesting. In late summer, juveniles of all these species undergo a partial post-juvenile moult, in which they replace all body feathers and a varying number of wing coverts. Juveniles trapped were scored based on the progress of their post-juvenile moult. Using these scores, I estimated the birds’ age in days, and thereby their hatching dates. By estimating their hatching dates I could look at trends in timing of breeding over 30 years for each species. These estimates of timing of breeding I then compared to climate data including temperature, precipitation and the North Atlantic Oscillation (NAO) winter index as an indicator for climate that the birds encounter during winter.
Out of 14 bird species, only 2 advanced their breeding significantly over the last 30 years: Siskins and Redpolls advanced their hatching dates with 13 and 7 days, respectively. Local climate did not change dramatically in the last 30 years. Precipitation varied between years but there were no trends. April, July and August temperatures have increased with 2,2°C 1,6°C and 1,8°C respectively, whereas May and June temperatures show no trends. The between-year variation in estimated hatching shows a strong relation to May temperature. Hatching dates correlated significantly to May temperatures in 12 of the 14 species. In all species but Siskin, hatching dates were most strongly correlated to May temperature. Siskin had its strongest correlation with April temperatures and three of the long-distance migrants were also significantly correlated to June temperatures. Hatching dates were not related to precipitation or the NAO index. While hatching dates related to temperatures in all species, this relation was stronger in long-distance migrants than short/medium-distance migrants. The lack of change in May temperatures could explain why there are no pronounced advancements of hatching dates in most of the analyzed species. In contrast, April temperatures in Ammarnäs have increased with 2.2°C in the last three decades but this increase does not seem to affect the timing of breeding. Several of the species do advance their spring migration in southern Sweden, but maybe upon arrival in the breeding area they have to wait for more favorable conditions. If also May temperatures will start to increase in Southern Lapland this is likely to have considerable effects on the breeding of these species.

Supervisor: Åke Lindström
Master´s Degree Project 30 credits in Animal Ecology 2013/2014
Department of Biology, Lund University.

• author: Ram, Dafne
• supervisor: Åke Lindström
• organization: Degree Projects in Biology
• course: BIOM32 20131
• year: 2014
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 4333580
• date added to LUP: 2014-02-28 16:34:50
• date last changed: 2014-02-28 16:34:50