Latitudinal differences in long-term migratory change in the willow warbler (Phylloscopus trochilus)

Johanna Hedlund, Sven Jakobsson, Cecilia Kullberg, Thord Fransson

Forskningsoutput: KonferensbidragKonferensabstractPeer review


Location is everything and the geographical distribution of populations will make them differentially affected by global warming. Sweden’s north to south orientation presents a great frame for studying the effect of latitudinal climate change. We present a long-term study on the migratory behaviour of two populations of Willow Warbler subspecies (southern Phylloscopus trochilus trochilus and northern P.t. acredula). The material covers a 31-year period and is analysed in relation to climatic indices. Three study sites are considered, the island of Gotland in southern Sweden (ringing recoveries 1990-2012, breeding data 1992-93, 2011-13) and in northern Sweden Abisko (breeding data 2011-13) and Haparanda (autumn ringing recoveries 1982-2012).We found that the both the spring passage over Gotland and the arrival of breeding birds to the island have advanced significantly by 0.38 days/year. Egg-laying dates have also advanced and are now 5days earlier than in the 1990s. The degree of protandry on Gotland has increased between 1990-2012 but not significantly. In the north, median spring arrival dates of males and females at Abisko are 26 resp. 24 days later than on Gotland. Sex differences in arrival is however similar and protandry is as pronounced in Abisko as on Gotland. During autumn the median passage date of juveniles in the north has remained unchanged, almost delayed, but has advanced by 8,8 days on Gotland. This can be compared to another study in northern Norway, where spring arrival of northern acredula had been delayed. In conclusion, trochilus have advanced the breeding period but not prolonged it, whereas acredula seem have delayed the breeding period. Neither local temperatures nor the North Atlantic Oscillation index could explain any of the migratory shifts. However, the start of the growing season in southern Sweden has advanced and could explain the advancement of male spring passage over Gotland.
StatusPublished - 2014
Externt publiceradJa
EvenemangThe 26th International Congress of Ornithology - Tokyo, Japan
Varaktighet: 2014 aug. 22 → …


KonferensThe 26th International Congress of Ornithology
Period2014/08/22 → …


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