Spring Migrations Beginning Earlier
Studies into the timing of seasonal bird migrations in United Kingdom, Germany, Switzerland and Denmark have uncovered the same trend: birds are flying north earlier every year. Scientists figure that warmer spring weather due to climate change has prompted all species of songbirds studied from 1970 to 2000 in these countries to move their spring migrations ahead.
The largest advance has taken place among the first birds migrating through central and northern Europe after wintering near the Mediterranean. Individual forerunners of species such as wren, dunnock, blackbird, goldcrest and reed bunting are heading north about one week earlier every decade. For the majority of these short-distance migrants however, the gain is much less, averaging under two days a decade.
More wide-spread response has occurred among birds arriving from south of the Sahara desert, including spotted flycatcher, willow warbler and blackcap. Flocks of these long-distance fliers are travelling to northern latitudes 3.2 days sooner each decade.
Despite the advances, most birds are not spending more time at breeding grounds located in Sweden and Finland. Instead they fly south earlier in autumn. The exception is birds arriving later than most from sub-Saharan Africa. They have extended their breeding season in the north by arriving earlier and leaving around the same date each fall.
Kasper Thorup, Anders P. Tøttrup and Carsten Rahbek. 2007. Patterns of phenological changes in migratory birds. Oecologia. 151(4): 697-703.