60 years of Fair Isle records show changes in spring migration

Willow Warbler is now arriving much later in spring than it did 60 years ago. Photo: Aviceda (commons.wikimedia.org).
Willow Warbler is now arriving much later in spring than it did 60 years ago. Photo: Aviceda (commons.wikimedia.org).
The first results of a major survey of bird migration are revealing dramatic and unexpected changes in the numbers and timing of some long-distance migrants coming from Africa.

Continuous records made by Fair Isle Bird Observatory for more than 60 years show that spring migration has got much earlier in recent years for many species, such as Swallow, which is arriving up to three weeks earlier. Perhaps more surprisingly, some species such as Willow Warbler are migrating much later in spring.

In addition, considerable changes are apparent not just in the timing of spring bird migration but also later in the year. For example, autumn migration of House Martins has got progressively later, again by up to three weeks compared to 60 years ago.

Dr Will Miles of the Fair Isle Migration Project presents some of his initial findings at RSPB Scotland’s Big Nature Festival, Musselburgh, on Saturday 23 May. The Migration Project is a scientific collaboration between the Fair Isle Bird Observatory Trust and the University of Aberdeen.

Dr Miles said: “The natural world is changing, including the timing and numbers of birds on migration, and a crucial challenge facing scientists is to identify and understand these changes and their causes. It’s too early to say for sure why some birds are arriving so much earlier on Fair Isle while others seem to be delaying their arrival, but possible causes include changing climate and weather patterns, [as well as] changes in the summer breeding range and population size of many species across Europe.”

Fair Isle is Britain’s most remote inhabited island, and lies between Shetland and Orkney and is an internationally renowned hot-spot for bird migration. For more than 60 years the Fair Isle Bird Observatory has made daily census counts of migrant birds, while incidentally the island has recorded more first sightings of rare birds than any other place in Britain. The obervatory's written record was recently digitised, producing an extremely detailed and valuable dataset. The Fair Isle Migration Project is a brand new initiative to analyse this dataset and uncover its secrets.

As well as changes in migration patterns it is revealing that the number of scarce migrant birds arriving in Scotland from Eastern Europe and Siberia in the autumn has risen sharply over the last 60 years, and is continuing to do so. Birds such as Yellow-browed and Barred Warblers have increased in number.
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