Researchers examining three decades’ worth of data from the Hanko Bird Observatory in Finland have discovered that some bird species are delaying migration by up to a month.
Volunteers at the Hanko Bird Observatory have been carrying out daily counts of the visiting birds since 1979. This 30-year data set has allowed researchers to create a ‘migration census’, detailing which species have been migrating south from Finland and when they have been leaving.
Of the 15 species counted at the Finnish observatory, 6 were found to be setting off on their migration significantly later than they did 30 years ago. These include species such as the greylag goose, the goldeneye and the teal. The tufted duck showed the most marked delay in migration, leaving more than a month later than in previous years.
Climate change indicators
The study shows that waterfowl are responding rapidly to climate change and could be used as indicators of warming in the future. Lead author of the study, Dr Lehikoinen, explained, “One thing that’s been found in other studies as well as ours is the temperature of the water has been increasing even more rapidly than the air temperature. This means there’s more food available for these species [further north].”
As well as delaying their migration, some birds are also wintering further north as temperatures increase. As a result, many species are no longer making the journey to the UK during winter, which is often the last stop on the migration route, and the number of species overwintering in this country has dropped. At the Wildfowl and Wetlands Trust (WWT) Slimbridge reserve there has been a 75% decline in the number of overwintering white-fronted geese.
Fears for wetlands
With much lower numbers of migrating birds visiting some wetlands, there are fears that this could have a knock-on effect for the ecosystem. Dr Hilton of the WWT explains, “These are quite big changes ecologically. If you suddenly lose thousands of geese from a wetland, there are bound to be big effects on that wetland.”
It is hoped that future studies by the scientists in Finland will identify the species of bird whose range has shifted northwards, and also those that have declined globally.
Read the full report by the BBC – Autumn’s birds delay migration.
Find out more about the original study in the Journal of Ornithology – Delayed autumn migration in northern European waterfowl.
Find out more about climate change and the species that it affects in ARKive’s climate change pages.
Becky Moran, ARKive Species Text Author