Global warming could have a disastrous effect on birds that migrate large distances to and from Europe, say researchers.
Short-haul migrant: The starling
However, some "short-haul" species could benefit substantially, they add.
Experts from the Swiss Ornithological Institute attempted to unravel the complex patterns of bird migration across the Alps.
Over the past two decades, scientists have noticed increases in spring temperatures in temperate areas of Europe.
They wanted to try to work out whether small changes in temperature could be a significant factor in their migratory behaviour - and perhaps even a threat to certain species as a result.
To do this, they examined records of bird caught in "mist nets" strung across one of Europe's migratory "superhighways": the Col de Bretelet in Switzerland.
Global warming could be a serious threat to some long-distance migrants and one reason for the decline of such species in Europe
Dr Lukas Jenni, Swiss Ornithological Institute
Hundreds of thousands of migrants use this pass to avoid climbing over the highest Alpine ridges.
More than 350,000 birds of 64 species have been captured, examined, and then released from the nets in this location between 1958 and 1999.
Dr Lukas Jenni and Dr Marc Kery from the institute found that while there were no uniform shifts in the timing of autumn migration, a more complex pattern emerged.
They believe this shows that some species could be losing out because of climate change, while others might actually benefit.
Long-distance migrants - such as those which winter south of the Sahara - are leaving earlier in the year.
Dr Jenni said: "For instance, the pied flycatcher, willow warbler and garden warbler now fly south almost a week earlier."
He suggested that some of these birds might be caught out by a narrowing window of opportunity to cross the Sahara.
"The migration could be constrained by the onset of the dry season in the Sahel region. This region suffers serious drought conditions.
"Migrant species would want to cross the region before the drought had started.
"The spring arrival of these species and the start of their breeding season is also constrained - so they are losing out to species with shorter migration patterns."
He added: "Global warming could be a serious threat to some long-distance migrants and one reason for the decline of such species in Europe."
Short-haul migrational birds could benefit, he said, from a longer breeding season, and perhaps the need to migrate shorter distances in future.
The research was published in the Royal Society journal Proceedings B.