Birds 'off the pace' with warming
French birds are moving northwards in response to climate change, but not fast enough, scientists have found.
Their data came from a large survey in which volunteer ornithologists counted more than 105 species of bird.
In the Royal Society journal Proceedings B, researchers say that the birds are lagging some 182km behind the increases in temperature.
This lag may be of particular concern to rare birds or species that have very specific food requirements.
"The flora and fauna around us are shifting over time due to climate change," said Vincent Devictor, who led the research project from the National Museum of Natural History (MNHN) in Paris.
"The result is desynchronisation. If birds and the insects on which they depend do not react in the same way, we are headed for an upheaval in the interaction between species," he told the AFP news agency.
At its worst, this desynchronisation could result in species extinctions, he said.
In 1989, French ornithologists began a systematic survey of breeding birds. Sightings are taken at set times of the year in set locations, and follow a standard protocol.
A wide variety of habitats are surveyed across the whole country, including farmland, forests, suburbs and cities.
The result is a dataset that covers virtually all wild bird species in the country, and can be used to track changes over the period.
Chaffinches are among the birds found to be nesting earlier in the UK
On average, bird populations moved 91km northward between 1989 and 2006.
In order to have kept themselves at a constant temperature as the country warmed, they would have had to move 273km northwards, the researchers calculated.
Ben Sheldon from Oxford University, who also studies nature's response to rising temperatures, commented: "At any one site, the community of birds you find there has changed over time.
"Now, more of the species that are found in warmer climates are occurring, but that change is not occurring as fast as the change in temperature is," he told BBC News.
This study did not examine whether the failure to "keep up" with rising temperatures was affecting the birds.
Evidence from other studies suggests it depends on the species involved, their habitat, how their prey are responding to climate change, and what other threats and constraints they face.
A recent study of great tits in England found they were coping well with rising temperatures, changing their egg-laying times in order to adapt to the earlier emergence of insect prey.
But in the Netherlands, the same species is suffering.
"Some species have changed their range hugely over the past two decades," observed Professor Sheldon.
"For example, the buzzard - one of our biggest birds of prey - 20 years ago was restricted to the west of Britain, but has now spread as far east as London."
Another recent study found a number of species in the UK, including the chaffinch, were laying eggs earlier than 40 years ago.
The French team suggests more research on the issue is vital if better conservation options are to be developed.