A small long-distance migrating bird called the pied flycatcher (Ficedula hypoleuca) spends the northern hemisphere winter in West Africa, returning to northern Europe in the spring to breed.

Dutch researchers have been following the species for decades, using nestboxes in forests, observations of their arrival and departure and monitoring availability of their staple food, which is caterpillars.

They have found that the earlier arrival of warm weather causes the caterpillars to emerge sooner -- and as a result, the flycatchers may arrive too late to properly feed their young. The birds breed, but without having an adequate food supply for the nestlings.

The team, lead by Christian Both of Groningen University, looked at population numbers and caterpillar availability from 1987 to 2003.

An early food peak caused flycatcher numbers to decline by a stunning 90 percent. But when the caterpillars peaked later, the decline was only 10 percent.

"Mistiming as a result of climate change is probably a widespread phenomenon," says Both. "(The) evidence (is) that it can lead to population declines."

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