Parus caeruleus
Image: DONALD W. THOMAS

Global warming may have yet another negative side effect: it could disrupt birds' breeding patterns and subsequently reduce their numbers considerably, according to a new study published in today's Science.

The rise in global temperature is likely to change the normal turn of seasons such that spring will arrive earlier. Although this may seem appealing at first, an earlier spring might come without the familiar chirping of birds. Indeed, the warmer weather could lead some birds to breed earlier in the year when food is not as readily available. Fewer birds would breed and fewer would survive.

To test this hypothesis, a team of scientists from Canada, France and the U.K. took a closer look at two populations of tiny blue tits called Parus caeruleus (see image) in southern France and on the island of Corsica. They discovered that whereas the birds on Corsica bred at the time when caterpillarsa ready food sourcewere most plentiful, the birds on the mainland were out of sync. They bred several weeks before the caterpillar population reached its peak. This relative food shortage made it more difficult for the mainland blue tits to rear their young and thus reduced the number of breeding adults overall.