Shifts in spring temperatures in central Europe may be having a significant effect on the ability of birds to breed successfully, say scientists.

Climate change is changing all these populations of birds Dr Marcel Visser, Netherlands Institute of Ecology

While the full impact of climate change is not yet clear, some birds whose populations rely on hatching two clutches of eggs a year may be hit hard.

The research, covering two decades of data and published in a journal of the Royal Society, looked at populations of great tits (Parus major) and blue tits (Parus caeruleus)

However, the researchers said that these species were representative of many other common European birds.

The breeding behaviour of tits varies throughout Europe, with some populations producing just one clutch of eggs in spring and others managing two.

Food shortage

Obviously, the birds choose spring because it is the time of year with an abundance of suitable food - in this case caterpillars and suchlike.

However, a warmer spring hastens the development of the caterpillars, meaning there is a shorter period before they become butterflies or moths.

This means there may be insufficient food to support two broods in a single spring.

The researchers found that in areas in which "double-brooding" was commonplace, the move was towards single brooding.

And in areas in which birds only produced one brood, the timing of egg-laying tended to be earlier.

This, said the researchers, was clear evidence that climate change was having an impact.

Wait and see

Dr Marcel Visser, from the Netherlands Institute of Ecology, said many factors would influence whether there would be an adverse impact on bird populations over time.

However, he said it was likely that a move from "double-brooding" to single clutches would not be beneficial.

He told BBC News Online: "Climate change is changing all these populations of birds.

"Obviously, the warmer winters might mean that more of the birds are likely to survive through the winter.

"What we are trying to find out now is whether these birds are likely to adapt to the changes."

John Lanchbery, head of climate change at the RSPB, told BBC News Online that he would expect to see more opportunistic species moving into new areas further north.

However, he added: "They can only do this if the food is there for them to eat.

"The danger is if different species move at different rates - you could end up with a different ecosystem."