The survival of the fittest rings true for every member of the animal kingdom: as the environment changes from time to time, only the well-suited could survive.

But if man-made climate change is added to the picture, what could possibly happen?

For bird species in the United States and in European countries, the "winning" species outperform and outlast the "losing" ones, a new study revealed.

Advantaged and Disadvantaged

Led by conservation biologist Stephen Willis, a team of researchers examined how the occurrence of some 380 American bird species and some 145 European bird species were affected by climate change between 1980 and 2010.

Willis, who is part of University of Durham's School of Biological and Biomedical Sciences, said the study allowed them to decide whether each of the species had been advantaged or disadvantaged by climate change. To do so, the team used annual bird census data from every European country and U.S. state.

Although species in the U.S. and in European countries responded differently to climate change, the degree to which the advantaged species outperform least advantaged ones was similar.

"Climate seems to be having a consistent effect," said Willis.

Species That Thrive and Survive

According to the study, some of the most advantaged species in the U.S. include the Anhinga, the orchard oriole, and Cassin's kingbird. The more disadvantaged species include the common grackle, the Canada warbler, and the white-throated sparrow.

In Europe, the most advantaged species are Cetti's warbler, the bee-eater, and the chiffchaff, while the willow fit and brambling fare poorly.

Many bird species are thriving in some areas, while simultaneously declining in others, researchers said. For instance, the American robin is on the rise in North and South Dakota, but it is beginning to become scarcer in Louisiana and Mississippi.

In Europe, the Dartford warbler has become eight times more abundant in the United Kingdom since the 1980s, but it is now declining in Spain.

Climate Change Indicator

Willis said the pattern of winners versus losers hides several important differences. In Europe, the disadvantaged species have declined significantly, while those that are supposedly advantaged remain more or less static.

In the U.S, the relatively disadvantaged bird species have maintained stable population sizes, while the advantaged ones have grown in population.

Willis and his colleagues find the trend interesting, but they have yet to find out why this is the case.

Meanwhile, Philip Stephens, a co-author of the study, said that if climate change had no impact, the average population trend of species in the two groups would be equal.

"But the differences expose the fact that recent climate change has already favored one set of species over another," added Stephens.

The team's findings, published in the journal Science, indicate a new climate impact indicator for biodiversity. Willis believes the same approach could be applied to bees, butterflies and dragonflies, all of which are highly-susceptible to climate change.

Photo: Greg Schechter | Flickr