Washington, Oct 18 (IANS): Driven by a warming climate, birds typically found in more southerly regions are gradually pushing north, restructuring the communities of birds that spend their winter in northern latitudes, research has found.

Over the past two decades, the resident communities of birds that attend eastern North America's backyard bird feeders in winter have quietly been remade, the findings showed.

The readily familiar species include cardinals, chipping sparrows and Carolina wrens.

"Fifty years ago, cardinals were rare in the north-eastern United States. Carolina wrens even more so," explained study co-author Benjamin Zuckerberg from the University of Wisconsin-Madison in the US.

These birds and other warm-adapted species have greatly expanded their wintering range in a warmer world, a change that may have untold consequences for North American ecosystems, the authors noted.

The researchers measured the changes over time, resulting in the abundance of 38 bird species at feeders in eastern North America.

They specifically looked at the influence of changes in winter minimum temperature over a 22-year period on the flocks of birds that gather at backyard feeding stations.

"We conclude that a shifting winter climate has provided an opportunity for smaller, southerly distributed species to colonise new regions and promote the formation of unique winter bird assemblages throughout eastern North America," the authors wrote.

Climate models predict even warmer temperatures occurring over the next 100 years, with seasonal climate effects being the most pronounced in northern regions of the world.

The study appeared in the journal Global Change Biology.