Warmer Climate Sends Birds North

Some birds nesting in the central and eastern United States have moved their range over a hundred miles farther north in less than three decades.

Scientists at University of Louisiana attribute the northward movement of breeding birds to climatic warming.

Among the 26 birds they studied, nine species significantly shifted between 1971 and 1998 the northern limit of where they raise young. Overall, the average shift in range totalled 2.35 kilometres (1.46 miles) a year northwards. The birds that researchers investigated were warblers, flycatchers, sparrows, chickadees and others that eat insects or seeds and live around trees.

Some birds were especially big movers during the 26 years. By the end of the century, great-tailed grackles nested about 335 kilometres (208 miles) farther north than observed prior to 1972. Blue-gray gnatcatchers moved about 315 km northwards, Inca doves 255 km and Kentucky warblers 150 km.

At the same time, only two species significantly contracted the northern boundary of their range. The northern limit of where Bachman's sparrows nest retreated about 175 km (109 miles) and Bewick's wrens 110 km southwards. These birds could be affected by disappearing habitat or declining populations.

The North American results parallel those obtained in Great Britain over a similar time period. There, a northward shift averaging one kilometre a year was observed in breeding birds. Finding the same trend on two continents leads this study's authors to conclude that the warming climate is the most plausible cause of birds settling farther north.