VCU biologist credits global warming for birds' early arrival

By Mike Frontiero
VCU School of Education

RICHMOND, Va. – The first eggs are hatching along a swampy area of Virginia’s James River that serves as the summer home for thousands of Prothonotary Warblers. It’s a little early to see these baby warblers in their nesting boxes. But, then again, their parents arrived in April from their winter nesting area in the Caribbean and South America a full three days earlier than expected this year and started laying eggs early.

This early arrival of the Prothonotary Warblers in Central Virginia is part of a trend that biologist and ecologist Charles R. Blem, Ph.D., and his team at Virginia Commonwealth University have been tracking for the past 16 years. During this time, they’ve noticed that the warblers have returned from their tropical vacation an average of one day earlier each year. They’ve also seen a change in the number of eggs produced and incubated at one time.

Blem thinks the reason is global warming. The warmer it gets, the sooner the birds return and get busy raising their families.

"There are many factors that could be causing the birds to come back earlier, but the most obvious and logical one is global warming," Blem said.

Blem says temperatures at the nesting site on the James River in Henrico County have risen one degree since 1986. If temperatures continue to rise, he believes the Prothonotary Warbler and other birds will eventually forgo winter migration and become resident species of North America.

"Every year we get a new record of birds over-wintering, which didn't happen before. That's going to change the dynamic here, I think," Blem said.

Using bands that he and other bird experts attach to the birds' legs, Blem has been able to track the warblers' migratory patterns and breeding habits. "We can tell you if this bird was banded as a young bird, or as an adult bird, and very often how old they are. We've caught some that were banded as long as eight years ago; that's actually very unusual," Blem said.

The Prothonatory Warbler, also known as the Golden Swamp Warbler, is a striking bright orange-yellow color and measures about five inches long. It flies only at night during migration and breeds throughout the southeastern United States and in southern Canada.

The bird is expected to remain at its summer nesting site through early August.