Songbird toll linked to exotic shrubs

A recent study suggests that non-native habitat impacts songbirds such as the American robin.

December 27, 1999
Web posted at: 2:40 p.m. EST (1940 GMT)

By Margot Higgins

The decline of songbirds may be related to the proliferation of non-native shrubs, a recent study suggests. Birds that nest in non-native plants, most of which lack the height or physical deterrents of native plants, may sacrifice more eggs to predators such as raccoons and possums, the report notes.

"Here is an ecological trap if there ever was one," said Chris Whelan, a researcher at the Illinois Natural History Survey who conducted the study.

Introduced from Europe and Asia mostly for their aesthetic qualities, non-native shrubs are prevalent throughout the United States. Exotic honeysuckle and buckhorn sometimes dominate the lower levels of forests, particularly small, fragmented preserves surrounded by urban sprawl.

For six years Whelan studied nest predation of American robins and wood thrushes in a 500-acre deciduous woodland preserve near Chicago. There, non-native shrubs have largely replaced traditional nesting shrubs, including arrowwood and hawthorne.

"Our study focused on what makes predators click," said Whelan. Thinking like a predator, Whelan discovered that non-native shrubs generally aren't as high as their native counterparts. He also found that exotic shrubs have heavier branches with less physical deterrents such as thorns. "These factors are good for nest-building, but also provide a good physical structure for predators to move around in," Whelan said.

Scientists have blamed nest predation for recent declines in wood thrush populations. During the study, researchers found that the number of robins nesting in non-native honeysuckle has increased six-fold, from five percent to more than 30 percent. They believe honeysuckle offers an attractive nesting site because it often blooms before native shrubs do.

Whelan plans to research the extent of this predation trend by examining other locations throughout the United States. His study is published in the December Issue of Conservation Biology.

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