Declining Songbird Population Linked to Exotic Shrubs
12/26/99
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Title: Songbird toll linked to exotic shrubs
Source: Environmental News Network
Status: Copyright 1999, contact source for permission to reprint
Date: December 26, 1999
Byline: 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.