Study says road noise, development may lead to nesting failure

The American kestrel is a small, cavity-nesting falcon seen frequently in rural and semi-urban areas in the Grand Valley and elsewhere. A study indicates the bird shows high vulnerability to road noise and intrusions from development.

A new study indicates bird species considered “tolerant” of human activity may be adversely impacted by human disturbance to a far greater degree than previously believed.

The study, authored by Erin H. Strasser and Julie A. Heath of Boise State University, was published in the British Ecological Society’s Journal of Applied Ecology.

A key finding of the study was American kestrels nesting close to roads and developed areas had elevated stress hormones and high rates of nest abandonment, about 10 times higher than kestrels in less-developed areas.

American kestrels are small, colorful falcons often seen perched along roadways, and they are abundant in urban and agricultural areas.

“In the case of the kestrel, the bird is possibly drawn into the urban environment by the abundant nesting and perching opportunities that environment provides and by the improved prey visibility provided by shorter grass,” Heath said. “Unfortunately, this dynamic creates an ecological trap as ultimately the stresses caused by human activity lead the bird to abandon nests far more frequently.”

The study involved the monitoring of 89 nest boxes (28 nests) along Idaho’s Interstate 84 as well as on posts and trees along secondary roads in other areas in the breeding seasons of 2008 and 2009.

Most (23 nests, 88 percent) of the nests that failed did so during incubation. Only three nests failed during the nestling stage. Sixteen of the 26 failed nests (62 percent) were abandoned.

The study says cavity-nesting birds, such as kestrels inhabiting noisy environments, may compensate for decreased auditory cues by increasing vigilance behavior, such as visual scans from the nest entrance or flushing from the nest.

This leads to changes in energy allocation or extended periods away from the nest during incubation.

This behavior appears to be followed, at a high rate, by nest abandonment.

“Birds evolved in an environment that was not dominated by humans,” Heath said. “In recent history, human roads and structures have left few areas untouched. We’re just starting to understand the real consequences.”

Given that the vast majority of land in the continental United States is within a mile of a road, wildlife increasingly are exposed to chronic levels of road noise.

The resulting increase in stress levels could cause fundamental changes in physiology and behavior across species inhabiting human-dominated environments, which over time could lead to population declines.


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