Biologists at Boise State University say birds thought to tolerate humans, like American kestrels, may not be so laid back around us.
Erin H. Strasser and Julie A. Heath of Boise State University laid out their case in a study published in the British Ecological Society’s Journal of Applied Ecology.
American kestrels nesting near roads and development had elevated stress hormones and abandoned their nests 10 times more often than kestrels living outside of developed areas. Kestrels are small, colorful falcons often seen perched along roadways and 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 in a press release. “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 biologists monitored of 89 nest boxes along Interstate 84, which had 28 nests. Posts and trees along secondary roads also had nests during the breeding seasons of 2008 and 2009 in the following areas: suburban (10 nests), rural-residential (24 nests), agricultural (22 nests) and shrubland (15 nests). Twenty-three nests failed during incubation, and three nests failed during nesting. Sixteen of the 26 failed nests were abandoned.
Strasser and Heath say that cavity nesting birds, such as kestrels, that inhabit noisy environments may compensate for decreased auditory cues by increasing vigilance behavior leading to changes in more activity that uses energy or extended periods away from the nest during incubation. This behavior appears to be followed, at a high rate, by nest abandonment, they write.
The researchers found that that female kestrels nesting in areas with high human activity, such as along noisy roadways, have higher corticosterone levels. But male kestrels in the same areas do not have more of the stress hormone. This could be because females spend more time in the nesting boxes near the disturbance.
“Birds evolved in an environment that was not dominated by humans,” Heath said in the press release. “In recent history, human roads and structures have left few areas untouched. We’re just starting to understand the real consequences.”
The study concludes that until regulations or economic incentives are developed to encourage engineering innovations that result in quieter roads, projects in areas of human activity with favorable habitat should be discouraged in order to decrease the risk of ecological traps.
“Many people think that since they see certain species of birds in urban environments, that they must have adapted to those unnatural surroundings,” said George Fenwick, President of American Bird Conservancy. “This study certainly suggests that at least in some circumstances, the exact opposite is true. Birds are being lured away from their more natural environment, into areas where their ability to reproduce is clearly being compromised.”