May 10, 2013 — American kestrels, small colorful falcons often seen perched along roadways, are abundant in urban and agricultural areas. Shorter grass makes insects, snakes, mice and other prey more visible, and signposts, fences and telephone poles provide excellent perches. However a new study from scientists at Boise State University in Idaho shows that even species considered "tolerant" of human activity may be adversely impacted by human disturbance; Kestrels nesting in close proximity to roads and developed areas had elevated stress hormones and high rates of nest abandonment. The apparently favorable location, then, becomes an ecological trap.
The peer-reviewed paper "Reproductive failure of a human-tolerant species, the American kestrel, is associated with stress and human disturbance," was published in the British Ecological Society's Journal of Applied Ecology(May 10, 2013). Boise State University graduate student Erin Strasser, now with the Rocky Mountain Bird Observatory, and Julie Heath, a professor in the Boise State Department of Biological Sciences and Raptor Research Center, conducted the research.
Strasser and Heath conducted research along one of Idaho's major expressways, Interstate 84, and in suburban and rural areas south of the state's capital city of Boise. Since 1987, researchers from Boise State and the U.S. Geological Survey have monitored a number of nest boxes located along the area's roadways, in people's back yards, and in sagebrush-steppe habitat.
In this study, Strasser and Heath were interested in understanding how human-dominated landscapes affect breeding kestrels, with particular attention paid to the link between disturbance, stress and nest failure. The two monitored the boxes to determine nest fate, and collected a small blood sample from adult birds. The researchers were looking at corticosterone levels, which indicate stress levels (the equivalent in humans is cortisol). Corticosterone can lead to behavioral and physiological changes that allow individuals to cope with stressful situations, while suppressing other activities such as reproduction.