Effects of anthropogenic disturbance on avian distribution, reproduction, and physiology.

Abstract

As human population and concomitant development increase, human-caused disturbances play an ever larger role in the fitness of wildlife. An increasing number of studies have implicated anthropogenic disturbance in having harmful effects on birds and other wildlife. Most studies, however, concentrate solely on behavioral changes, including fleeing, change in feeding habits, and shifts in habitat use. Few studies have investigated physiological changes or show a clear link between disturbances and reproductive success. I investigated the effects of road traffic and pedestrian disturbance on the distribution, physiology, and reproductive success of birds (with a focus on White-crowned Sparrows, <italic>Zonotrichia leucophrys oriantha</italic>) near the Rocky Mountain Biological Lab in Gothic, Colorado, U.S.A. I conducted 116 point count surveys of breeding birds along a 12 km stretch of an unpaved Forest Service road. Independent of habitat type, the road had a significant effect on the overall number of individual birds (50% more individuals far from the road) that have established breeding territories. The number of species that have higher occurrence rates far from the road was also significantly higher than close to the road. I found and monitored 152 White-crowned Sparrow nests over three years and captured 123 wild sparrows for standardized stress series experiments. I found that the road has a substantial impact on reproductive success primarily due to high rates of nest desertion near the road. I also found that the magnitude of the stress response of male sparrows subjected to an experimental stressor in the field was related to distance to the road and showed an inverse pattern to that of nest success. I also subjected a small number of sparrow nests to an intrusion experiment that consisted of walking in a straight line near the nest four times a day for 15 minutes each time. Sparrow pairs at undisturbed nests were 2.5 times more likely to fledge nestlings successfully than those at disturbed nests. This research will help managers to quantify the effects of human disturbance and to predict the impacts of land-management decisions.