Female Blackbirds’ Response to Stress during Breeding: Possible Implications for Future Management

Abstract

Blackbirds are reported to cause between 1-2% crop damage per year, but the distribution of damage is not uniform, with some fields this number can be as high as 20%. With many consumers in today’s market concerned with animal welfare, nonlethal management techniques have become more important. Many of these techniques exploit natural predator-prey systems. One area of research that has not been previously addressed is the physiological response of birds to visual and auditory scare devices designed to imitate predators. The current project is part of a series of studies that aim to develop knowledge of both physiological and behavioral trade-offs of female red-winged blackbirds when exposed to predation risk as a chronic stressor. Breeding colonies were exposed to an avian predator, avian nest parasite, or a non-threatening avian effigy with corresponding bird call at the beginning of the breeding season. Behavioral responses were monitored across the season, including general response to the predators and reproductive trade-offs. We predicted that female response to perceived predation risk would be greater than response to parasites or control treatments, and that females would make a greater reproductive trade-off in favor of future breeding seasons when presented with the perceived risk and stress of predation. Results suggest that red-winged blackbirds do have a greater response to the perceived risk of predation than to the parasites or control treatments. In terms of nest success and lay date, females do not seem to have different reproductive behavioral trade-offs under different treatments. However, there is a trend for larger clutches in nests found within the predator treatment, suggesting that females may actually be making a trade-off for the current rather than future seasons. Future work will focus on analyzing the physiological trade-offs that females make during the breeding season, especially while under chronic stress of predation risk. Results will help provide a basis for applied research aimed at improving bird damage management.