Evaluation of lasers to disperse American crows, Corvus brachyrhynchos, from urban night roosts

Abstract

American crows ( Corvus brachyrhynchos ) have a long history of causing agricultural damage in North America. Shooting and bombing at crow night roosts have been employed to reduce such damage. Most roosts were located in rural locations, but in the latter half of the 1900s crows began to roost in urban locations. Urban crow roosts are presently a nationwide problem in the United States. Thousands of crows at a roost create problems for businesses and residents. Improved control techniques are needed. Lasers have been used in Europe to scare and disperse birds but the technique has only recently received formal testing. We treated urban roosts with lasers to determine if crows react to laser light, can be dispersed from roosts, and whether lasers are effective for eliciting roost abandonment. We treated 63 roosts in Woodland, California and recorded the immediate and short-term reactions of crows. We counted crows at five roosts in Davis, California during an 8-day pre-treatment period and then again during a 4-day treatment period to evaluate crow response to laser treatment. Crows reacted to the laser beam. In Woodland 100% of the crows flew immediately away from 49% of the treated roosts. Between 50% to 99% of all crows flew immediately away at 44% of the treated roosts. At 84% of the roosts crows left without vocalizing and at 95% of the roosts flew directly away without circling overhead. Crows returned to all roosts within 15 min. In Davis there was no difference in the number of crows using roosts during the pre-treatment versus treatment periods. Despite initial dispersal upon treatment, crows reoccupied all treated roosts the same night after treatment. No roosts were abandoned. Therefore, we do not recommend lasers as a stand-alone dispersal tool at urban crow roosts.