Experimental Evaluation of Partial Repellent Treatment for Reducing Bird Damage to Crops

(1) In a 0 2-ha flight pen, flocks of twenty brown-headed cowbirds (Molothrus ater Boddaert) and twelve red-winged blackbirds (Agelaius phoeniceus L.) were observed as they foraged on plots sown with rice seed, 0%Y,, 500/1 or 100%/, of which was treated with methiocarb. (2) Seed removal by birds in plots with the 50% and 1000/, treatments was 95-980%o less than that in the 0% groups. Seed handling behaviour did not differ among treatments for either species. (3) These results are consistent with previous experimental findings and with theoretical models of automimicry that predict substantial protection to the entire prey population even when only a small proportion of the prey is unpalatable. (4) Cost-benefit analysis suggests that partial repellent treatment for protection from bird damage, in addition to being environmentally sound, is economically viable in many crops.