RESPONSES OF CAPTIVE FISH CROWS TO EGGS TREATED WITH CHEMICAL REPELLENTS

Eggs of many bird species are subject to predation by corvids. To eval uate whether predation might be reduced through food avoidance learnin g, we offered Japanese quail (Coturnix japonica) eggs treated with var ious repellent chemicals to captive fish crows (Corvus ossifragus). To pically applied methyl anthranilate (100 mg/egg), alone and in combina tion with injected methiocarb (18 mg/egg), effectively reduced (P = 0. 015) egg eating by crows. Crows that received topical methyl anthranil ate alone, however, lost their avoidance response when untreated eggs were offered. Egg eating was not reduced (P > 0.05) by 18 mg/egg injec tions of carbachol (carbamylcholine chloride) or methiocarb, or by a c ombined methiocarb (18 mg/egg) and methyl anthranilate (100 mg/egg) in jection. Crows exposed to eggs injected with elevated levels of carbac hol (40 mg/egg) or methiocarb (30 mg/egg) ate more eggs (P = 0.046) th an did crows that received topical methyl anthranilate treatments. Inj ected eggs might be more suitable for field use, however, because they are difficult to distinguish from untreated eggs and they are easier to prepare. The persistence displayed by some crows during their 5-day exposure to treated eggs suggests that successful application of repe llent egg treatments will require an extended period of training for t arget predators to acquire an avoidance response.