Individual study: Impact of treatment with methiocarb on common raven Corvus corax predation of eggs in least tern Sterna antillarum colonies at Camp Pendleton, California, USA
Avery M.L., Pavelka M.A., Bergman D.L., Decker D.G., Knittle C.E. & Linz G.M. (1995) Aversive conditioning to reduce raven predation on California least tern eggs. Colonial Waterbirds, 18, 131-138
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Use aversive conditioning to reduce nest predation by avian predators
A replicated, randomised and controlled before-and-after experiment in California, USA, in 1991 (Avery et al. 1995) found that significantly fewer Japanese quails’ Coturnix japonica eggs were taken by ravens Corvus corax from artificial nest scrapes in a ‘test period’ following a ‘training period’ (approximately two weeks), when eggs were treated with methiocarb than during the training period itself (0-33% of eggs taken during the test vs. 9-67% during training). Fewer eggs were taken from four sites that contained treated eggs over the test period, compared to sites where eggs were untreated in the test period, but had been treated during training (3% of eggs taken at one of four treated sites only vs. 0-33% taken at untreated sites). A follow-up experiment found that one of the eight raven pairs previously conditioned to avoid quails’ eggs resumed predation of eggs (both treated and control eggs) when they were placed in a simulated Californian least tern Sterna antillarum browni colony. A further experiment found that when methiocarb-treated eggs were presented at ten sites within three least tern colonies in 1992, a total of 20 eggs were removed or broken over 1,450 ‘egg days’ and no tern eggs were predated by ravens at any of the colonies in 1992.