Individual study: Corvid removal does not increase nesting success in black grouse Tetrao tetrix or willow ptarmigan Lagopus lagopus in Norway
Parker H. (1984) Effect of Corvid Removal on Reproduction of Willow Ptarmigan and Black Grouse. The Journal of Wildlife Management, 48, 1197-1205
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Control avian predators on islands
A controlled study on Karlsøy Island (7.7 km2), Norway, in 1978-81 (Parker 1984), found that removing hooded crows Corvus cornix and ravens Corvus corax from an experimental area did not decrease predation of black grouse Tetrao tetrix nests, compared to control areas (49 nests studied). Predation of willow ptarmigan Lagopus lagopus nests was lower in the first year of the experiment (21 nests studied) but not in the next three (total of 214 nests). The author suggests that compensatory predation by ermine Mustela erminea may have prevented corvid removal from having an effect. Corvids were removed by poisoning with alpha-chloralose-treated eggs and shooting.