Ardea
Official journal of the Netherlands Ornithologists' Union

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Salathe T. (1987) Crow predation on Coot eggs: effects of investigator disturbance, nest cover and predator learning. ARDEA 75 (2): 221-229
Predation by Carrion Crows Corvus c. corone of Coot Fufica atra eggs was studied in the Camargue wetland region of southern France. The main emphasis was put on testing to what degree differences in nest cover influence the possibility of predation, what impact regular nest visits have on predation frequency and in what manner crows react to the investigator. Nests were visited at 10 day intervals on three marshes differing in vegetation structure, and additional nest visits were undertaken daily at one of them. Regular observations from an elevated platform revealed the degree of egg predation without human disturbance. This was 18% of the eggs laid under the given conditions (about 1 crow /10 ha. 10 Coot pairs). Nest success was highest on the marsh with dense Phragmites reeds, followed by the marsh with Tamarix trees which Coots used for nesting and then the marsh with open reed beds of Typha and Scirpus. Within a marsh or vegetation unit nest cover did not affect the chances of predation. Although regular nest visits increased predation of clutches, this was significant only for daily nest visits where crows specialised on egg predation. Crows found artificial clutches within 5 hours and developed a specific searching image for them in heavily disturbed marshes. Thus frequent nest visits may influence the behaviour of individual crows to such an extent that they prevent reliable research on the breeding ecology of the Coot population.


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