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Résumé :
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[Nest defence behaviour of four corvid species towards a common foe, the carrion crow, was examined. The various species responded quite differently when a caged crow was presented near the nest. Compared with the other species magpies attacked the caged crow most often. Rooks were very vociferous and circled much above the crow. Jackdaws usually perched nearby; occasionally, they circled over and scolded at the crow. Crows flew off and frequently started to forage at a distance, behaving as though nothing alarming was happening near their nest. These differences in nest defence behaviour have been related to inter- as well as intraspecific variations in nesting conditions, including accessibility, camouflage, site, dispersion and construction of nests. Behavioural responses and nesting conditions are finely tuned and can be considered as elements of adaptive complexes promoting the safety of the nest.]
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