Birds frequently use mobbing as a nest defense strategy and the intensity of reaction depends on various factors, e.g., predator species and its distance from the nest. We tested the dynamic risk assessment hypothesis, that is, whether Blackbirds adjust their nest defense to the distance of a predator, Black-billed Magpie Pica pica, from their nest. Responses to a magpie dummy and a Rock Pigeon Columba livia dummy were investigated during the breeding period in an urban environment. The dummies were presented at two different distances, near (1.5 m) and far (6-7 m) from the nest. We also tested the relationship between the sex of a parent and the intensity of mobbing in nest defense. The intensity of mobbing reaction in either parent was highest for the magpie dummy near the nest, although the males showed higher overall intensity than females. When the magpie dummy was far from the nest, the birds preferred hiding in vegetation to mobbing. The highest intensity of vocalization was induced by the magpie dummy near the nest and the lowest by the pigeon dummy. Both parents used "chink" calls more frequently with the magpie dummy near the nest compared to the dummy far from the nest. The "seee" calls were used mostly in response to a distant magpie dummy. The reaction to a pigeon dummy was generally weak, which shows that the birds clearly discriminated between the dummies of the predatory magpie and the harmless pigeon.
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