| Summary: | Multiple raptors show juvenile plumage that is substantially different from that of their parents. Here, we test the prediction that the colouration of the juvenile northern goshawk ( Accipiter gentilis ) resembling the colouration of the common buzzard ( Buteo buteo ) acts as a form of aggressive mimicry. The goshawk specialises in hunting larger birds and mammals up to the size of geese or hares, while the buzzard preys mostly on small rodents. Potential prey may thus consider juvenile goshawks as less dangerous raptors, and the juvenile goshawk may thus gain an advantage when hunting. We used the Eurasian magpie ( Pica pica ), a common prey of the goshawk, to test this prediction. We compared the behavioural responses of magpie parents defending their freshly fledged young towards stuffed dummies of an adult goshawk, juvenile goshawk, and buzzard. To be able to assess whether this behaviour differs from responses to a nest predator and a harmless bird we also presented a common raven ( Corvus corax ) and common pheasant (Phasianus colchicus) as baseline stimuli. The overall intensity of antipredatory behaviour towards the juvenile and adult goshawks did not differ, but magpies took more risks facing juvenile goshawks. Additionally, the intensity of antipredatory behaviour towards the juvenile goshawk was higher than towards the buzzard, but the willingness to take risks did not differ in relation to the two predators. The overall intensity of antipredator behaviour thus supports the conclusion that magpies do not distinguish between juvenile and adult goshawks, while they do distinguish juvenile goshawks from buzzards. Conversely, the willingness to take risks supports the conclusion that magpies do not distinguish juvenile goshawks from buzzards. Funding provided by: University of South Bohemia in České Budějovice Crossref Funder Registry ID: https://ror.org/033n3pw66 Award Number: 14/2022/P
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