We investigated whether brood value (laying date, brood size, nestling age and condition) and parental quality (condition, male badge size) affect experimentally provoked nest defence in House Sparrows in the Czech Republic. We included the badge size (a melanin-based throat feather patch) because it serves as a signal of social status, age and condition. We presented a stuffed Black-billed Magpie Pica pica to 19 pairs of sparrows. To assess the defence intensity we used the “risk index”, increasing with time spent reacting and riskiness of the reaction (number of approaches and attacks), while declining with increasing distance from the predator. Females did not adjust their nest defence to the brood value and males did so only partially, tending to defend the early broods more intensely, which marginally supports the “value of offspring hypothesis”. The birds did not adjust their nest defence to quality or defence intensity of their partners, thus the “differential allocation hypothesis” was not supported. Male nest defence was more intense than in females and increased with male badge size. As male contribution to nest defence may affect the breeding success, we hypothesize the badge size could be used as a signal of nest defence intensity used by females.
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Vol. 46 • No. 1