A Successful Mixed Brood between Eurasian Nuthatches Sitta europaea and Eurasian Blue Tits Cyanistes caeruleus

Successful mixed broods in hole-nesting passerines are relatively rare. Increased competition for nesting sites may result from environmental conditions that constrain the breeding period, bringing in contact species that would normally rarely interact. Meteorological conditions preceding the breeding period of 2024 could have delayed the reproduction of Eurasian Nuthatches Sitta europaea relative to Eurasian Blue Tits Cyanistes caeruleus in our study area. Here we report the first case of a successful mixed brood involving Eurasian Nuthatches and Blue Tits. On 4 May, we observed a Blue Tit hatchling in a Nuthatch nest. The Blue Tit, reared in the foster nest, had smaller tarsus and wing length relative to the average measures of all observed Blue Tit nestlings in 2024. However, its mass was in the normal range, and it fledged successfully, along with five Nuthatch ‘siblings’.