Rufous Common Cuckoo chicks are not always female

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this recordThe Common Cuckoo (hereafter Cuckoo) shows two adult plumage morphs—adult male plumage is grey and adult females are either grey or, less frequently, rufous. The situation is less clear in juveniles, as both sexes exhibit variable proportions of grey and rufous colour. We thus describe the patterns related to sex-specific plumage colour variation in a central European Cuckoo population. We genetically determined the sex of 91 Cuckoo chicks and using visual classification of photographs we scored juvenile plumage colouration of individual chicks into five classes based upon the increasing proportion of rufous colour on feathers. To verify these scores, we sampled chick feathers and quantified the proportion of rufous colour of individual feathers by digital image analysis. We found that juvenile females had a higher proportion of rufous colour of feathers than juvenile males. However, the difference was marginally non-significant based on visual inspection alone, and some male chicks even showed intensively rufous plumage like those of juvenile females. In contrast, we captured only grey adult males (n = 37), while five out of 20 adult females were rufous. The rufous colour of Cuckoo feathers considerably differed from the grey colour and the difference seemed to be larger in adults than in juveniles. We show that chicks, unlike adult females, cannot be visually assigned to either of the adult morphs. Therefore, we encourage further investigation of Cuckoo plumage colouration across the species’ range to examine the process of plumage maturation. A detailed genetic analysis is necessary to understand the origin of Cuckoo feather colouration.This study was supported by the Czech Science Foundation (project 17-12262S) and by the Institutional Research Plan (RVO: 68081766)

Magnitude and direction of population trends, ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012

Magnitude and direction of population trends (1 = 100%), ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012. Non-breeding niche position varies from 1 (closed forest) to 7 (open country) and non-breeding niche breadth expresses the difference between the values of the two main habitats; non-breeding habitat wetness scores from (1) dry to (3) aquatic habitats. Non-breeding regions: (1) west–central region, (2) west–east region, (3) central–south region, (4) ‘entire’ region. Breeding habitat: forest (F), wetland (W), urban (U) and open habitat (O). PC 1 expresses a gradient from ‘slower strategy’ (K-selected) species to ‘faster strategy’ (r-selected) species. PC 2 depicts a gradient from species allocating most of their energy to just one breeding attempt per season to species spreading their investments across multiple breeding attempts per season