Which stonechats breed where in Scandinavia?
The European Stonechat Saxicola rubicola is a recent addition to the Scandinavian fauna of breeding birds. But where do they come from? Whereas several studies have failed to find any genetic differentiation, birds of the subspecies hibernans from the British Isles look different from continental birds of the nominate subspecies. In a recent paper, Reino Andersson systematically assessed photos of 404 males during breeding time in Norway, Sweden, and Denmark, and scored six characters that differentiate hibernans and rubicola. In short, the answer is that it varies between the three countries!
In Norway, the majority of the birds match typical hibernans characters, whereas in Sweden most birds look like typical rubicola. Denmark is somewhat intermediate. Interestingly, the few rubicola-like males in Norway are all photographed in the southern and southeastern parts of the country, whereas males in the west coast all look like hibernans. Possibly, Norway was initially colonized from the British Isles, and is now experiencing a second wave of colonization from the continent via the northward expansion on the Swedish west coast (described in another paper by Reino Andersson this year: https://doi.org/10.34080/os.v29.19555).
The main language of this paper is Swedish, but it has an abstract and an extensive summary in English. It is, as always available as Open Access, and is found at https://doi.org/10.34080/os.v29.19691.