Variation in bill colour among Greylag Geese Anser anser breeding in south-west Scania

Abstract

The anser subspecies of the Greylag Goose Anser anser was earlier distributed over most of Europe, between the ranges of sylvestris in the west and rubirostris in the east. Its bill colour was orange. I examined the bill colour of 97 trapped breeding adults from the province of Scania in 1995—1998. I used a six-grade scale from orange (I) to pink (VI). Most birds were intermediate (III), a few had pink bills (V–VI), but none had an orange one (I). Two explanations are examined: fauna falsification by introduction of rubirostris birds, which is known to have taken place several times, and inclusion of rubirostris genes into the small 20th century population of anser birds by rubirostris individuals that have reached the anser range naturally; a few such winter visitors are known. I conclude that the most likely explanation is the deliberate introduction of rubirostris but the other alternative cannot yet be ruled out.