Dimorphism in Stercorarius pomarinus (Temminck)

• Published in: Ibis
• Main Author: Southern, H. N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1944
• Subjects: Arctic; Greenland; Mackenzie River; Arctic skua; Mackenzie river; Novaya Zemlya; Stercorarius pomarinus; Alaska
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1944.tb07528.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1944.tb07528.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1944.tb07528.x

SUMMARY. Records from the literature are collected about the proportions of dark and pale forms of the Pomatorhine Skua. The breeding range falls into two areas, one from Novaya Zemlya to north‐west Alaska, the other from the Mackenzie River to west Greenland. In both these areas dark birds are evenly distributed in the proportion of 1 in 5–20, though there is a slight suggestion that they. are less common in the second than in the first region. This even, distribution contrasts with tile cline in dimorph‐ratio known to exist in the Arctic Skua. Pomatorhine Skuas fluctuate in breeding strength from year to year. This is probably connected with the lemming cycle.