Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2 ALISAUSKAS, RAY T. Prairie and Northern Wildlife Research Centre, Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, Saskatchewan, Canada S7N 0X4 We studied various aspects of the breeding biology of king eiders (Somateria spectabilis) nesting at Karrak Lake, south of Queen Maud Gulf in the central Canadian Arctic. We found 41 nests distributed among 10 islands in Karrak Lake; to our knowledge, this represents the largest number of king eider nests studied at one site. We suspect that island-nesting by king eiders is more common than has been previously reported. King eiders favoured mid-sized islands (0.002 - 0.081 km?) favoured over very small (<0.002 km?) or very large (>0.081 km?) islands. Mean clutch size was 5.4 Ò 1.7 (SD) eggs. Apparent nest success was 69.4%, with a composite Mayfield estimate of nest success over egg laying and incubation of 48.7% (95% CI: 47.4 - 50.0%). Nest success was uncorrelated with date of nest initiation or island size, but eiders nesting on islands farther from the mainland had increased success over those nesting on islands closer to the mainland. Additionally, nest success was greater on islands with more nesting eiders and on islands with nesting arctic terns (Sterna paradisaea).