BREEDING BIOLOGY OF KING-EIDERS NESTING ON KARRAK LAKE, NORTHWEST-TERRITORIES

We studied various aspects of the breeding biology of king eiders (Som ateria spectabilis) nesting at Karrak Lake, south of Queen Maud Gulf i n 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 report ed. King eiders favoured mid-sized islands (0.002 - 0.081 km(2)) over very small (less than 0.002 km(2)) or very large (greater than 0.081 k m(2)) islands. Mean clutch size was 5.4 +/- 1.7 (SD) eggs. Apparent ne st success was 69.4%, with a composite Mayfield estimate of nest succe ss over egg laying and incubation of 48.7% (95% CI: 47.4 - 50.0%). Nes t success was uncorrelated with date of nest initiation or island size , but eiders nesting on islands farther from the mainland had greater success than those nesting on islands closer to the mainland. Addition ally, nest success was greater on islands with more nesting eiders and on islands with nesting arctic terns (Sterna paradisaea).