Breeding biology of Steller's eiders (Polysticta stelleri) near Barrow, Alaska, 1991-99

The breeding biology of Steller's Ciders (Polysticta stelleri) near Barrow, Alaska, was studied from 1991 to 1999. The number of nests found per year ranged from 0 to 78. Mean clutch size was 5.4 (SD = 1.6, n = 5 1), incubation period was 24 days, and Mayfield nest success ranged from 0 to 35%. Egg survival was 24% overall (n = 45 1). Most nests were found on the rims of low-centered polygons near ponds with emergent vegetation. Marked broods remained within 700 rn of their nest sites, and duckling survival was low. Steller's ciders nested in five of the nine years studied, corresponding with years of high lemming density and nesting pomarin jaegers (Stercorarius pomarinus) and snowy owls (Bubo scandiacus). Steller's eiders may choose to nest only in years with abundant lemmings for two reasons: first, abundant lemmings provide an alternative prey source for foxes and other predators of ciders; second, jaegers and owls defending their own nests may inadvertently provide protection to ciders nesting nearby.