THE EFFECT OF RENESTING ABILITY AND NESTING ATTEMPT ON EGG-SIZE VARIATION IN WILLOW PTARMIGAN

Interclutch variation in the size of free-living willow ptarmigan (Lag opus lagopus alexandrae) eggs was examined at Chilkat Pass, British Co lumbia. Egg volume (19.9 +/- 0.1 cm(3); mean +/- 1 SE) fell within the range reported for other populations of ptarmigan. Most of the egg-si ze variation (56.0%) was explained by differences among females, but r enesting ability and nesting attempt were also important. The age-clas s of females and timing of nest loss had no effect on egg-size variati on. Females that laid replacement clutches produced eggs in their firs t nesting attempts (n = 12 females, 102 eggs) that were 4.6% (0.9 cm(3 )) larger than the eggs of birds that did not renest (n = 12 females, 95 eggs). Clutch size decreased between nesting attempts, and there wa s a 1.6% (0.3 cm(3)) increase in egg size (n = 12 females, 65 eggs). W e suggest that future studies examining the influence of nesting attem pt on egg size should also control for renesting ability.