Estimating repeatability of egg size

Measures of repeatability have long been used to assess patterns of variati on in egg size within and among females. We compared different analytical a pproaches for estimating repeatability of egg size of Black Brant. Separate estimates of repeatability for eggs of each clutch size and laying sequenc e number varied from 0.49 to 0.64. We suggest that using the averaging egg size within clutches results in underestimation of variation within females and thereby overestimates repeatability. We recommend a nested design that partitions egg-size variation within clutches, among clutches within femal es, and among females. We demonstrate little variation in estimates of repe atability resulting from a nested model controlling for egg laying sequence and a nested model in which we assumed laying sequence was unknown.