Fitness relationships.--We captured nesting females on the breeding grounds near Oliktok, Alaska, and measured body mass, flattened wing length, exposed culmen length, tarsus length, head-bill length, and TOBEC. Thereafter, we recaptured each female at approximately weekly intervals during incubation for additional body mass and TOBEC measurements.
Total body electrical conductivity (TOBEC) to estimate total body fat of free-living birds.
After measuring live body mass and TOBEC for the final time on 22 February 1992, we removed the tags and took additional TOBEC readings of the birds without their tags ([greater than or equal to] 3 readings).
The live body mass and TOBEC measurements taken on 22 February and the results of fat extractions were used to develop calibration equations (multivariable regression models) to predict lipid mass of birds during previous weeks of the study (Morton et al., 1991; Osborne, 1993).
We tested differences between TOBEC readings of birds with and without their tags for significance using a two-way ANOVA that examined the differences attributed to individual birds and tags (PROC GLM; SAS Institute Inc., 1985a).