Repeatability in Laying Date and Its Relationship to Individual Quality for Common Murres

Abstract

We studied repeatability and annual variation in laying date and productivity of 37 color-banded female Common Murres (Uria aalge) on Southeast Farallon Island, California from 1986 through 1993 to investigate demographic aspects of individual quality. We substracted the mean population lay date from the lay date of individual females to produce a standardized anomaly statistic. Thirteen birds laid consistently before the population mean, 14 birds were intermediate (showed lay dates which varied earlier and later than annual population means over the study period), and 10 birds consistently laid after the population mean. Repeatability was estimated as 0.204 when excluding the El Niño year of 1992. Chick survival was significantly lower for females which were consistentenly late relative to other members of the population, and for females that laid late within each season. Repeatability, as a measurement of between-individual variation in life history traits, is a useful index to individual quality.