Recruitment of Cassin's Auklet (Ptychoramphus aleuticus): Individual Age and Parental Age Effects

Recruitment is an important aspect of life history that is difficult to estimate without long-term data. We used 28 years of data to create multistate capture—mark—recapture models with maturity status as state to provide estimates of age-dependent probabilistic recruitment (transition from juvenile to breeder state) of Cassin's Auklets (Ptychoramphus aleuticus) breeding at Southeast Farallon Island, California. We found strong evidence for age effects in recruitment and survival, but not in breeding propensity. We also examined parental-age effects on return rate of offspring. Although an average of 70% of a cohort begins breeding by age 4, fledglings from 2- to 4-year-old mothers were less likely to become breeders than fledglings produced by older mothers. This may be attributable to age-related differences in egg production and maternal offspring-rearing abilities that could contribute to differences in fledgling recruitment rates. Eggs of younger mothers had lower volume and their fledglings had lower mass than those of older mothers. We suggest that researchers, managers, and population modelers consider the possibility that young breeding birds that successfully fledge young do not always produce viable offspring that will become breeders.