Meeting Abstract
While the number of young produced per nesting pair (i.e., fledging success) is often used as a proxy for recruitment in seabird populations, post-fledging survival is likely to be much lower than this estimate suggests. Mortality is difficult to measure accurately once juveniles disperse from the breeding site; however, accounting for differences in fledgling physical condition can expose variation in survival probability not captured by fledging success alone. To assess inter- and intra-colony variation in nestling condition, we collected measures of short-term (relationship of mass to skeletal size) and long-term (corticosterone levels in body feathers) physical condition of 3-6 week-old chicks from pelican colonies across the northern Gulf of Mexico over a three-year period. We found that the overall negative relationship of corticosterone to body condition was strongest in younger chicks and at colonies experiencing nutritional stress. As chicks reached fledging, corticosterone levels remained highest in food-limited colonies but were more likely to reflect colony- and nest-specific variables such as colony size (intraspecific competition), hatch order, and nest site location. Since elevated stress levels during development are known to affect lifetime survival and reproductive fitness, we suggest nestling feather corticosterone as a useful index of developmental conditions and post-fledging survival probability that may capture additional information not reflected in short-term measures of physical condition.
