VLECK, C.*; VLECK, D.: Physiological condition and reproductive consequences in Adelie penguins

Animals must make �decisions� (e.g. when or whether to breed, the effort to put into a breeding episode) by integrating physiological, environmental and social inputs. This integration can only be studied in a field context. Physiological measurements that provide reliable predictors of animals’ reproductive decisions will aid in identifying critical input variables and in predicting and potentially managing reproductive success in natural populations. Candidate measurements include body mass and body size, glucocorticoid titers and blood cell counts as indicators of stress, and hematological measures that estimate hydration and reliance of cellular metabolism on stored body fat or protein. In Adelie penguins (Pygoscelis adeliae)reproduction is constrained by foraging ecology, mode of transport, and the latitude at which they live. Females that return to the colony but do not breed are 10-12% lighter than females that do, but male nonbreeders are as heavy as male breeders and have similar hormone levels. Penguins must fast for many weeks during reproduction. Nest failure often occurs when one parent does not return to the colony, and the fasting parent must eventually leave. During normal-length fasts corticosterone levels do not change, but when fasts are very long and birds have lost >35% of their body mass, corticosterone and hematocrit increase and prolactin decreases. During fasting ketone levels gradually increase while uric acid levels are low, but in birds with the longest fasts, ketone levels fall and uric acid levels increase, indicative of a switch from using fat to body proteins for metabolism. These physiological and endocrine measurement help to reveal the proximate mechanisms at the individual level that link environmental and population-level variation in penguin reproductive success.