REPRODUCTIVE EFFORT IN ADELIE PENGUINS

We estimated reproductive effort (energy expenditures for reproduction , as opposed to maintenance) in Adelie penguins breeding at Palmer Sta tion, Antarctica. Data on body composition changes and metabolic rate were obtained using isotopic methods. Adelie breeding behavior consist s of an initial courtship stage (during which both sexes fast), incuba tion, the 'guard' stage (when chicks are 1 to 18-28 days old), and the 'creche' stage (from the end of guarding until chicks are 38-45 days old). Both males and females lost considerable mass during the initial stages of the reproductive season, but males fasted longer and lost m ore mass. Mass losses of both sexes consisted of 66% depot fat and 34% lean tissue. Mass and body composition remained constant once birds r esumed feeding. The metabolic expenditure for the foraging necessary t o accumulate the mass lost while fasting - one component of reproducti ve effort - was about 63 MJ in males and 39 MJ in females. Field metab olic rates (FMR) were low during courtship and while incubating, incre asing more than 2-fold when birds resumed foraging. Although mean FMR increased between incubation and the creche stage, differences between stages were small and not significant. We used FMR data and an energy balance model to estimate the cost of feeding chicks. Results suggest a maintenance FMR of about 2.7 x basal metabolism (BMR), increasing t o 3.4-3.6 x BMR during the creche stage. The reproductive effort (as m etabolic expenditures) associated with feeding chicks is 31 MJ (males) to 36 MJ (females). Cumulative reproductive effort is 94 MJ in males and 75 MJ in females, or 5.3-6.2% of the annual energy budget. The rep roductive effort devoted to chick care does not appear to be constrain ed by physiological or time limitations. Instead, selection to reduce the risk of predation may prevent the evolution of increased parental care.