Chappell MA, Janes DN, Shoemaker VH, Bucher TL, Maloney SK (1993).
Reproductive effort in Adélie Penguins. Behavioral Ecology and
Sociobiology 33:173-182.
ABSTRACT -- We estimated reproductive effort (energy
expenditures for reproduction, as opposed to maintenance) in Adélie
penguins breeding at Palmer Station, Antarctica. Data on body composition
changes and metabolic rate were obtained using isotopic methods. Adélie
breeding behavior consists of an initial courtship stage (during which both
sexes fast), incubation, 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
more mass. Mass losses of both sexes were comprised of 66% depot fat and
34% lean tissue. Mass and body composition remained constant once birds
resumed feeding. The metabolic expenditure for the foraging necessary to
accumulate the mass lost while fasting -- one component of reproductive
effort -- was about 63 MJ in males and 39 MJ in females. Field metabolic
rates (FMR) were low during courtship and while incubating, increasing 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 to 3.4-3.6 X BMR during the creche
stage. The reproductive effort (as metabolic 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 reproductive effort devoted to chick care does not appear
to be constrained by physiological or time limitations. Instead, selection
to reduce the risk of predation may prevent the evolution of increased parental
care.