Gs. Fowler et al., REPRODUCTIVE ENDOCRINOLOGY AND WEIGHT CHANGE IN RELATION TO REPRODUCTIVE SUCCESS IN THE MAGELLANIC PENGUIN (SPHENISCUS-MAGELLANICUS), General and comparative endocrinology, 94(3), 1994, pp. 305-315
The Magellanic penguin is a colonial monogamous species that lays only
a single clutch of two eggs per year. However, failed breeders remain
at the colony and engage in nest building, fights, and copulations wi
thout relaying. The seasonal changes in reproductive hormones and body
weight through the nesting cycle were studied, with respect to the re
productive success or failure of individuals. Body weight changed dram
atically in both sexes through the season, in response to fasting duri
ng incubation, and high body weight in males at the onset of incubatio
n was a strong predictor of eventual reproductive success. Circulating
steroid hormones had a biphasic seasonal pattern, with elevated level
s during the sexual phase of breeding (prior to egg laying), declining
to low, stable levels during the parental phase after eggs were laid.
Luteinizing hormone levels were elevated in females, but not in males
, prior to egg laying. Both sexes responded to reproductive failure by
increasing the secretion of testosterone, and females also increased
the secretion of estradiol, a response that would be expected of a spe
cies that can renest following failure. However, renesting is extremel
y rare, and this hormonal response to failure may instead serve to pro
mote maintenance of pair bonds and also territory ownership across yea
rs, (C) 1994 Academic Press, Inc.