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Moe, B., I. Langseth, M. Fyhn, G.W. Gabrielsen and C. Bech (2002). Changes in body conditionin in breeding kittiwakes Rissa tridactyla J. Avian Biol. 33: 225-234..
We investigated the seasonal pattern of changes in body condition of
breeding Kittiwakes Rissa tridactyla in Svalbard (79°N) to evaluate
whether changes in body condition were a consequence of the energetic demands
of breeding (the reproductive stress hypothesis) or of voluntary anorexia
to attain lower flight costs during chick rearing (the programmed anorexia
hypothesis). Adult body condition was recorded from early egg laying to
fledging and was examined in relation to date (relative to hatching), sex,
parental time-budget, brood size and reproductive success. To distinguish
between the two hypotheses we evaluate whether the reduction in body condition
occurred during or ahead of the energetically most demanding part of the
chick-rearing period. We combine our results on changes in body condition
and time-budget with published information on field metabolic rate (FMR)
and chick energy requirements from studies in the same colony.
Our calculations of adult energy requirements and energy intakes indicate
that the first part of the chick-rearing period was energetically the most
demanding period, because adult energy requirement per hour spent off the
nest was highest in this period, and adults were time constrained because
of the need for 24-h brooding of the chicks.
During the incubation period female body condition increased slightly,
but significantly, while male body condition was stable. During the first
part of the chick-rearing period, female and male body condition decreased
by 14.8% and 8.4%, respectively. During the second part of the chick-rearing
period, both male and female body condition remained stable. The reductions
in body condition occurred during the energetically most demanding part
of the chick rearing period, thus supporting the reproductive stress hypothesis.
Parental body condition during the incubation period was positively related
to the probability of successfully fledging young, providing additional
support for the reproductive stress hypothesis.
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