Metabolic and hormonal correlates of reproducive effort in the kittiwake (Rissa tridactyla)

Parental effort, the extra energy expenditure above maintenance levels devoted to the care of offspring, has been postulated to incur a fitness cost. Parent birds adjust their daily energy expenditure to the requirements of the brood and a negative correlation between daily energy expenditure during reproduction and subsequent adult survival is expected. Studies conducted on the energetic of breeding kittiwakes have reported a strong repeatability of basal metabolic rate (BMR) between individuals (Bech et al, 1999 Proceeding Royal Society 266: 2161-2167). This suggests that some individuals have consistently higher levels of energy expenditure than others and raises the question of the fitness consequences of having a low or high BMR. The aim of this project conducted in co-operation with Dr. G. W. Gabrielsen and C. Bech, is to study the influence of individual variation in BMR on the ability to provision and rear chicks. To do so, we will measure BMR through the measure of plasma levels of triiodothyronine (T3), which is the metabolically active form of thyroid hormone, in relation to provisioning effort. Provisioning effort will automatically recorded using VHF transmitters and an automatic logging station. For 2002, we will manipulate the level of reproductive effort of the parents through the manipulation of cortcicosterone levels in their chicks. It is known that corticosterone implanted chicks from Kittiwake begg more frequently and that in response, adults increase their provisioning rate (Kitasky et al 2001. Corticosterone facilitates begging and affects resource allocation in the black-legged kittiwake. Behavioral Ecology 12: 619-625). Two groups of chicks will received either an empty (controls group, N=11) or a full subcutaneous corticosterone implants (expérimental group, N=11). Corticosterone implants will be removed after 15 days of experiment.