Langseth, I., B. Moe and C. Bech (2001). Reduction in body mass and basal metabolic rate in breeding female Kittiwakes (Rissa tridactyla); an adaptation to reduce maintenance costs? Atlantic Seabirds 3: (in press).

We studied changes in body mass and basal metabolic rates (BMR) in breeding female Kittiwakes (Rissa tridactyla) on Svalbard (79oN 12oE) in 1997 and 1998. Measurements of body masses and BMR were obtained two weeks before the time of hatching, at hatching, early in the chick-rearing period and late in the chick-rearing period.
During the incubation period the body mass and mass specific BMR remained relatively stable. From hatching to late chick-rearing both body mass and mass specific BMR decreased by 12% and 26% respectively. However, from about two weeks up to about four weeks into the chick-rearing period, body mass and BMR did not change significantly. Whole body BMR scales with body mass2.18. This exponent is greater than that expected for a homomorphic variation in BMR, and indicates that the reduction in BMR must involve other properties than an overall body mass reduction.
The simultaneous reduction in body mass and BMR could result from a negative energy balance, leading to a reduction in the masses of metabolically active organs. Alternatively, a reduction in BMR could be an adaptation to compensate for an elevated activity level during the chick-rearing period. By a reduction in the adultís maintenance costs, more energy can be allocated for promoting chick growth.