PARENTAL INVESTMENT BY THE SEXES IN THE HERRING GULL - THE USE OF ENERGY RESERVES DURING EARLY BREEDING

A sample of culled birds was used to determine weight change and size of endogenous nutrient reserves in male and female Herring Gulls Larus argentatus during the period from colony occupation to late incubation. Both sexes showed considerable variation in body condition according to breeding phase. The most striking difference between the sexes was found in lipid contents prior to laying. Whereas males tended to deplete endogenous fat, females gained fat. There was no marked change in protein reserves in either sex. It is concluded that males meet maintenance costs during courtship feeding by using a great deal of their endogenous fat while saving the proteins. This is done in favour of the body condition of the laying female, males thus equalizing the initial parental investment of the two sexes. Both sexes regained energy reserves during incubation, being in equal physiological condition when the chicks hatched.