REPRODUCTIVE ENERGETICS OF A FREE-LIVING BIRD

The D2O18 technique was used to estimate the average daily metabolic rate [ADMR] of adult house martins (Delichon urbica L.) during the breeding season. The rate at which adults fed broods and the fecal output of different-sized broods were observed. The ADMR of house martins feeding young was 2.22-5.27 .times. SMR [standard metabolic rate] with a mean of 3.89 .times. SMR. The ADMR of male birds feeding broods of large biomass was greater than that of males feeding broods of small biomass; there was no difference in the ADMR of females feeding large and small broods. This pattern of energy expenditure is related to the work done in raising the brood as reflected in feeding visits. The food demand and feeding rate was the same for 1st and 2nd broods of similar size. The energy expended by the adults on the overall mean brood size of 3.29 was 35.02% higher during 2nd brood rearing than during first. The extra energy expended during 2nd brood rearing may be due to a change in foraging techniques brought about by changing environmental conditions.