ENERGY-EXPENDITURE, BODY-WEIGHT AND FORAGING PERFORMANCE OF STORM-PETRELS HYDROBATES-PELAGICUS BREEDING IN ARTIFICIAL NESTING CHAMBERS

Many avian species, such as Storm Petrels Hydrobates pelagicus, are in tolerant of disturbance at the nest, which complicates the collection of data relating to metabolic rate and the use of body reserves during incubation. I describe the design of an artificial nest chamber, whic h is simple and inexpensive to construct and facilitates the collectio n of such data, Eighty-one nest chambers situated in a large colony of breeding Storm Petrels had high occupancy rates (29/81 in each of 2 y ears), and the breeding success of birds nesting in boxes was similar to that of pairs nesting in natural crevices. Direct measurement of ca rbon dioxide production using standard respirometry techniques and est imations of metabolic rate based on the rates of mass loss during incu bation indicated close agreement between the two methods of estimating energy consumption, Assuming the metabolic requirements during incuba tion are furnished entirely from stomach oil, 76% of the daily mass lo st represented stomach oil catabolism. The duration of incubation shif ts was unrelated to the body mass, and presumably to body reserves, of Storm Petrels on arrival at the nest, Shifts were usually terminated by the return of the foraging partner. The body mass of birds returnin g from foraging was relatively constant and was unrelated to the amoun t of time spent foraging at sea, indicating that the decision rule to return from foraging was the acquisition of a threshold level of body mass (about 31 g). There was a negative relationship between the durat ion of foraging trips and the body mass of Storm Petrels at departure from the nest and a positive relationship between trip duration and th e net mass gain at sea. The use of nestboxes based on the design descr ibed here would have a wide variety of applications in facilitating da ta collection for many cavity- or burrow-nesting species which are sen sitive to disturbance.