Expenditure, investment, and acquisition of energy in southern elephant seals

Information on the expenditure and investment of energy in southern elephant seals, Mirounga leonina , was collected during breeding and molt over four field seasons at South Georgia. Weight and body composition changes of mothers, pups, and breeding males were monitored during the breeding season. These changes were also measured in adult females, before and after the 70-day period when animals fed at sea between breeding and molt. During this period, information on foraging movements and behavior was gathered using purpose-built satellite-relay data loggers. Body composition changes were measured using isotope dilution techniques. Breeding energetics information is discussed in relation to the evidence for differential investment in male and female pups. Large females produce larger pups, both at birth and weaning. Male pups are born larger than female pups. However, there is no evidence that mothers invest more energy (either relative or absolute) in male pups after birth once female size and birth weight are taken into account. Foraging movements and diving behavior are discussed in terms of the oceanography of the foraging area and possible constraints placed by prey consumption on the seals' dive behavior. We suggest that the long distance travel of females to distant feeding locations may be advantageous in providing for the requirements for reliable food sources in a long-lived, uniparous mammal. Dive characteristics changed during the different phases of activity in foraging animals in relation to the average daily velocity of the animal, water depth, and undersea topography.

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