ENERGETICS OF SWIMMING BY THE PLATYPUS ORNITHORHYNCHUS-ANATINUS - METABOLIC EFFORT ASSOCIATED WITH ROWING

The metabolism of swimming in the platypus Ornithorhynchus anatinus Sh aw was studied by measurement of oxygen consumption in a recirculating water flume. Platypuses swam against a constant water current of 0.45 -1.0ms(-1). Animals used a rowing stroke and alternated bouts of surfa ce and submerged swimming. Metabolic rate remained constant over the r ange of swimming speeds tested. The cost of transport decreased with i ncreasing velocity to a minimum of 0.51 at 1.0ms(-1) Metabolic rate an d cost of transport for the platypus were lower than values for semiaq uatic mammals that swim at the water surface using a paddling mode. Ho wever, relative to transport costs for fish, the platypus utilized ene rgy at a similar level to highly derived aquatic mammals that use subm erged swimming modes. The efficient aquatic locomotion of the platypus results from its specialised rowing mode in conjunction with enlarged and flexible forefeet for high thrust generation and a behavioral str ategy that reduces drag and energy cost by submerged swimming.