ENERGETICS OF BURROWING, RUNNING, AND FREE-LIVING IN THE NAMIB DESERTGOLDEN MOLE (EREMITALPA-NAMIBENSIS)

The Namib Desert golden mole (Eremitalpa granti namibensis) is a small (c. 20 g), blind, sand-swimming, chrysochlorid insectivore that inhab its the sand dunes of one of the driest and least productive areas of the world, Its food, largely termites, is sparse and occurs in widely distributed patches, and free water is unavailable. The moles forage b y running on the surface and burrowing below the sand. We estimated th eir daily energy expenditure in the field to be 11.8 kJ d(-1) by const ructing a 'distance-energy budget' based on measurements of tracks in the sand and the energy cost of running (4.2 kJ d(-1)), burrowing (3.2 kJ d(-1)), and resting (4.4 kJ d(-1)). We also measured field metabol ic rate (12.5 kJ d(-1)) and water turnover (2.3 ml d(-1)) independentl y with doubly-labelled water. The resting metabolic rate (0.5 ml O-2 g (-1) h(-1) at 35 degrees C) is about a fifth of that predicted for a n ormal insectivorous mammal, and the daily field energy expenditure and water turnover are about a half. The low daily energy expenditure ste ms mainly from the low resting metabolic rate, which is associated wit h low body temperatures and metabolic depression. Moles save more ener gy during foraging by running on the surface of the sand, rather than burrowing under it. The gross energy cost of sand-swimming (80 J m(-1) ) is 26 times more expensive than running on the surface (3.0 J m(-1)) , but is less than a tenth of the energy required by mammals that tunn el through compact soil. Nevertheless, it would be energetically impos sible for the moles to obtain enough food by foraging only underground at our study site. The mean track length was 1.4 km, but only 16 m of it was below the surface. There is evidence that the track length and fraction underground depend on food abundance which is influenced by rainfall.