Dune Larks (Mirafra erythroclamys) are the only avian species that has evolved the capability of surviving in the Namib Sand Sea, one of the driest regions in the world. Their field metabolic rate (FMR) and water flux, as measured by doubly labelled water, during the breeding and non-breeding season are reported here. Keywords: Desert, doubly labelled water, energetics, field metabolic rate, incubation, water flux.