干旱区生态环境知识资源中心

1. 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.

2. FMR is relatively constant over the annual cycle, which conforms to the ’reallocation hypothesis’. With data pooled for both seasons, males expended energy at a rate of 97.5 +/- 20.4 kJ day(-1) (+/- SD) and females at 87.5 +/- 13.0 kJ day(-1). The data supported the hypothesis that Dune Larks do not possess a reduced FMR, a result attributable to their elevated basal metabolism. In a previous laboratory investigation, Dune Larks had a low rate of evaporative water loss despite their elevated basal metabolic rate (BMR). The present study demonstrated that this low evaporative water loss translates into a low water influx in the field.

3. The FMR of Dune Lark females equalled 88.1 +/- 6.9 kJ day(-1) during incubation, and 88.5 +/- 9.9 kJ day(-1) when they were feeding 8-10-day-old nestlings. These data do not support the idea that the incubation period is a time of low energy demand.

4. Dune Larks had a relatively constant water influx throughout the year. For sexes combined, mass-adjusted values of water influx averaged 0.59 ml H2O/(day mass(0.682)).

5. Calculations showed that neonates received 10 kJ day(-1) whereas towards the end of the nestling period, chicks were fed 75 kJ day(-1), the maximum gross energy intake for nestlings. During chick rearing, males increased the amount of food that they found by 57.7%, females by 64.3%, late in the nestling period.

6. Dune Larks foraged in the morning and late afternoon, but were constrained by their environment to seek shade at midday during the breeding season.

7. Metabolic water production plays a significant role in the water economy of Dune Larks. Assuming a mixed diet, 47% of their water intake comes from the oxidation of food stuffs.