Low field metabolic rates for geckos of the genus Rhoptropus may not be surprising

•Rhoptropus bradfieldi has a field metabolic rate 26% that of a typical desert lizard of the same size.•Rhoptropus bradfieldi may source a significant proportion of its water budget from episodic fog events.•Differences in habitat and morphology may affect the energetics of closely related Rhoptropus species.•Rhoptropus bradfieldi forages on arthropods using a sit-and-wait foraging strategy.

Geckos of the genus Rhoptropus are small diurnal lizards occurring in arid regions of Namibia and Angola, and are not well studied relative to other desert lizards. Rhoptropus afer has a field metabolic rate significantly lower than that of other desert lizards, but comparable studies have not been carried out in any other Rhoptropus species. We examined the field metabolic rate, water turnover, foraging behavior, and thermal biology of Bradfield's Namib day gecko, Rhoptropus bradfieldi, in the Namib Desert. This species occupies rocky habitats and feeds on arthropods via a sit-and-wait strategy. We found that it has a field metabolic rate (140 J d−1) that is 26% that of a typical desert lizard of the same size (540 J d−1). We also found that R. bradfieldi had a relatively high water influx rate (0.07 ml d−1) for its low rate of energy turnover, and suggest that a significant proportion of this water was sourced from fog. Active body temperatures varied between summer (32.7 ± 2.4 °C) and autumn (34.4 ± 2.5 °C), but in both seasons R. bradfieldi maintained high and stable body temperatures while active. Our study supports the idea that a minimal energy requirement could be widespread within Rhoptropus geckos.