Seasonal field metabolic rate and dietary intake in Arabian Babblers (Turdoides squamiceps) inhabiting extreme deserts

1. Arabian Babblers (Turdoides squamiceps Cretzsch.; mean adult body mass = 72.5 g) inhabit extreme deserts of Israel. They consume invertebrates and fruits and, at least at our study site, do not drink. It was hypothesized that babblers (1) in general, use relatively less energy and water than other birds of its body mass; and (2) consume a more water-rich diet (mainly fruits) in summer and more energy-rich diet (mainly invertebrates) in winter. Doubly labelled water was used to determine seasonal field metabolic rate (FMR) and water influx rate (WIR) and to estimate dietary selection in free-living Arabian Babblers. 2. Babblers in winter weighed significantly more than in summer, and males weighed more than females in both seasons. Tritiated water (TOH) space, as a proportion of body mass, was higher in males than in females in summer but no difference between sexes was found in winter. Males in summer had a higher TOH space, proportionally, than males in winter but there was no difference between seasons in females. Mass-specific WIR did not differ between sexes in any season and averaged 0.475 ml g(-1) d(-1) in winter which was significantly higher than the 0.283 ml g(-1) d(-1) in summer. 3. The mean daily energy expenditure of the babblers did not differ either between seasons or between sexes within seasons and averaged 1.61 kJ g(-1) d(-1) in winter and 1.68 kJ g(-1) d(-1) in summer. It was calculated that each babbler consumed an average of 5.09 g dry matter invertebrates and 1.83 g dry matter fruits in summer (for a 68.2-g bird; mean adult body mass in summer) and 3.49 g dry matter invertebrates and 6.61 g dry matter fruits in winter (for a 76.9-g bird; mean adult body mass in winter). 4. When compared with other avian species, FMR and WIR of babblers were lower than bird species in general, but were similar to those of other desert birds. It was calculated that proportional dietary intake, on a dry matter basis, included 0.79 insects and 0.21 fruits in summer and 0.35 insects and 0.65 fruits in winter. Therefore, the babblers consumed a relatively energy-rich diet in summer and water-rich diet in winter which refuted our hypothesis. Most of the metabolizable energy was provided by invertebrates in both seasons; invertebrates provided more water in summer but fruits provided more in winter.