Field metabolic rates of giant pandas reveal energetic adaptations

Abstract

Knowledge of energy expenditure informs conservation managers for long term plans for endangered species health and habitat suitability. We measured field metabolic rate (FMR) of free-roaming giant pandas in large enclosures in a nature reserve using the doubly labeled water method. Giant pandas in zoo like enclosures had a similar FMR (14,182 kJ/day) to giant pandas in larger field enclosures (13,280 kJ/day). In winter, giant pandas raised their metabolic rates when living at - 2.4 °C (36,108 kJ/day) indicating that they were below their thermal neutral zone. The lower critical temperature for thermoregulation was about 8.0 °C and the upper critical temperature was about 28 °C. Giant panda FMRs were somewhat lower than active metabolic rates of sloth bears, lower than FMRs of grizzly bears and polar bears and 69 and 81% of predicted values based on a regression of FMR versus body mass of mammals. That is probably due to their lower levels of activity since other bears actively forage for food over a larger home range and pandas often sit in a patch of bamboo and eat bamboo for hours at a time. The low metabolic rates of giant pandas in summer, their inability to acquire fat stores to hibernate in winter, and their ability to raise their metabolic rate to thermoregulate in winter are energetic adaptations related to eating a diet composed almost exclusively of bamboo. Differences in FMR of giant pandas between our study and previous studies (one similar and one lower) appear to be due to differences in activity of the giant pandas in those studies.

Figure 1

Injecting DLW into one of the female release giant pandas in winter at Daxiangling Nature Reserve, Sichuan Province, China. Pandas were awake and alert during injections and blood sampling and voluntarily offered their forelimb for sampling. Photo by Wenlei Bi.

Figure 2

Relationship of field metabolic rates (FMR) of giant pandas measured with DLW to mass (a) and ambient temperature (b). We did the experiments at Research Base of Giant Panda Breeding in Chengdu, Sichuan Province, China (PB), at the Panda Valley facility of Panda Base in Dujiangyan, Sichuan Province, China (PV) and at the Daxiangling Nature Reserve, Sichuan Province, China (DXL). Elevated FMR of two pandas at DXL occurred at low ambient temperature as seen in 2b.

Figure 3

The thermal neutral zone of the giant panda as determined from field metabolic rates (FMR) measured in this study and resting metabolic rates (RMR) and FMR measured by Fei. et al.. The lower critical temperature is 8 °C and the upper critical temperatrure is 28 °C. The horizontal red line represents the predicted thermal neutral zone of the giant panda (see arrows). Field metabolic rates only give an approximate indication of the thermal neutral zone because the giant pandas are active and not resting.

Figure 4

Relationship of metabolic rate and body mass in giant pandas and other bears. Metabolic rate includes field metabolic rate (FMR), resting metabolic rate (RMR), and active metabolic rate. The orange regression line for RMR of large mammals was calculated using the data in Table 3 and included the resting metabolic rates of 20 large mammals from Sieg et al. and average resting metabolic rates of grizzly bears and polar bears from Pagano et al., sloth bears from McNab, and black bears from Toien. It did not include the RMR of the giant panda. The regression equation is (RMR) = 106.41 (mass_kg) + 671.77 (r² = 0.524, p = 0.00), where y is RMR and x is body mass. The green dashed line is the regression line from Nagy et al. (FMR = 4.82 (mass_g)^0.73). The blue regression line for FMR of large mammals included the FMR of 10 large mammals and active metabolic rates and FMR of bears from the Table 4. It did not include the FMR of giant pandas. The regression equation is (FMR) = 292.66 (mass_kg) + 585.35 (r² = 0.99, p = 0.00) where y is FMR and x is body mass.