Ursids are the largest mammals to retain a plantigrade posture. This primitive posture has been proposed to result in reduced locomotor speed and economy relative to digitigrade and unguligrade species, particularly at high speeds. Previous energetics research on polar bears () found locomotor costs were more than double predictions for similarly sized quadrupedal mammals, which could be a result of their plantigrade posture or due to adaptations to their Arctic marine existence. To evaluate whether polar bears are representative of terrestrial ursids or distinctly uneconomical walkers, this study measured the mass-specific metabolism, overall dynamic body acceleration, and gait kinematics of polar bears and grizzly bears () trained to rest and walk on a treadmill. At routine walking speeds, we found polar bears and grizzly bears exhibited similar costs of locomotion and gait kinematics, but differing measures of overall dynamic body acceleration. Minimum cost of transport while walking in the two species (2.21 J kg m) was comparable to predictions for similarly sized quadrupedal mammals, but these costs doubled (4.42 J kg m) at speeds ≥5.4 km h Similar to humans, another large plantigrade mammal, bears appear to exhibit a greater economy while moving at slow speeds.

Recent work suggests that moose ( Alces alces (L., 1758)) in the boreal ecoregion may be nutritionally limited by the availability of protein as a consequence of both low nitrogen (N) concentrations and high tannin levels in their principal foods. However, the ability of moose to digest protein in the presence of tannins is unknown. We undertook a series of digestion trials with captive moose to quantify the effects of tannins and compare the digestive capabilities of moose to other browsing cervids. We fed four moose 14 single-species diets including 10 native tannin-containing forages and 4 non-tanniferous foods over four winters. True protein digestibility in moose was 92%, and metabolic fecal N excretion was estimated at 0.389 g N/100 g dry matter (DM) intake. Tannins reduced protein digestion, on average, by 38%, and the rate of reduction in protein digestion was estimated to be 8.28 g protein/100 g DM per unit protein-precipitating capacity. The digestion of protein, neutral detergent fiber, DM, and energy of tanniferous foods was not significantly different between moose and mule ( Odocoileus hemionus (Rafinesque, 1817)) or white-tailed deer ( Odocoileus virginianus (Zimmermann, 1780)). However, our experiments provide refined assays for evaluating the nutritional quality of browses for moose.