The relationship between mass and metabolic rate holds true across many species, and even follows a specific mathematical equation. Because of this, a smaller animal would need more energy and a higher metabolic rate to maintain a constant internal temperature (in an environment below its body temperature).
How does Fever increase metabolic rate?
A common pathological cause for a high BMR is fever, since a rise in body temperature increases the rate of cellular metabolic reactions. It is estimated that for every degree Fahrenheit of rise in body temperature, the BMR increases by 7 percent.
Do Endotherms have higher metabolic rate?
Endotherms use metabolic heat to keep a stable body temperature, while ectotherms do not. Among endotherms, smaller animals tend to have higher per-gram basal metabolic rates (a "hotter" metabolism) than larger animals. The same is true among ectotherms, though we can't compare between the groups.