Which group of organisms exhibits the highest metabolic rate?

Birds exhibit the highest metabolic rate among the groups listed. This elevated metabolic rate is primarily due to their need for efficient energy use during flight. Birds have highly developed respiratory systems with air sacs that allow for continuous airflow through their lungs, enhancing oxygen intake during both inhalation and exhalation. This anatomical feature supports their high energy demands for flight, which requires a significant amount of oxygen and energy.

Additionally, birds have a high body temperature, typically between 102°F and 107°F (39°C to 42°C), which is linked to their elevated metabolic activity. This adaptability to extreme energy demands is why many birds have a higher basal metabolic rate compared to reptiles, mammals, and amphibians, allowing them to sustain the physical exertion required for activities such as migration and foraging.