Which of the following is a characteristic of both mammals and birds?

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Accepted Answer

1) Definition: Being "warm-blooded" (endothermy/homeothermy) means an animal generates and retains metabolic heat to maintain a relatively constant internal body temperature independent of immediate ambient conditions.

2) Physiological basis: Both groups produce metabolic heat at high rates, possess insulating coverings (fur in mammals, feathers in birds) that reduce heat loss, and have circulatory and respiratory adaptations (efficient lungs, high metabolic blood flow, four-chambered hearts) that support sustained internal heat production.

3) Thermoregulatory mechanisms: Members of these groups use physiological responses such as shivering thermogenesis, vasoconstriction/vasodilation, and behavioral adjustments to keep body temperature stable.

4) Typical body temperatures: Most mammals maintain internal temperatures near $37^\circ\mathrm{C}$ while many birds keep slightly higher averages around $40^\circ\mathrm{C}$, illustrating consistent internal regulation across both classes.

5) Functional outcome: These shared traits allow both mammals and birds to remain active in a wide range of environments and to sustain high levels of activity and metabolic function.

FINAL_ANSWER: D

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