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Why does the head and heart warm first when an Arctic ground squirrel awakens?

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The image shows a group of Virginia big-eared bats sleeping upside down in a dark cavern. — Dormancy Virginia big-eared bats (*Corynorhinus townsendii virginianushibernating*) are true hibernators, entering a state close to death for much of the winter.

When an Arctic ground squirrel awakens from hibernation, the head and heart warm first due to a process called differential vasodilatation, which involves the widening of blood vessels in the anterior (front) part of the body.1

By concentrating circulation in the head and heart region, the animal is able to maintain high blood pressure, which is essential for efficient and rapid warming. This localized blood flow is a vital adaptation; if the blood vessels were to dilate throughout the entire body simultaneously, the heart would be unable to maintain the necessary blood pressure to support the arousal process, even if the heart rate were to double. Once the anterior portion of the body has been sufficiently warmed, the posterior (rear) part of the animal warms rapidly to complete the transition to full activity.1