It’s a fair question: How do arctic wolves not get cold-related injuries to their paws as they endure harsh winters on Ellesmere Island or in northern Canada?

The simple answer, according to biologists, is that instead of blood flow being reduced to their feet in the cold temperatures, the opposite occurs. Blood flow in fact increases to their feet.

This is one key adaptation that allows arctic wolves to thrive in their frigid environment.

The details

In this 1973 paper, researchers Kenneth Swan and Robert Henshaw write that “the foot of the adult arctic wolf has been observed to tolerate exposure to extreme cold (-30° Celsius [-22 F]) for many hours without apparently cold injury.

“The foot pads of the wolf, standing on ice-covered tundra, subjected to high winds, are exposed to temperatures well below freezing (-30° C) for sustained periods of time. Without the adaptive facility to maintain foot temperature near 0° C, irreversible cold injury would transpire rapidly.”

Swan and Henshaw considered that in men not acclimatized to cold, exposure to the cold results in vasoconstriction (or a narrowing of the blood vessels and a reduction of blood flow). That vasoconstriction causes cold injury.

For men acclimatized to the cold, there is a vasodilation, or dilation of blood vessels.

They applied those principles to the arctic wolf.

“While direct evidence of cutaneous vasodilation in response to cold is lacking in the arctic wolf, indirect evidence lends support to this being the only possible mechanism for supplying heat to the cold exposed extremity. Blood volume in the extremity does not decrease but rather actually increases in cold exposed feet.”

As part of their study, Swan and Henshaw dipped the left foot of a sedated arctic wolf into a hyper-chilled bath of ethylene glycol, ethyl alcohol and water. Dry ice was added to maintain a temperature of -30° C. Using a series of thermometers, the biologists studied the results of the cooling bath.

In summary, they wrote: “This cold adapted species protects its cold-exposed extremity with an augmented heat input to maintain the most superficial tissues at a temperature level just above freezing. This delicate balance prevents injury while simultaneously minimizing heat loss.”

Earlier findings

In this paper published one year earlier, Henshaw, Larry Underwood and Timothy Casey did a similar experiment with a cold water bath (cooled to a chilly -38° C). They found that when they applied a tourniquet at mid-thigh, there was a “rapid drop in pad temperature of the immersed foot. Pad temperature rose even more rapidly when the tourniquet was released.”

This finding lends more credibility to the belief that blood flow plays a key role in keep those feet from freezing.

Another key finding from this experiment was that foot temperature was “thermally independent” of the wolf’s central temperature.

They wrote: “Because body core temperature fell throughout these experiments, temperature of the blood entering the leg … also dropped. Despite this varying heat content of the blood, foot pad temperature was maintained constant.”

As they summarized their findings, Henshaw, Underwood and Casey wrote: “The ability of these cold-acclimatized wolves … to maintain their feet in excess of 35° C above the bath temperature must be accounted for in increased blood-borne heat input to the foot pads. …

“No freezing of tissues has been reported in animals living in the arctic. A dynamic balance must be struck between heat loss to the environment and heat input from the body core. Regulation of heat balance in the foot pads of arctic-adapted terrestrial species therefore would be prime adaptive significance.”