Foreleg Licking Cools Skin

close up of a kangaroo licking its foreleg making the fur wet against a blurry background

Biological Strategy

Red kangaroo

AskNature Team

Image: Brent Weichsel / Flickr / Some rights reserved

Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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Protect From Temperature

Many living systems function best within specific temperature ranges. Temperatures higher or lower than that range can negatively impact a living system’s physiological or chemical processes, and damage its exterior or interior. Living systems must manage high or low temperatures using minimal energy, which often requires controlling responses along incremental temperature changes. To do so, living systems use a variety of strategies, such as avoiding high or low temperatures, removing excess heat, and holding heat in. Insulation is a well-known example of managing low temperatures by retaining heat using thick layers of hair, fur, or feathers to hold warm air next to the skin.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Forelegs of red kangaroos facilitate evaporative heat loss by having a special anastomosing network of superficial vessels cooled by licking.

“Cutaneous evaporation includes water loss through the skin (passive diffusion and sweating) and water spread onto the skin (licking)…Kangaroos and some wallabies have a special anastomosing network of superficial vessels in their forelegs to facilitate heat loss via licking (Needham et al. 1974), and this is most developed in M. [Macropus] rufus (Needham 1982). Large increases in foreleg blood flow occur in M. rufus when Ta [air temperature] is raised above thermoneutral levels (Needham et al. 1974; Needham and Dawson 1984). While circumstantial, the data suggest that licking provides most of the nonrespiratory EHL [evaporative heat loss] of M. rufus at 45°C.” (Dawson et al. 2000:380)

Last Updated October 23, 2016

References

“Red kangaroos have excellent thermoregulatory abilities: evaporative heat loss mechanisms such as panting, sweating, and licking (Dawson 1973, 1989; Dawson et al. 1974; Needham et al. 1974) enable them to cope with high externally (Dawson 1972) and internally produced (Kram and Dawson 1998) heat loads. While the evaporative heat loss mechanisms utilised by red kangaroos have been suggested to follow an efficient pattern, we do not know the relative contribution of these mechanisms at high environmental temperatures. In regard to the grey kangaroos, little has been reported except that they pant and lick. Licking has been suggested to be the grey kangaroo’s major route of evaporative heat loss (EHL) at high temperatures (Robertson and Morrison 1957).” (Dawson et al. 2000:374)
“Cutaneous evaporation includes water loss through the skin (passive diffusion and sweating) and water spread onto the skin (licking)…Kangaroos and some wallabies have a special anastomosing network of superficial vessels in their forelegs to facilitate heat loss via licking (Needham et al. 1974), and this is most developed in M. [Macropus] rufus (Needham 1982). Large increases in foreleg blood flow occur in M. rufus when Ta [air temperature] is raised above thermoneutral levels (Needham et al. 1974; Needham and Dawson 1984). While circumstantial, the data suggest that licking provides most of the nonrespiratory EHL [evaporative heat loss] of M. rufus at 45°C.” (Dawson et al. 2000:380)

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