Some Arctic birds, particularly gulls, are forced to spend hours standing on cold ice floes – and unlike snowy owls and ptarmigans, they have bare feet, uninsulated by feathers. However, these birds do have a mechanism in their legs which prevents large quantities of body heat from being lost through their feet.

The blood vessels in a bird's leg are located next to each other, so that heat can pass from arteries to veins. Warm blood flows from the bird's heart to its feet via the leg arteries. As the blood travels towards the feet, heat from these arteries warms the blood in neighbouring veins, which are carrying cold blood from the feet back towards the heart. The heat is thus returned directly to the heart without being lost out on the ice, and the "pre-warmed" blood from the veins does not chill the bird when it re-enters its body core. The blood going out to the feet is pre-chilled, with the result that the gull has continuously cold toes. However, this is preferable to having the whole body lose heat. This mechanism, which is also used by long-legged caribou, is called counter-current heat exchange, and functions to keep as much heat as possible inside the bird's body.

A second mechanism also helps to keep the gull's warmth inside its body, by constricting arteries and reducing the flow of blood to the feet. By reducing the amount of blood travelling to its bare feet, the bird loses less energy to the surrounding environment. The combination of this adaptation and the countercurrent mechanism mean that a bird's body can be perfectly warm while its feet are as much as 30ºC colder than its core! This would be the equivalent of a human being having feet about the same temperature as milk in the fridge.