The most important factor in thermoregulation is evaporative heat loss. As birds have no sweat glands, they cannot lose heat as mammals do by sweating through pores. Many of the physical and behavioral adaptations to minimize heat stress involve increasing or decreasing the surface available for the evaporation of water from legs, feet, bills, and skin. Most seabirds, and other birds that experience intense solar radiation, use gular flutter to lose heat. Seabirds may also lose heat by evaporation in flight or by entering water to give off heat through their legs and feet, although their tolerance towards hyperthermia allows birds to spend more time protecting their nests before they need to leave to find water for evaporative cooling.
Water plays a crucial role in heat loss for seabirds.
Seabirds are different from other birds in that they have a nasal gland that concentrates the salt they absorb when drinking sea water, allowing them to drink sea water and use the desalinated water internally in evaporative cooling. To help picture this, imagine a sphere. For this reason, smaller birds need to replace lost heat at a greater rate than larger birds to maintain the same Tb. Smaller birds, therefore, require more food for energy per each gram of mass. Data taken during Christmas counts revealed species of birds, thought to be too small to survive in northern regions, present wherever larger birds were observed.