When maintaining a body temperature warmer than that of the environment heat loss is to be expected (Thomas, Fordyce 2007). Penguins reduce the amount of heat loss by using methods such as subcutaneous fat and effective insulation from dense plumage (e.g. Adélie penguins have approximately 100 feathers per square inch) combined with other methods of reducing heat loss (Thomas, Fordyce 2007).
Adélie Penguins have dense plumage, this is formed from two layers of feathers (Fig 9), the bottom layer is an insulating down which maintains body heat the uppermost feathers are contour feathers which provide waterproofing and streamlining abilities these are short lanced and overlap (Dawson et al. 1999). Penguins also have a unique feature to birds in that their feathers cover their body in an even layer, even covering their bill to keep in as much heat as possible (Dawson et al. 1999). These two layers of feathers (Fig 9) trap air so as to insulate penguins from the cold of the Antarctic air whilst providing a waterproof layer for diving (Du et al. 2007). During diving penguins can’t allow their feathers to trap too much air otherwise they would become positively buoyant, which would hinder their diving ability (Kooyman et al. 1976).
This insulating layer is further hindered with diving as the pressure of diving pushes the air out of the feathers therefore nullifying any insulating effect in the water (Wilson et al. 1992). This is counteracted by penguins having muscles that will lock down the feathers, removing any bubbles of air and providing a waterproof barrier (Kooyman et al. 1976). This combination of hydrostatic pressure and specific muscle action working to reduce the air insulating layer, allows for neutral or negative buoyancy when swimming hunting (Wilson et al. 1992). Care is also taken when moulting, old feathers do not begin to be lost until the new set are in place.
Like other Antarctic species, penguins use both subcutaneous fat and a counter current heat exchange system to maintain body temperature in cold conditions (Campbell, Norman 1998). The subcutaneous fat in penguins proves to be an effective insulator, in studies it has been shown that subcutaneous fat provides much of the insulation for penguins (approximately one fifth of total heat insulation)(Drent, Stonehouse 1971) . This layer of sub-dermal fat is therefore an important part of the penguins insulation (Drent, Stonehouse 1971) . However if the layer is too thick it can mean higher energy cost of swimming (Drent, Stonehouse 1971) which is undesirable and therefore presents the need for more than one method of insulation.
Surface area is another important adaptation for cold environments that can be overlooked (Thomas, Ksepka & Fordyce 2011). Penguins are the smallest of the homeotherms, however when compared with other marine birds they are generally much larger (Drent, Stonehouse 1971). Therefore due to their large size have a low surface area to volume ratio (Drent, Stonehouse 1971). Their smaller surface area to volume ratio means that they have a reduced heat loss as there is less surface area overall from which to lose heat (Drent, Stonehouse 1971).
The counter current heat exchange (Fig 10) works by exchanging heat from blood leaving the body into limbs, such as fins and feet (particularly high in the feet), back into the blood entering the body which has been cooled by the environmental conditions (Thomas, Ksepka & Fordyce 2011). This helps to prevent heat loss from the extremities, by preventing heat in the blood being in close contact with the external environment (Thomas, Ksepka & Fordyce 2011).
Blood shunting is another helpful adaptation, this means that blood flow to an area with high heat loss can be reduced or even stopped from areas of high heat loss such as flippers and feet (Wilson, Adelung & Latorre 1998). Blood flow to flippers and feet can be changed by either increasing if penguins become too warm, or decreasing if heat loss is becoming too great (Wilson, Adelung & Latorre 1998). As mentioned above heat loss is minly from the feet, penguins (such as the Adélie penguin) counteract this by pressing their feet against their bodies when they are prone to keep them warm, or pressing digits together to reduce surface area can decrease heat loss (Wilson, Adelung & Latorre 1998, Stonehouse 1960).
In conclusion it appears that penguins are well adapted for the extreme environment of the Subantarctic and Antarctic regions with multiple adaptations to reduce heat loss shown above.