Bird sunning, also known as sunbathing or basking, is a widespread and natural behavior observed in many bird species. This activity involves birds deliberately exposing themselves to direct sunlight. It is a common part of their routine, contributing to their overall well-being.
Understanding Bird Sunning Behavior
Birds exhibit distinct postures when sunning, often choosing open, sunny locations for this activity. A common stance involves spreading their wings wide, sometimes drooping them to the side or fully outstretched, and tilting their heads. Some birds may lie prostrate on the ground, fluffing their body feathers, or even lie on one side with a wing extended like a flag.
This behavior can appear unusual to an observer, with birds sometimes appearing motionless or even panting if the temperature is high. Turkey vultures, for instance, are known to perch with their backs to the sun and wings spread to maximize exposure. Small songbirds might lie flat with ruffled feathers, while some species like pigeons and doves may lie down, lifting or spreading one wing at a time.
The Biological Reasons for Sunning
Sunning serves several important biological purposes for birds, contributing to their health and maintenance. One significant benefit is Vitamin D synthesis, which is similar to how humans produce this vitamin. When birds are exposed to ultraviolet B (UVB) rays from sunlight, a precursor molecule in their skin converts into Vitamin D3. This Vitamin D3 is then transported throughout the body, where it aids in calcium absorption, which is necessary for strong bones and beaks, and supports immune system function.
Feather maintenance is another reason birds sun themselves. The sun’s warmth can help dry feathers and make the oils from their preen gland less viscous, allowing them to spread more easily across the plumage during preening. Preening aligns barbules and keeps feathers in optimal condition for insulation, waterproofing, and flight.
Sunning also plays a role in parasite control. The heat from the sun can dislodge or kill ectoparasites like mites and lice on feathers and skin. Exposure to direct sunlight can create an inhospitable microclimate for these pests, or cause them to move to more exposed areas where birds can more easily preen them off. Studies have shown that temperatures reached during sunning can be lethal to feather lice.
Beyond these functions, sunning can assist with thermoregulation. By exposing their bodies to solar radiation, birds can passively warm themselves, supplementing their metabolic heat and conserving energy. They use morning sunning to warm their muscles for flight.
Distinguishing Normal Sunning from Distress
Observing a bird sunning can sometimes lead to concern, as their postures might resemble signs of distress or illness. However, normal sunning is a voluntary and healthy behavior. A sunning bird typically maintains alert eyes and a deliberate posture, and will usually be able to fly away quickly if disturbed.
Conversely, a bird in genuine distress or exhibiting illness will show different signs. These can include lethargy, an inability to move or fly away, continuously drooping wings, or labored breathing, sometimes indicated by a bobbing tail. Other indicators of illness might involve fluffed feathers that remain puffed up throughout the day, discharge from eyes or beak, or changes in feather quality like bald spots or dullness. While a sunning bird might pant with its mouth open to regulate its temperature, a truly sick bird’s open-mouth breathing would be accompanied by other signs of weakness.