Soak up the sun: Understanding the Spread-winged stance
Turkey vultures (Cathartes aura), though unattractive, are quite a sight to behold when a flock all have their wings outstretched to their impressive length. This behavior is known as sunning; turkey vultures stand in a spread-winged stance to absorb the sun's radiation. Many birds are known to sun, each with a different purpose, such as drying wet feathers or forcing the removal of parasites. Turkey vultures' main reason for sunning is to raise their body temperature so they can have enough energy to go about their daily activities.
It is important to note that turkey vultures are one of few birds that intentionally put themselves into a daily hypothermic state each night, lowering their body temperature a few degrees. This has been thought to conserve energy since there is not a constant source of food (carrion) available. In a study on turkey vulture thermoregulation, completed by Zeev Arad, Uffe Midtgård and Marvin H. Bernstein, turkey vultures were found to have a thermoregulation system that allowed for the decrease in internal temperature. The study focused on the changing temperatures of the birds and the occurring behaviors, which included wing extensions.
By better understanding the physiological aspects of the turkey vulture, we can better comprehend the importance of sunning. Dr. Robert G. Clark and Robert D. Ohmart completed a study on the possible function(s) of the spread-winged posture seen in turkey vultures. Turkey vultures of a communal roost in Arizona were observed before and a few minutes after the sun rose each morning. The researchers found that the vultures, whether the night had been cold or warm, always participated in the act of sunning, as long as the sun was directly visible. They deduced that the vultures use the sun's intense rays to restore their body heat from hypothermic conditions so that they are able to fly and expend energy in finding their next meal.
The spread-winged stance of the turkey vulture can be seen through two different postures, proposed by Mike Mossman. The more efficient stance and the most recognizable is the extended posture in which the the wings are stretched to their full length and the vulture faces away from the sun, so that the dark feathers of its dorsal side can absorb heat. The delta posture has the turkey vulture in a more heart-shaped stance, with its body and head facing directly towards the sun. This allows the rays to be focused on the body; this stance is adopted less often than the extended.
It is important to note that turkey vultures are one of few birds that intentionally put themselves into a daily hypothermic state each night, lowering their body temperature a few degrees. This has been thought to conserve energy since there is not a constant source of food (carrion) available. In a study on turkey vulture thermoregulation, completed by Zeev Arad, Uffe Midtgård and Marvin H. Bernstein, turkey vultures were found to have a thermoregulation system that allowed for the decrease in internal temperature. The study focused on the changing temperatures of the birds and the occurring behaviors, which included wing extensions.
By better understanding the physiological aspects of the turkey vulture, we can better comprehend the importance of sunning. Dr. Robert G. Clark and Robert D. Ohmart completed a study on the possible function(s) of the spread-winged posture seen in turkey vultures. Turkey vultures of a communal roost in Arizona were observed before and a few minutes after the sun rose each morning. The researchers found that the vultures, whether the night had been cold or warm, always participated in the act of sunning, as long as the sun was directly visible. They deduced that the vultures use the sun's intense rays to restore their body heat from hypothermic conditions so that they are able to fly and expend energy in finding their next meal.
The spread-winged stance of the turkey vulture can be seen through two different postures, proposed by Mike Mossman. The more efficient stance and the most recognizable is the extended posture in which the the wings are stretched to their full length and the vulture faces away from the sun, so that the dark feathers of its dorsal side can absorb heat. The delta posture has the turkey vulture in a more heart-shaped stance, with its body and head facing directly towards the sun. This allows the rays to be focused on the body; this stance is adopted less often than the extended.
The extended posture. Click to enlarge.
The delta posture. Click to enlarge.
References
- Thermoregulation in Turkey Vultures. Vascular Anatomy, Arteriovenous Heat Exchange, and Behavior Zeev Arad, Uffe Midtgård and Marvin H. Bernstein, 1989 (Article linked in the first "study")
- Spread-Winged Posture of Turkey Vultures: Single or Multiple Function? Robert G. Clark and Robert D. Ohmart, 1985 (Article linked in the second "study")
- Spread-wing Posturing in the Turkey Vulture Mike Mossman, 1974 (Article linked in "postures")
