Why some birds roost in peg-legged stance ?

 

Its common to see some birds relaxing or sleeping on one leg. But why ? This simple question had always baffled me till I took to bird photography seriously and began to observe their behavior. I remember in childhood whenever I asked the elders that why birds, especially egrets  stand of one leg, pat would come the reply, “its prayer time”. During my recent visit to Siswan dam, I saw a large number of Ruddy Shelducks basking while standing on one leg. Now I know these species  understand  better why to relax on one leg. They seem to be aware that they have adaptations to manage heat loss.

We all know most of  the birds have naked legs without insulating feathers. Their feet being closer to environmental temperature, they don’t lose as much heat as they would if they were at body temperature. The widely known theory is that by standing on one leg, they conserve heat and prevent at least it from heat loss. A bird with its one foot tucked up reduces by half the amount of heat lost through its unfeathered  limbs. In other words, the arteries that transport blood into the legs of birds are in contact with the veins that return blood to their heart. The warm arteries heat the cooler veins which also cool the arteries. Also, during winter some species  flutter  their feathers to cover both legs. Interestingly, to get extra warmth, they tuck their beaks under their shoulder feathers, but not under their wings.

Ever thought what makes birds comfortable in this posture of standing on one leg for a long time. Birds don’t have muscles in their feet or legs. Each of their leg has two flexor tendons that run from shoulder to the toes. With change in angle of their ankle they are able to close and lock their feet around a perch. Therefore they are able to sleep while standing on one leg.