Technically this bird is a Eurasian spoonbill (Platalea leucorodia), but its one-legged stance somehow reminded me of a pirate. It stood in the shallow waters which spill through parts of the Rann of Kutch, looking for insects. It eats molluscs, fish, frogs and leeches too, but I don’t think that the briefly flooded desert would have any of these. Why did it stand one one leg? A study on flamingos (would that be a study on scarlet?) performed by two people in Pennsylvania in 2009 suggested that water birds raise one foot out of the water to keep from getting too cold. This was an easy thing to understand, and was reported in lots of newspapers and magazines. A year later another study, this time from New Zealand, on many kinds of waders, including flamingos and spoonbills, found that birds stand on one foot regardless of the temperature of the water. So they concluded that the reason for standing on one leg could not be to maintain their body temperature, and instead suggested an interesting different reason for this habit.
It was a winter afternoon, and it was quite warm in the desert. Most of the spoonbills that I saw were still and resting. Only a few strode around the shallows looking for food. Most of the drowsy birds stood on one leg. This reminded me of the suggestion by the New Zealanders. They put together two earlier observations. The first is one that found in 2009 that flamingo (and perhaps other waders) anatomy makes it easier for them to stand stably on one leg than on two, so much so that even dead birds can be more easily balanced on one leg. The second is a landmark study from 1999 which found that birds sleep with one half of their brain on! During this period of sleep, as the bird switches awareness from one hemisphere of their brain to another, they see from one eye, or the other. The New Zealanders observed that waders switch from one leg to another occasionally while sleeping, and suggested that when one hemisphere of the brain sleeps, the leg which is controlled by it is retracted out of the water to help the birds balance more easily while asleep. I find this a wonderfully economical explanation, which puts together two surprising facts about the anatomy and physiology of birds. The next time you see a bird standing on one leg, stop for a moment to check whether it could be half asleep.