An ephemeral metropolis for birds
For much of the year, the Great Rann of Kutch is a 26,000-square-kilometer salt-encrusted desert. Temperatures can reach 50°C (122°F) in the summer and drop below freezing in the winter. Then, the southwest monsoon arrives between June and September. A combination of rainwater and tidal surges from the Arabian Sea floods the flats to a depth of about 50 cm, transforming the landscape into a shallow, saline wetland.
This inundation triggers a bloom of life. The brackish water supports algae, brine shrimp, and other small organisms that are the primary food for flamingos. This temporary abundance attracts two species of flamingo: the Greater Flamingo (Phoenicopterus roseus) and the smaller, more numerous Lesser Flamingo (Phoeniconaias minor). The Rann of Kutch is the only known breeding site in Asia for both species. The area within the Kutch Desert Wildlife Sanctuary where the birds congregate is known as "Flamingo City," a name given for the immense colonies that form there. In 1945, ornithologist Dr. Sálim Ali estimated a population of half a million birds at the site. More recent surveys have observed congregations of around 100,000 Lesser Flamingos and 10,000 Greater Flamingos exhibiting courtship behavior.
To cope with the extreme salinity of their environment, flamingos have specialized supraorbital glands near their eyes. These glands function as a biological desalination system, filtering excess salt from their blood which is then excreted through their nostrils.
Architecture of a temporary city
Successful breeding is entirely dependent on the timing and extent of the monsoon flooding. If conditions are right, the birds begin constructing their nests. Using their beaks, both partners build a conical mound from the sticky mud of the salt flats. These nests stand one to two feet high, an elevation to protect the single egg from rising floodwaters. The female lays one egg, and both parents take turns incubating it for about 27 to 30 days.
After hatching, the grey-downed chicks leave the nest within four to eight days. They gather in immense groups called crèches, which can contain thousands of young birds supervised by a few adults. This allows the majority of the adult flamingos to forage for food, sometimes traveling up to 100 kilometers away, before returning to feed their specific chick. The parents feed the chicks a nutrient-rich "crop milk," a reddish secretion produced in their upper digestive tracts. The pink and reddish colors of adult flamingos come from beta-carotene pigments present in the algae and crustaceans they consume. Without this diet, the birds' feathers would be white or grey. As the long dry season returns and the water evaporates, the flamingos and their now-fledged young depart, leaving the salt flats to bake under the sun until the next monsoon.