Black Winged Stilt (Himantopus himantopus)
The Black winged stilt, Himantopus himantopus is a widely distributed wading bird with long legs. It has been reported from Asia, Africa, Australia, Europe, North America, South America and the Indian sub continent except the Andaman and Nocobar Islands. It inhabits the borders of open wetlands, coastal pools, mud flats, marshy grasslands, village tanks, salt pans and tidal flats. The bird is about 33 to 43 cms tall with a 68 cms wing span and tall legs (24 cms) which allow it to wade in comparatively deep waters. The bird has been reported to have the longest legs relative to its body size within any living birds. The plumage is over all white with black glossy wings. The under parts are white. The color of the neck and head varies from black to all white. Females tend to have less black on head and neck all year round while males have more black in summers. Males usually get all white heads in winter. This specimen from the out skirts of Bharatpur in Rajasthan, India exhibits a grayish black neck and skull region. The bill is long pointed and blackish. Generally a weak flier, it is a good swimmer also.
The diet is mainly composed of aquatic invertebrates, fish, crustaceans, aquatic and terrestrial insects, molluscs and spiders, oligochaete and polychaete worms and amplibians.
In colder regions the breeding season is during summers and in the tropics it may start with rains.
It is a species of least concern as notified by the IUCN.
It is often of interest to know why birds stand on one leg. Standing on one leg is the most efficient and stable stance for long legged birds. It demands less energy than standing on both legs. As one of the legs is raised, it locks the other leg in position and the bird is totally balanced. It is less tiring for a bird to stand on one leg. Standing on one leg also provides camouflage against predators who may mistake a single leg as a stem of a reed. A one legged stance also allows the bird to rotate round with greater ease.
The loss of body heat is more in water than in air and in the case of a bird standing in water on both legs this heat loss is almost twice that as from one leg. A one legged stance also helps to regulate the body temperature. The legs are the only part of body without feathers and from which heat can escape in winters. A tucked in leg provides lesser loss of body heat and greater warmth. Birds may generally stand on one leg during the winter and on both legs during the summer months unless the necessity of camouflage or injury forces them to use only one leg. Generally birds species that can stand on one leg are more successful.
Acknowledgements-Dr. Yashpal Singh, Mrs. Neena Singh, Mr. Rajesh Bedi, Manoj Kumar Yadav