Bhubaneswar, July 28: Two black tigers, born at the Nandankanan Zoological Park on July 28 last year, were today put on public display in an enclosure in the zoo.

Four cubs, including the melanistic duo, were born to a four-and-a-half-year-old white tigress, Sneha, and her partner, Manish, an eight-year-old Royal Bengal tiger, in an off-exhibit enclosure in the zoo last year. The other two cubs were also brought to the public enclosure today.

The word "melanism" is deduced from Greek, and it means black pigment.

While one of the melanistic tigers has yellow and black stripes covering around 50 per cent area of its body, the other has prominent black stripes on a white coat.

Principal chief conservator of forest (wildlife) S.S. Srivastava said Nandankanan was the first zoo in the country to have melanistic tigers born in captivity. "It is a rare phenomenon. Earlier, a melanistic tiger had been spotted in the wilds of Similipal," said Srivastava.

A forest department official said black tiger was a rare colour variant often resulting from inbreeding. "The black colour is due to pseudo-melanism in which the dark pigment melanin is developed in the skin," he said.

In June 2013, a rare melanistic or black tiger had been photographed in the core area of the Similipal National Park in Mayurbhanj district.

As soon as the melanistic tigers made their entry to the public enclosure, visitors vied with each other to have a glimpse of them. "We have been eagerly waiting to see the melanistic tigers. It's a unique experience. They are very different from the white and other normal tigers. This would be a major attraction for the people visiting the zoo," said Abhisek Jena, a visitor from Khurda.

Though the zoo celebrates the birthday of tiger cubs every year with schoolchildren, the Nandankanan authorities have decided to observe the birthday of the four cubs in a simple manner because of the death of former President A.P.J. Abdul Kalam.

Experts believe that among tigers of other colours, only white tigers are discussed in detail. "However, there are at least 14 known types of body colouration found in tigers. The appearance of tigers with aberrant colouration is an extremely rare natural phenomenon. Only in populations where inbreeding has a longer and stronger influence, the appearance of aberrants would be more frequent," said former research officer of the state forest department and a tiger expert Lala A.K. Singh.