From Backside postcard:
The Nilgai is the largest Asian Antelope. It is one of the most commonly seen, wild mammals of central and northern India, often seen in farmland or scrub forest. The mature male appears ox-like and is also known as the blue bull. Nilgai are diurnal and tend to form single-sex herds outside of the breeding season. Herds are not of fixed composition, with individuals joining and rejoining through the year. Female herds typically contain three to six adults, together with their calves, whereas bulls form herds of two to 18 individuals.
Zoological Survey of India