On an Indian grassland, a herd of blackbucks can look almost as though two different animals have gathered in the same place.
The females move through the grass in shades of pale brown and fawn. Young males look much the same. Then, one male begins to change. The colour around his neck and shoulders deepens. Dark streaks appear along his sides. His back grows darker, until the animal that once blended into the grass develops the unmistakable black-and-white coat that gives the species its name.
He was not born black.
This transformation is one of the most striking examples of sexual dimorphism in India’s wildlife — physical differences that develop between males and females of the same species. In the blackbuck (Antilope cervicapra), males gradually develop a dark brown to black upper coat as they mature, while females retain their fawn colouring.
So, what happens beneath that changing coat?
The black comes with growing up
A blackbuck fawn begins life with a light, yellowish-fawn coat. For much of its early life, a young male may look little different from a female.
A 2009 study conducted at Mahendra Chaudhary Zoological Park in Chhatbir observed fawns and documented changes in their coat colour. Researchers found that the transition in males was gradual. Darker hair first appeared around the neck and shoulders before spreading across the back and along the darker streaks on the sides.
The study reported that young males began developing their darker coat at around three years of age.
This timing is significant because it coincides with the animal’s transition towards sexual maturity.
The black coat is therefore not simply a colour that appears with age. It is one of several physical traits that distinguish a mature male from a young one, alongside his larger body and distinctive spiralling horns.
It is not just about appearance
This is where the term sexual dimorphism becomes useful.
Adult male blackbucks are dark brown or black across the back, neck, sides and outer parts of the legs. Their chest, abdomen, rump and inner legs remain white, as do distinctive areas around the eyes. Females, by contrast, are generally fawn or yellowish-brown where males are dark.
The result is one of India’s most recognisable wildlife patterns: a dark upper body sharply contrasting with white underparts.
But the difference goes beyond appearance.
Female blackbucks generally remain fawn-coloured — a shade that blends more closely with the dry grasslands and scrub habitats where the species lives. Photograph: (Bernard Dupont)
Blackbuck reproduction involves territorial males, competition and courtship. Research into the species’ reproductive behaviour has documented clear differences between male and female behaviour. Studies of male dominance have also found links between testosterone levels, aggressive behaviour, scent marking and social status.
The dark coat is therefore understood as part of a broader set of maturity-related traits. As males mature, changes in their reproductive physiology are accompanied by visible changes in their appearance.
Then come the horns
Place an adult male beside a female, and the difference becomes even more striking.
The male has long, ringed horns that twist into several spirals. Females generally lack these prominent horns.
The horns are not merely ornamental. Males use them during displays and confrontations with rivals, particularly when establishing or defending social and territorial status.
The coat and horns are therefore part of a larger transformation: a young male growing into an adult capable of competing with other males and taking part in reproduction.
Research on blackbuck social behaviour has found that dominant males show higher levels of aggression and scent marking, along with higher faecal testosterone levels, than subordinate males.
The black coat does not tell the whole story. It works alongside the horns, posture and behaviour in a set of traits shaped by reproduction.
Why do females stay brown?
There is another side to this story.
Female blackbucks generally remain fawn-coloured — a shade that blends more closely with the dry grasslands and scrub habitats where the species lives. Young blackbucks also begin life with this lighter colouring.
The species has recovered from severe declines caused by hunting and habitat loss. Photograph: (Raja Purohit)
Being less conspicuous can be important for animals living in open landscapes, particularly females with young. The difference between male and female coats also shows that evolution does not produce one universally “best” colour. Males and females can face different pressures.
The male’s dark coat is conspicuous. The female’s lighter coat is comparatively understated.
Both are traits shaped by life in the same landscape.
The black can change again
Even an adult male does not necessarily r emain the same shade throughout the year.
The Chhatbir study noted that blackbuck coats can fade somewhat during summer and regain a darker, more lustrous appearance after the rains. Historical field observations have also recorded seasonal changes in the intensity of the male’s dark coat.
So, despite its name, the blackbuck is not permanently or uniformly black.
It begins life fawn. It darkens as it matures. And its coat can change with the seasons.
A colour change tied to the grassland
There is one more reason this transformation matters.
Blackbucks depend on open landscapes, including grasslands, scrub and lightly wooded areas. These habitats support grazing animals, birds and predators, as well as communities that depend on them.
The blackbuck is among the most recognisable animals of India’s grasslands. It is protected under Schedule I of the Wildlife (Protection) Act, while the IUCN currently lists the species as Least Concern globally.
The species has recovered from severe declines caused by hunting and habitat loss. But its continued survival still depends on the open habitats where blackbucks can feed, breed and move.
And perhaps that is what makes the changing coat so fascinating.
The blackbuck we see racing across an Indian grassland did not start out black. That striking coat is something the animal grows into — along with its horns, its social role and its place in the herd.
