Heera has lustrous, long black hair and wears a golden stud in her nose. She dresses in colourful saris and paints her fingernails. But Heera is not a woman. Nor is she a man. She is a hijra.

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Hijras - generally known in the west as hermaphrodites or eunuchs - have been part of the South Asian landscape for thousands of years. Marked out because of their sexual difference, they are a despised and neglected minority, lower even than untouchables.

But even though they generally provoke horror or ridicule, they have traditionally had a role to play on the margins of society as entertainers and as bestowers of curses and blessings. People who are building a new house sometimes hire them to dance in each new room, to take away any potential bad luck. They are also hired to dance at weddings and to celebrate the arrival of new-born babies.

Hijras are still considered an essential part of many religious rites

Heera and other hijras in Bangladesh still perform such roles. We first met her while she was dancing at a religious ceremony in honour of the sun god, a function organised by a lowly caste of Hindu shoemakers, where she had been hired to provide entertainment. But the everyday life of Bangladeshi hijras is far from being a laughing matter. With the spread of modern forms of entertainment --particularly TV-- the call for hijras is drying up. Increasingly, hijras are compelled to earn their livings by collecting money from shopkeepers --a form of mild extortion -- and by prostitution.

Hijras face prejudice and discrimination at every turn. Marked out by their sexual difference, they are hounded out of schools, and hence lack the necessary qualifications to get proper jobs. Its almost impossible for them to vote, to get a passport, or even to open a bank account.

Heera lives with an extended 'family', including children she cares for

Ostracized by normal society, hijras inhabit a secret society of their own. They live in small tight-knit groups, each led by a guru, or teacher. Most new hijras are inducted into the community by a guru when they reach puberty. A minority of hijras are born as hermaphrodites. But, we discovered during our research for Crossing Continents, many of them are males who undergo ritual castration at puberty. Publicly the hijras deny that castration takes place. In private, many allege that - although strongly attracted by hijra culture from an early age - they were castrated against their will.

Monu is the chief guru of all the hijras in Dhaka. She says she was castrated thirty years ago, although some hijras claim their leader reluctantly underwent the operation far more recently. The practice of castration used to take place only in India, a country which Monu and other Bangladeshi hijras visit regularly. More recently, castration is reported to have taken place in Bangladesh itself, near where Monu has her headquarters. It is alleged that castrations are necessary to keep up hijra numbers.

It's a murky world, about which very little is known, even how many hijras there are. One thing is certain, though. Whether born as hermaphrodites or castrated at puberty, hijras have a strong sense of their own separate identity. Heera says that when she is out in society, she thinks of herself as both male and female. At home, she thinks of herself as entirely female. She claims to have no sex life, but she loves children, and has recently adopted the child of her deceased sister-in-law. Unlike many hijras, Heera stays closely in touch with her biological family. And like many poor Bangladeshis, she hopes her adopted daughter can become either a doctor or an engineer.

Moves to rid hijras of the social stigma they carry and win more rights for the hijra community are still in their infancy in Bangladesh. Across the border in India, the movement is more advanced. There, hijras have started to demand recognition as a separate group deserving equal opportunities in education, jobs and housing. Earlier this year, India elected its first ever hijra MP. In a world where nepotism and corruption are rife, the hijra's lack of family connections has started to be seen as a political bonus.

Are there better times ahead for hijras across South Asia?

One Bangladeshi MP has suggested that hijras be given special voting rights. But most hijras themselves appear to believe that the most urgent need is to be officially recognised as full human beings, with the same rights to protection, jobs and welfare as other minorities. They may be different, but they are proud to be hijras - not lesser beings than ordinary men and women, but a mixture of both - members of the Third Sex.

Also in this edition of Crossing Continents: we speak to some other Bangladeshis breaking gender barriers - the women who're joining the country's armed forces for the first time. And we go twitching with one of Bangladesh's most devoted birdwatchers.