Birds from Whanganui's Bushy Park in fundraising sperm race

Healthy hihi sperm is pretty precious in New Zealand, and an international competition betting on their vigour is set to help the endangered species.

There are so few hihi (stitchbirds) left that inbreeding has happened, making the males less fertile. They have to compete to mate with females, and lots of healthy chicks are needed to keep the species going.

People can now make $10 bets on which of 128 male hihi has the fastest sperm. The birds are from four of the seven remaining populations of the birds, one of them at Whanganui's Bushy Park Sanctuary.

Betting takes place online at www.hihispermrace.nz until April 22. The winner will be the bird that Otago University's Dr Helen Taylor finds has the fastest sperm.

There are big prizes to be won. They include family passes to three sanctuaries with hihi, cases of wine, T-shirts and a set of native bird cards with images produced by Whanganui's Merilyn Payne.

Money from the bets will be used to maintain existing hihi populations, and create new ones.

That's not so easy, because the nectar-loving birds need complex, mature, predator-free forest to live in.

But Dr Taylor said hihi used to be widespread in the North Island and keeping them is worthwhile.

"They're cheeky little birds with a tonne of personality. We'd like them to be a bit more loved by the public."

The competition idea began with a campfire conversation after a day of fieldwork. Dr Taylor and her colleagues joked about betting on which bird had the fastest sperm.

They extended that to the public and The Great Hihi Sperm Race was born.