Mammalian fertilization

fine,” says Waters. “But bustards have to be bill-fed.” After a period of quarantine in a special enclosure, they will eventually be released. The enclosure is open-topped to allow them to fly out to colonise surrounding fields. The immigrants have been taught to avoid both man and predators such as foxes using aversion therapy. Volunteers walk through the pen with dogs on leads, and if the birds don't scatter, they bang tin lids or squirt them with water pistols. Adults are, in fact, usually too big to be at risk from foxes. Human egg thieves are a bigger threat, although Waters is not too concerned: “As well as military police, the police, wardens and gamekeepers...there will be a small army of well-wishers and bird-watchers,” he says. “On top of that, half the birds will be radio tagged and all will be fitted with wing tags which can be read from a distance.” For conservationists, the real prize will be the first successful breeding season. Bustards are generally very solitary, only meeting at leks in spring when the males gather to dance competitively, displaying their fluffy wing and tail feathers to the females. After a brief copulation, the two parents stalk different paths with the female laying her two or three eggs in an arable field. When these hatch, she marches her clutch to rough pasture where she feeds them on insects, small rodents and vegetation. The chicks grow very quickly but the males suffer high mortality. “On the other hand,” says Waters, “they are long-lived if they survive and far fewer males than females are needed for breeding.” But Waters concedes he doesn’t know when to expect the new wave of British bustards: “Females can breed in their first year, while males don’t normally succeed until they are four or five,” he says. This is because they are usually out-danced by older males. “Our birds will have no competition so they could start much earlier. If they do, it won’t be before time.” Quick guide