Birds
Great Bustard
Otis tarda · also called great bustard
The great bustard is a bird that pushes flight to its physical limit: a male can weigh as much as a medium dog and still, given a running start and a headwind, get into the air. On the breeding grounds the same male turns himself into a trembling white ball to win a mate.
Overview
Otis tarda lives on the open plains and steppes of Europe and central Asia, with more than half the world population in Spain. Males average 10 to 16 kg and can reach around 21, rivalling the kori bustard as the heaviest flying bird; females are a third of the size. It is an omnivore, eating greens, seeds, and many insects.
The foam-bath display
At traditional lek grounds, a displaying male inflates a throat pouch, folds his tail forward over his back, twists his wings to show their white undersides, and pulls in his head, becoming a large white pom-pom visible far across the plain. Females choose a mate and then raise the chicks alone.
Toxic self-medication
Males deliberately eat blister beetles, whose poison, cantharidin, kills gut parasites in small doses. Healthier males display better, so the risky diet may both treat the bird and advertise its quality.
Status
Vulnerable and declining as grassland is ploughed and fenced. Hunted to extinction in Britain by 1832 and reintroduced to Salisbury Plain since 2004, where it now breeds again.
Great Bustard: common questions
Is the great bustard the heaviest flying bird?
It is one of the two heaviest, along with the kori bustard of Africa. The largest male great bustards, at around 18 to 21 kilograms, are at or near the upper limit for a bird that can still get off the ground under its own power, and individual records for the two species overlap, so which one is heaviest depends on the individuals being compared. Both are far heavier than familiar large flying birds like swans or eagles. Beyond that weight, flight becomes impossible, which is why the truly giant birds, the ostrich, emu, and the extinct moa and elephant birds, are all flightless.
What is the male great bustard doing when it looks like a white ball?
It is performing its courtship display, sometimes called a foam bath because of the frothy white appearance. The male puffs out an inflatable pouch in the throat and neck, tips his tail up and forward until it lies along his back, twists his wings so the white feathers on their undersides face outward, and pulls his head down out of sight. The overall effect turns a large brown bird into a quivering mound of white plumage that can be seen from a long way off across flat open country, which is the point, since females are watching from a distance and comparing the males at a lek.
Why did the great bustard go extinct in Britain, and how was it brought back?
It was a large, tasty, conspicuous bird of open downland, and by the early nineteenth century a combination of shooting, egg collecting, and the enclosure and cultivation of its grassland habitat had wiped it out, with the last British birds gone around 1832. A reintroduction effort began in 2004, initially bringing in eggs and chicks from Russia and later from Spain, rearing them with care to avoid taming them, and releasing them on the military training land of Salisbury Plain, which offers large undisturbed grassland. Birds have since bred in the wild there, and the project has established a small but growing free-living population.
Do great bustards really self-medicate with poisonous beetles?
The evidence points that way. Blister beetles contain cantharidin, a compound toxic enough to blister skin and harm the kidneys in quantity, and most animals leave them alone. Male great bustards, however, seek them out and eat them, more than females do, and research has found that the cantharidin dose they take in is high enough to kill intestinal worms and other parasites without poisoning the bird. Males in better parasite-free condition can sustain the demanding lek display for longer, so eating the beetles may both improve a male's health and serve as an honest signal of how much toxin he can handle.