Zoologger: The heaviest animal in the air

By Michael Marshall Species: Otis tarda Habitat: temperate Asia, and southern and central Europe, though much of its habitat has been lost At first glance it looks like a squashed ostrich, strutting proudly across the Spanish plain with its head held high. Then it takes off. The great bustard is probably the heaviest living animal that can fly. The males normally weigh between 10 and 16 kilograms, but some can reach 21 kg. For comparison, the wandering albatross has a larger wingspan, but only the biggest reach even 16 kg. Female great bustards are much more petite creatures, normally weighing no more than 5 kg. This is the largest size disparity of any bird species, and it can mean only one thing: females prefer chunky males. But the females aren’t just picking the males for their weight. They have an eye for their necks and whiskers too. Great bustards are a lekking species. At the start of the mating season all the males in an area gather at one site, the lek, to compete for females. The females have the chance to check out all the local males, and to choose the best to father their chicks. The males arrive first, in January, and the females turn up in March or April. Before they do, the males compete and may even fight to establish their place in the hierarchy. The stakes are high: come the mating season, less than half the males will even attempt to copulate, and less than 10 per cent will succeed. Among males, only the most dominant pass on their genes. Male peacocks have fantastically coloured tails, but male great bustards make do with white whiskers. Actually thin feathers, they can be 20 centimetres long and have no practical function other than to look good to females. During display sessions, the males lift them to show off their size. During the mating season, males also develop conspicuous plumage on their necks. Instead of the usual plain grey, they acquire a two-tone pattern: white on the throat, chestnut brown towards the base. Their necks also swell up, and two stripes of bare blue skin appear down their length. As if that weren’t enough, the males have bright white tails that they aim towards the sun to attract females from a distance. According to Juan Alonso of the National Museum of Natural History in Madrid, Spain, and colleagues, the whiskers and neck plumage are signals of quality. Males with conspicuous whiskers and necks are effectively saying, both to females and other males, that they are large and old – and thus both a good mating prospect and a bad rival to challenge. Alonso and his team captured and measured 41 males in central Spain and then tracked them over four years using radio tags fitted to the birds’ backs. They found that heavier animals tended to have larger whiskers, and older animals tended to have better developed neck plumage. It seems that the males’ displays are “honest”: that is, males with better display are actually in better condition than those with poor displays. And the elaborate decorations seem to pay off: better-developed males start displaying earlier in the season, get into fewer fights with other males, display for longer each day, and mate more often. All the males’ fripperies become more pronounced with age. That might seem counter-intuitive: why would a male want to advertise his advancing years? But females often prefer older males, because they have demonstrated their ability to survive and thus are likely to have good genes. Journal reference: Ethology, DOI: 10.1111/j.1439-0310.2010.01827.x Read previous Zoologger columns: Ancient air-breathing, triple-jawed fish, Horror fly returns from the dead, Even parasitic worms have a divided society, Shrimp plays chicken with its sex change, Death by world’s longest animal, Live birth, evolving before our eyes, Sympathy for the piranha, The world’s most fecund vertebrate, Whale-eater’s helpful sulphur-powered guests, Horror lizard squirts tears of blood. More on these topics:
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