Читать книгу Extreme Nature - Mark Carwardine - Страница 24

NAME	broad-tailed hummingbird Selasphorus platycercus
LOCATION	North America
ABILITY	can drink up to five times its body weight in a day

© Mary Plage/Oxford Scientific Films

To say this or any other hummingbird drinks like a fish is to understate how much it drinks. In proportion to its body weight, it drinks a lot more than a fish. (Just to get that cliché straight: freshwater fish don’t drink – they absorb water through their skin. Saltwater fish that drink don’t do so to excess.) In the case of the hummingbird, it’s the fault of the flowers. Hummingbirds have evolved to drink nectar. The flowers they visit have evolved to provide that nectar, and the nectar they provide is typically about 30 per cent sugar and the rest water. To keep their wings going at a rate quicker than the human eye can see – to hover – hummingbirds need a huge amount of sugar, which means that by drinking nectar they take in up to five times their body weight in water every day.

If any other animal, including a human, tried to drink even one times its body weight, it would be dead long before it could do it. So while hummingbirds were evolving beaks to fit into the flowers with their watered-down nectar, they were also having to evolve nature’s heaviest-duty kidneys. Some water just passes through the bird unprocessed, but 80 per cent goes to the kidneys to be expelled as very dilute urine. And why the broad-tailed in particular? It’s simply the most energetic hummingbird, and thus the most supersaturated.