Animal World Records
A few weeks ago, in one of our British Wildlife of the Week articles, we looked at the goldcrest and the firecrest – the two smallest birds in Britain and Europe. But although they are undoubtedly miniature marvels in their own right, they’re not the smallest birds in the whole world. That title goes to the bee hummingbird.
At around 5 cm long, with a mass usually no greater than 2 grams (that’s less than the weight of a 5p coin), the bee hummingbird makes goldcrests look like giants. This truly diminutive bird is, as its name suggests, scarcely bigger than some of the world’s largest bee species, and it’s positively dwarfed by several tropical butterflies that share its Cuban forest home.
The smaller the bird, the smaller its wings – so the faster they have to beat to produce lift. All hummingbirds flap their wings so fast that they are a blur, and the resulting humming noise gives this group of birds its name. The bee hummingbird must beat its wings around 80 times every second just to stay aloft, and this number can increase to an astonishing 200 times a second during the male’s courtship display. However, there is a limit to the speed at which electrical signals can pass down a nerve in order to trigger a muscle. The bee hummingbird’s wingbeat is thought to be on, or very close to, the edge of that limit. The reason there are no smaller birds than the bee hummingbird is because one probably cannot exist .
Small size in warm-blooded animals is usually associated with a furious pace of life – and hummingbirds are no exception. These bejewelled little birds are truly hyperactive; they have the most energy-expensive lifestyles of any bird on the planet and seem to do everything at breakneck speed. To fuel their tiny bodies, the fires of metabolism burn fiercely, and their internal organs work just as fast as their furiously-beating wings. The heart of a bee hummingbird – which, incidentally, is said to be the largest, relative to body size, of any warm-blooded animal – can beat at over 1,200 times a minute when flying. Meanwhile, it has a breathing rate of around 250 breaths per minute at rest, and an even greater one when it is active, in order to feed oxygen to enormous wing muscles that comprise almost a third of its weight.
This miniature bird sustains itself primarily with sugar-rich nectar, occasionally supplementing its diet with small, soft-bodied insects and spiders. Its digestive system can process food at a startling rate. In just a single day, a bee hummingbird can visit 1,500 different flowers and drink one-and-a-half times its own body weight in nectar. If a human attempted to drink so much liquid in a single day, they would be dead long before they could accomplish it. But fortunately, hummingbirds have very heavy-duty kidneys to cope with all the nectar passing through them. They are, in fact, one of the few birds that can manage a water surplus by excreting (extremely diluted) liquid urine. If nectar is plentiful, a hummingbird’s daily urine output may exceed 80% of its body weight.
Hummingbirds are fascinating animals, and one of my very favourite group of birds. Their beautiful, iridescent plumage makes them look like tiny flying jewels. Even some of the names we have given them reflect this – just take the fiery topaz, for example, or the amethyst-throated sun angel, or the green-breasted mountaingem. They just sound exciting, colourful and exotic, as I’m sure you’ll agree. Certainly, one article alone cannot do this remarkable family justice – and for that reason, we’ll be looking at hummingbirds in more detail in a future post.
 It should be noted that there are, of course, many insects smaller than the bee hummingbird that can fly by beating their wings – but insects fly in a different way to birds. Their wings are fixed to their exoskeleton, which they can vibrate using simple muscular contractions. To put it another way, think about how one sharp tap can make a tuning fork vibrate. Insects, therefore, have no need to send separate electrical impulses to initiative every single wingbeat. This allows some midges to beat their minuscule wings an almost inconceivable 1,000 times a second!