All that glitters
BBC Wildlife|September 2021
Dazzling in flight and in colour, hummingbirds have long captured our imagination. But these spectacular birds are vulnerable to a changing world.
Jon Dunn
As dawn breaks in a northern wood – one that, at first glance, doesn’t look terribly different to the deciduous woodlands of Britain – a hummingbird is stirring. The spring night here, only a few hundred miles south of the Arctic Circle, has been long and cold. It could have been fatal for a bird that weighs little more than a penny, let alone one with a metabolism as fast and specialised as that of a rufous hummingbird. Hence, he hasn’t just slept; he’s spent the night in a state of torpor.

His heart has slowed from a daytime rate of 1,200 beats per minute to less than 100 beats per minute, which, for a hummingbird, is barely ticking over. His body temperature has dropped too, by some 26°C, to just a few degrees above the chilly ambient air temperature. To put that into perspective, were our body temperature to drop by 2°C, we’d enter a state of hypothermia. To all intents and purposes, this hummingbird is coming out of a state of near hibernation.

Fuel in the tank

Extremes of exertion demand a lot of energy. The recommended daily calorie intake is 2,500 for men and2,000 for women. But if we had the metabolism and energy requirements of a hummingbird, it would increase to approximately 155,000 calories a day. Nectar from flowers is sugar-rich and provides the energy hummingbirds need. They cannot, however, live on sugar alone – they supplement their daily diet with protein in the form of small insects and spiders, which they hunt when not visiting flowers.

Rise and shine

Waking up, for him, involves more than just a stretch and a yawn. He needs to find food, and soon. Hummingbirds’ famous, hovering flight demands about 7 calories per day. It is a high energy requirement for a tiny bird that, for the most part, they satisfy with a diet of nectar. That would be a problem for this rufous hummingbird though, as precious few flowers are blooming so early in the Alaskan spring. He’s migrated here from his wintering grounds in Central America, more than 4,800km to the south, to stake a claim to a territory and await the arrival of potential mates. The northern summer is a short one and he can’t afford to waste time.

In the absence of flowers, he resorts to theft. Sapsuckers are small woodpeckers that drill holes in living trees to create wells in which sugar-rich sap gathers. This is what the sapsuckers feed upon and, when their backs are turned, what the rufous hummingbird pilfers until the days grow longer and warmer, and there are flowering columbines in the woods to provide his own source of sustenance.

Rufous hummingbirds confound what we think we know about their species. For a start, hummingbirds aren’t confined to the American tropics; they can be seen from Alaska in the far north to Tierra del Fuego at the southern tip of South America. In between, in the Neotropics, they occur in great diversity, with hundreds of species known to science and, even now, more being discovered. Some hummingbirds are restricted to tiny, localised ranges and can go overlooked for decades at a time.

They also aren’t as delicate as we might assume for such tiny birds. The largest of all, the giant hummingbird, is hardly a lumbering behemoth (it’s still smaller than a starling), but hummingbirds are tough, feisty creatures. Some migrate hundreds or thousands of kilometres every year in order to breed. Others eke out a living in the paramo, a treeless habitat just below the snowline high in the Andes – Ecuadorian hill star hummingbirds have been seen at a breathtaking 5,000m above sea level. At the other extreme, some species live at sea level in humid mangrove swamps. There’s barely a habitat in the Americas in which at least one species of hummingbird hasn’t found a niche – in arid deserts or dripping cloud forests, on the flanks of volcanoes and in the shadows of glaciers, there will be hummingbirds.

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