All that glitters

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