The world is full of the most diverse and amazing creatures, leading strange and marvellous lives. Here are three, of many, species that perfectly illustrate why nature inspires us with wonder time and time again.
Melodious warbling and angry chattering are not the only audible ways birds have of communicating their mood and intentions. The male broad-winged hummingbird, for instance, is one of several birds, including many other hummingbird species, which makes use of specially adapted wing feathers to create sound.
The shrill noise of the broad-winged, which was studied in the mountains of Colorado, USA, comes from the tips of two feathers on each wing – the ninth and tenth primaries. These two feathers are slightly narrower and more tapered at the ends than the others and, when the bird flies rapidly, wind rushes through the gap between those tapered ends and produces a high pitched buzzing whistle.
These ‘wing whistles’ seem to be employed in protecting a mating and feeding territory from other males, not only their own species of hummingbird but also other species passing through on migration.
To a tiny bird, these aggressive sounds must be alarming, as they’re loud enough for the human ear to detect 100m away. So a territorial male charging at a rival must be akin to being seen off by a warrior in full battle cry.
The crested pigeon in Australia, by contrast, uses its wing whistles to warn its flock of danger. Because a startled bird takes off faster and at a steeper angle than usual, a narrowed outer feather on the wing gives off a shriller sound than is normally heard when the pigeon makes a more leisurely departure.
Yet another use for feather noise is employed by the club-winged manakin in the cloud forests of the Andes in South America. It vibrates its wings at such a speed that it produces a sound rather like a note on a violin which resonates at 1500 hertz – 1,500 cycles per second. One club-shaped feather vibrates against a neighbouring ridged feather rather in the way that a cricket vibrates its wings to issue sound. This soulful note echoes around the forest as the bird searches hopefully for an answering female.
Winning by a neck
The long necks of giraffes have fascinated scientists for hundreds of years and studies have solved how these ruminants cope with what could be considered a huge inconvenience. The cervical vertebrae of the neck only number seven, the same as any other mammal. But they measure up to 25cm (10in) each and to make this great length as flexible as possible they connect with ball and socket joints, rather like our hips and shoulders, to give much better overall movement.
The vocal chords of a giraffe are at the head end, and therefore air from the lungs has to be pushed a long way to pass over them. For this reason giraffes tend not to vocalise too often but use their heads to mime communication, turning their heads suddenly and staring at what might be a threat, for instance. They breathe much more slowly than other species and their trachea is narrower. This minimises the amount of ‘dead air’ in their breathing tube, which would require a lot of puff to move it up the neck.
To keep their brains supplied with oxygen their large heart generates twice the blood pressure of other similar sized animals. Their neck is equipped with a pressure regulation system that stops excess blood from flowing into their heads when they lower them to eat or drink. High blood pressure would ordinarily cause leakage from the capillaries in their lower extremities, but their very tight, thick leg skin prevents this and keeps the circulation going.
So that’s how giraffes cope with their unique anatomy, but to date there is no definitive answer as to why they evolved that way. There are two traditional speculations. The first is that drought conditions millions of years ago forced the adaptation so that they could browse the topmost branches of trees and give themselves more foraging options. Doubters point out that that’s why they developed long legs and 46cm (18in) tongues, so the neck elongation wasn’t strictly necessary. And, say the sceptics, why did no other animal of their type react to tough conditions by stretching upwards?
The second reason is that male giraffes spar with rivals using their long, necks to swing their bony horns, the ossicones, into the opposition’s body. So sexual selection favoured the males with the strongest, whippiest necks. The nay-sayers observe that a female giraffe’s neck grows just as vigorously throughout her life and, in fact, takes on mass faster than a male’s.
A combination of these two theories could be the answer – that the feeding environment for the giraffe’s shorter-necked ancestor changed between 14 and 12 million years ago, forcing them to increase their foraging options. The males’ increased neck length was then exploited to gain an advantage over other males, giving natural selection further rationale to continue the change.
Itty bitty Brookesia
One of the world’s smallest reptiles is Brookesia micra, a tiny leaf chameleon that lives exclusively on the little island of Nosy Hara, off Madagascar. The adult grows to just 30mm (just over 1in) including the tail, and a juvenile is so small it can stand on the head of a match. They wander through the leaf litter during the day and at night climb trees to sleep at the lofty heights of 10cm (around 4in).
Their diminutive size may have come about because of insular dwarfism, a condition where mammals that became isolated in confined circumstances, such as on an islet like Nosy Hara, decrease in size over several generations to cope with limited habitat and feeding opportunities.