Eye in the Sky
Charlie Portlock gives us the facts on why ultraviolet light matters to we hunters
Do you know a superhuman? If you’ve ever met somebody who’s had radical eye surgery then it’s possible that you do. Recent medical developments have meant that patients with serious cataracts or eye cancer can have their corneas (the lens in the eye) replaced with artificial ones. With around 3% of people this can lead to an ability to see colours in the ultraviolet spectrum, a frequency of light normally undetectable to humans, but integral to the lives of bees, raptors and yes, pigeons.
Humans can see some of the ultraviolet spectrum (UV) under a black light bulb – the kind you’ve probably seen in clubs or light shows, that shows up dust and the white of your clothing. However, we don’t see the full colour spectrum of ultraviolet, only the white and shadows. There’s actually another dimension of visual perception beyond our own. Try to imagine that our world is not actually the colourful place that we think it is; compared to pigeons and raptors, what we see is the monochrome of an old western on an analogue TV, rather than the full-colour, highdefinition image of the modern digital display. Compared to pigeons, we’re almost colourblind.
Humans have three kinds of optical cone cells in their eyes (red, green and blue) and we can see around 7 million colours. Pigeons are tetrachromats and have four of these cone cells – one of them being sensitive to
UV – as well as a kind of coloured oil in each that humans lack. This set-up enables them to see colours in much higher definition, along with the entire UV spectrum of light. There’s literally another world, another frontier of colour, that’s invisible to us.
Pigeons also have almost twice our ability to detect and process movement. They are tasty birds, so they need to be able to avoid aerial predators like peregrine falcons – the fastest bird on earth – as well as correctly plot their landing within dense foliage whilst flying at high speeds. If you’ve ever ridden a bicycle on an aggressive downhill, you’ll know how fast 25mph can seem when you’re in a small vehicle. If a relatively small pigeon experienced velocity in the same way that we do, it wouldn’t be able to process visual information at the necessary speed to ensure a safe landing.
At 60 cycles per second we cannot detect a flashing light like a strobe or a projector, seeing it as a continuous beam. This compares to 90-110 cycles per second for pigeons who would see a modern digital film as a series of slides. With this kind of acuity we can expect pigeons to be about twice as sensitive to movement as we are. They, like many birds, may also experience the world in a kind of slow motion, unless in flight, in which case things would probably appear ‘normal’. If you’d evolved to be in your element on the wing at 70mph, then feeding on the ground or roosting would seem rather sedate by comparison, making any untoward movement from approaching predators – including airgunners – that much more obvious.
Many birds have feathers that use ‘structural’ colours – the ones we can see easily – for display purposes, but since the 1980s researchers have been aware that the feathers of many birds reflect UV light, often making their plumage appear completely different and significantly more complex to other birds. To begin to appreciate patterns of avian plumage, scientists use a spectrophotometer which approximates how birds might see. They’ve have made some interesting discoveries; for example, the humble blue tit is difficult to sex with the human eye, but the birds themselves have no trouble because the crown of the male specifically reflects UV light. This kind of new knowledge has many implications for those studying bird behaviour, including hunters.
WHITER THAN WHITE?
Optical brighteners are used in all commercial detergents, and some soaps and shampoos, and are used to create the dazzling white effects that we’re so used to seeing on adverts. Vanderberg Air Force base in the US instructs their men not to use laundry with optical brighteners because it makes them more visible at night under artificial light, as well as through infrared optics. It’s standard practice in the US Forces to avoid detergents containing these ingredients for reasons of safety against snipers, but you probably don’t want to wash your hunting clothes with this stuff – best stick to water and elbow grease.
There’s another factor. Many modern clothing dyes reflect UV light, so your photo-print digital camo might not be as efficient in disguising your presence as you think. If you’re wondering if your clothing is as stealthy as advertised, then you can test it by buying a small black light and taking a good look in the dark. If your clothing shines, then you can be sure that a pigeon, or any other day-flying bird, will be able to see it, too. Sports wash or technical detergents along with UV ‘ killing’ sprays can counteract this effect, but these solutions are hardly ideal.
Clothing manufacturers might not like this information, but for pigeon shooters lurking in shadow or using artificial hides, the role of UV in concealment should not be underestimated. I’m not suggesting that we’ll always stand out like a beacon when wearing these fabrics, but in certain lighting conditions, when using certain equipment, we might be significantly more obvious than we realise. In short, if we’re shooting pigeons or any other bird species, then perhaps we should be camouflaging in the fourth dimension.
If you’ve ever wondered why that buzzard sits idly in his tree, it’s worth remembering that animal urine and faeces are also reflective to UV and that birds of prey can actually plot the territorial markings of small mammals, like voles, and follow them right back to their nests as if on a runway. Raptors can see both the distant and the zoomed image simultaneously, and if they already know where to look from the urine trail, it’s just a question of waiting for their prey to turn up. Nice!
Unlike raptors who have the binocular sight typical of predators, pigeons have largely monocular vision. Each eye sees to the side of the body in a wide arc and these arcs of sight are like two semi-circles that hardly cross. As you’re reading this page, the image is duplicated in both eyes. Not so for pigeons; they have relativity poor depth perception for which they compensate by bobbing up and down when moving because this helps them to orientate with their surroundings.
Berries, nuts, grains and seeds also reflect light in the UV spectrum, unlike most green leaves, which makes them easer for pigeons to spot.
In 2008, the pigeon passed the ‘mirror test’ – being able to recognise its reflection in a mirror; it is one of only six species, and the only non-mammal, that has this ability. A human child is typically around three years old before it has this level of cognitive function.
THE WIDER VIEW
Moving forward, there’s a lot more work to be done around how animals experience the world on both a physical and cognitive level. As hunters, it’s convenient for some of us to underestimate our quarry, to see the creatures we hunt as vermin or ‘ lower animals’. This is surely a mistake left over from some archaic biblical idea that we’ve been put on this earth to lord it over the ‘ lesser beasts’. The truth is that modern scientific research is showing us just how much the animal and plant worlds have to teach us, and there’s a lot to learn. When we start to investigate the physiology and behaviour of even a common creature like the woodpigeon, it’s surprising what incredible things it has to teach us.
An ability to step out of our own sensory world and into that of our quarry enables us to become better hunters, but even more importantly, it’s a reminder, that we’re not the most highly evolved creatures on the planet. All animals are perfectly adapted to live successfully within their respective habitats – apart from humans, it seems – and through a better understanding of these adaptations we are able not only to put more food on the table, but also to approach the natural world with a little more humility. We’re not better, we’re just different. Best of luck in the field, Charlie.
Beards don’t reflect UV, thank goodness
We all know not to wear white, but does our camo glow to pigeons?
Is this what a pigeon sees?
This is what camo looks like to our eyes
“Unlike raptors who have the binocular sight typical of predators, pigeons have largely monocular vision”
I was lucky with these two
The USAF says some detergents can negate camouflage