View From The Shed by Shaun Finnie - UP ABOVE THE STREETS AND HOUSES

UP ABOVE THE STREETS AND HOUSES

Anyone above a certain age (like me) will no doubt be singing along to the title of this week's blog. It's the next line that is the main thrust of this piece - “Rainbow flying high”. If this means nothing to you then you should ask someone from an older generation. Find me at RSPB Old Moor's Welcome Shed and I might even sing it to you. Maybe. It's the theme tune to an old children's TV show.

The point that I'm eventually getting to is that there really is a rainbow flying high above us every day, in the colours of the birds that take to the air. It's a laboured theme I know, but stick with me; it will get interesting later. I'm going to get scientific here for a bit too. If it's too much, just skip this one and we'll see you next week. Conversely, if I simplify something too much, please forgive me. I sometimes have to dumb things down so that I can understand it. So here goes, it's Volunteer Shaun's Easy-Peasy Guide to Bird Colouration!

Birds' feathers come in almost every conceivable colour – we'll get to that 'almost' later – and for a variety of reasons. Many use their colouring for camouflage. Think of the many Little Brown Jobs that annoy us birders by looking pretty much the same as each other while they flit from one piece of cover to the next. Even if you've seen which bush they've flown into it's often impossible to see them within it. That's excellent camouflage in action.

Other birds use their more gaudy plumage to attract a mate or to show their strength to others of the same gender. It's usually the males (but not in every case) who dress up in their finery come breeding season. “Look at me! I'm available and I'm the best there is.” A Mandarin Duck is a great example of this. He's just a jumble of bright colours, simply to look as impressive as he can, and doesn't he make a marvellous job of it?

The most common paint jobs that we see in our native woodland birds are browns, greys and blacks. This is caused by the melanin produced naturally in the birds' body. Other colours ranging through yellow, orange and red can be produced in a healthy bird from carotenoids that it receives through its food, perhaps from plant-eating insects.

Of course I'm working on the assumption here (and it's not an unreasonable one) that you're seeing these colours through human eyes. But the truth is that birds see in a different spectrum to us and their feathers are designed for their eyes only. For example, to us humans all adult Blue Tits look pretty much the same. When viewed through an ultraviolet lens however, the blue crown of the males shows up much brighter than that of their female counterparts. As the Blue Tit (like most birds) can see ultraviolet colours very well, they can tell the difference between sexes at a glance. Beauty, in this case, is very much in the eye of the beholder.

But not all feather colouration is as it seems. Take a deep breath because this is where it gets difficult. I hope you paid attention in physics class, because that's where we're going. Remember I said that “birds' feathers come in almost every conceivable colour”? Well that 'almost' colour is blue. Prepare to have your mind blown... There is no bird in the world that has blue pigment in its feathers. Take a moment for that to sink in. Kingfishers. Peacocks. Jays. Those little Blue Tits with the ultraviolet bits. Even the famous Bluebird that has never been known to fly over the White Cliffs of Dover. None of them are actually blue. Every one of them has brown or grey feathers that, through a combination of optical illusion and the restrictions of our own eyes, appear blue to us. Read that again. Kingfisher and Peacock feathers aren't blue, they're brown.

This is due to something called Structural Colouration, where the microscopic shape of the feather (usually caused by air bubbles) influences the way that the light waves bounce off it. Light rays of the other colours of the spectrum are absorbed by the basic brown feather but these bubbles are just precisely the right miniscule size to reflect only the light rays travelling at the wavelength that we interpret as blue. Crazy but true.

It's not only seemingly blue birds that get their colouring this way. Just about every green bird that we see in Britain is actually yellow. I know, it's difficult to get your head around isn't it? As we all know, blue plus yellow equals green, so a bird that may appear green does the 'air bubbles in its feathers to appear blue' trick described above. It then overlays the feather with a tiny layer of yellow pigment and, voila! Instant ability to go invisible in a tree. Apart from the fact that it's not instant (having taken tens of thousands of years of natural selection to get to this point) and not actually invisible. You know what I mean though. You gotta love the way that evolution works.

If you want reds though then the bird's natural amino acids come into play. They create porphyrins which are used to produce vivid red, pink and fluorescent coloured feathers. It can be a bright world if you're a bird. It's such a shame that we humans can't produce the same pigmentations on demand. The world's tattooists would become redundant overnight.

So there you have it. This week's blog has been a difficult but hopefully interesting lesson. If you've made it this far, congratulations! Come back next time when, I promise, normal levels of silliness will be resumed. In the meantime, here's what's been seen at Old Moor this week, both the bright and the dull – but all are beautiful.