View From The Shed by Shaun Finnie - SENSES WORKING OVERTIME (PART 1)

SENSES WORKING OVERTIME (Part One)

Most humans have five senses. You know them all. Sight, smell, hearing, touch and taste.

Most birds have the same five, and possibly a bit more too but we'll get to that later. But how do their senses compare to ours? While sight is probably our most used sense, which is most important to them? And how important is each sense to each individual species?

Let's look at some birdy examples of the senses in use.

Sight

All birds can see incredibly well, much better than we humans can. For example, not only can they see much further and more clearly than us but every one of them can, to some degree, see into the ultraviolet spectrum range. In effect they can see colours that we can only imagine. You might know that mice have especially leaky bladders. They leave a small trail of urine wherever they go. That might not seem like much of a problem until you learn that their urine glows bright yellow when exposed to UV light, so given that raptors can see in the ultraviolet range it leaves Mr Mouse quite exposed whenever he's been caught short. The hunter can always tell where he's been. And some birds can see to a precision that is, to us, almost unimaginable. For example some raptors can clearly focus upon a small prey animal a mile away. Even someone with as poor sight as me can see where this is going. Evolution hasn't been kind to mice, that's why they breed so freely.

The point of our eye where the cones are at their highest concentration (and therefore the part where the vision is at its most accurate) is called the fovea. Some specialist hunters such as Kingfishers have two or even three distinct fovea, giving them a kind of switchable binocular vision so that they can instantly zoom in more precisely when required. I wish I'd paid more attention during my O level biology lessons so I could understand and explain that a bit better. You'll just have to take my word for it. Kingfishers can see better than me.

Hearing

Your average bird's hearing is also much more sensitive than your average human being's. They can hear much shorter sounds than us and also sounds at a much lower frequency.

For example, we hear a songbird's trill as a rapid fire machine gun burst of notes. Imagine a Skylark, oozing melody as he rises to a mere speck in a clear blue sky. To our ears his song can be so fast that it blurs into a delightful wall of sound, but others of his species will hear each note individually and judge the bird's singing performance accordingly. If an X-Factor singer gets the most votes in the competition they might win a recording contract with Simon Cowell or something similar. The winner of the bird singing contest gets a much greater prize; he gets a mate. Those lady Skylarks are much more picky than an ITV viewer.

A hunting bird's hearing has to be especially good to hear (for example) its victim rustling through the grass. Not only does it have to hear this smallest of sound but it also has to precisely pinpoint the direction that the sound is coming from. That is why an owl's ear holes are offset in their skulls, one slightly higher than the other. This discrepancy means greater accuracy in directional location. Yet again, Mr Mouse's location is discovered. He's not having a good day.

Touch

Obviously birds don't have fingers comparable to our own, so it's not so easy to see how their sense of touch comes into play. They can't grasp, stroke or strike things in the way that we can, but the sense of touch is much more than that. You only have to see how a feeding chicken or duck moves away if another one nudges into it to see that they can feel the contact. That's part of the 'touch' sense. So is judging the amount of pressure required to crack a nut or seed case with their beak. OK, so maybe touch isn't a bird's most used sense but it's certainly there, just possibly not as sensitive or frequently used as a human's.

There are exceptions though. A Nightjar might not be the prettiest of birds but it has a startling set of whiskers around its beak that are mostly missing from other birds you might see in the UK. Think of a cat's whiskers and you're in the right area, just much smaller. They're sensory organs for feeling the flow of air around the bird's face and (particularly) beak. Nobody knows for certain how this is used but scientists are working on it. It's definitely not, as was once believed, for filtering bits of insect into the Nightjar's mouth. That's just a silly idea. Do you need a device around your mouth to help guide the sandwiches in?

Further afield, the New Zealand Kiwi has such a sensitive beak that it can feel around in the soil for insects, earthworms and other tasty delights. It's beak can sense the vibrations of the moving prey creature and feel the contact, knowing when to chow down. Yummy. Slimy and satisfying.

So that's covered sight, hearing and touch, but what about a birds' other senses. Well, it appears that I've run out of room, which means this week's blog is a first. I've never done a two-parter before, but guess what? Come back next week when I'll examine birds' other senses. They might not be what you think.