Friday 7 December 2012

What’s That You See, Skip?

It’s a nightly ritual. With just a hint of mystery. I walk the dog before feeding her and putting her to bed. We never go far. It’s out the front door – as often as not with the outside lights off – and across the driveway to the fence.

[a pademelon: hunched and wary]
A tangled vine, some sort of Kennedia, has colonised the fence, screening us from the vacant lot next door. As the dog finds a spot to urinate, I peer over the fence into the dark. I often make out shapes moving in the grass: the small furtive bundle of a bandicoot; the hunched suggestion of a pademelon, and just occasionally the bolder upright alertness of a Bennetts wallaby.

[a Bennetts wallaby]  

Our dog is nearly deaf, so she may not hear them even when they thump the ground in warning. She’s also half blind. But she knows they’re there, straining at the leash, keen to take her knowledge further. In the darkness I too lack visual accuity. I know only by hint, and by long practice, that the dark shape sitting alert is a pademelon not a bush. Some nights I say a soft hello, wondering what it can see or sense of me. I’m sure its vision is far better than mine. But, I wonder, how much better? And what does it actually see?

Zoology has been slow to answer these sorts of question. The strangeness of our marsupials – to European minds at least –  inclined scientists to consider them primitive at best; an evolutionary backwater at worst. When it came to understanding marsupial eye sight, our primate bias literally coloured our thinking. The long-held view was that few mammals – and then only primates – could see in colour. The rest, including marsupials, saw in black and white.

But some clever research at the University of Western Australia has found that marsupials do see in colour, and probably in more colours than we do. The human retina, the light-sensing part of the eye, has two types of cells called rods and cones. Rods help with vision in low light, while cones help with colour vision and detail. The retinas of most other mammals don’t have cone cells, so those mammals don’t see in colour. After the WA research, we now know that marsupials, like primates, have both rods and cones. In fact they have extra sensitivity in their cones, allowing some of them to see in the ultraviolet light range. In addition their vision span is around 300 degrees, in comparison to the human span of around 180 degrees.

[wallaby footprints]  
I guess I should have known about these special marsupial powers through watching episodes of “Skippy the Bush Kangaroo” on TV in the 1960s and ‘70s. In that bush melodrama, Skippy always seemed to come to the rescue of the humans by warning of danger ... (“What’s that Skip? The bank robbers are hiding in the bush!?”) ... or by untying the rope-bound humans (who knew kangaroos had prehensile paws?) ... and even by jumping on deadly snakes so the ranger and his son could escape.

Perhaps science has at last caught up, and can now explain why “Skip” was always a step ahead of the bad guys. She could see so much better than the humans, thanks to her wider vision and ability to see further along the spectrum.

["I'm watching you." A well-dressed pademelon.]  

Next time I’m weeing Noo late at night, I’ll have a new respect for “Skip” and her friends. As they peer back at me through the gloaming, I’ll be aware that they’re seeing a lot more than I’d previously guessed. I might even have to dress a little better, making sure I’m colour coordinated. It doesn’t do to upset the neighbours.

No comments: