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Thursday, 3 May 2012

More about animal tracks

This follows on from The mysterious cloven-hoofed animals of Australia.

These two photos are old slides (notice the lens cap, used as a scale!).

The shots show late afternoon tracks on a beach.

No matter what sort of animal you are after, tracks in sand are seen best when the sun is low in the sky. That means winter is better than summer, but early morning and late afternoon are much better, because the high and low parts are contrasted better. (This also applies if you are looking for Aboriginal rock engravings, or when you are looking at the impressions on a sheet of paper, left by somebody writing on the sheet above.)

If you live near sand dunes (or can get to some), you will have no shortage of animal tracks to study, but the problem is that most of the time, you won't know what made the tracks.

The best way to collect tracks in your backyard is to leave out either food or water in the middle of a patch of smooth, dry sand. To keep it dry, you may like to rig a temporary awning of "poly tarp" or something similar, or use a tray that you can take inside when it rains. Then you just need to observe carefully. Once again, you won't know what made the tracks, though I will come back to that later.

An easy way to get tracks that you can identify is to use captured animals—you can always let them go later.  You will need either some flat, dry, clean sand, or a large tin lid, candle, pliers, large spider (orb-weaver or a huntsman) or a lizard of reasonable length (say >10 cm long) or a large beetle.  In what follows, I will just say "spider", but feel free to improvise or change the animal.  Basically, I am suggesting that you try this old method as a starting-point, and see if you can adapt it.

In either case, you will need two pieces of wood about 30 cm long.  You will probably need a jar with a lid and some cardboard or a brush to catch your test animal. You will definitely need a large water container like a baby bath and some bricks or wood blocks. Most experiments like this work best when the apparatus is set up in a large dish like a baby's plastic bath with some water in the bottom. Set everything up on wood blocks or bricks, and use the water as a sort of moat to keep the spider from escaping.

Spiders are most easily caught in the evening, after they have made their webs. Take the jar and use a camel hair brush to urge the spider to move in the right direction then catch it as it drops off the web.

I don't recommend getting snake tracks using any
other method than the one I used here, where I
took my shot after the snake was well and truly
Light a candle and use the pliers to hold the tin lid over the flame, moving it around until the whole of the surface of the lid is black. Watch out that you don't get burned!

Once the lid has cooled, you can let your spider walk across it between the two pieces of wood, to collect spider tracks. You will get a neater result if the wood pieces rest on something else, like two matches, and don't touch the tin lid. You could also use an old light-coloured dinner plate instead of a tin lid.

For comparison, try the same large spider on smooth dry sand. Does it leave a track?

Note: the lid/plate method works well with beetles, centipedes and lizards. Catch a flat spider, the sort which lives under the bark of gum trees, and compare its tracks with those of an orb weaver. After you have collected a variety of spider tracks, see whether you can learn to identify a species by the track it makes. (I tried this and I couldn't!)

Next time, I'll say a bit about tracks in mud.

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