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Native Californian, biologist, wildlife conservation consultant, retired Smithsonian scientist, father of two daughters, grandfather of 4 small primates. INTJ. Believes nature is infinitely more interesting than shopping malls. Born 100 years too late.

Sunday, February 11, 2007

Woodrat tricks codger (continued)

Wood rat couldn’t cut the mustard when it came to climbing down a vertical quarter-inch cord. But could he walk across the same cord if it were horizontal? I pulled a quarter-inch cord taut like a tight rope, and repaired the vertical cord that he had almost chewed through. The next morning the vertical cord was dangling and the bait cup was gone. The pictures tell the rest of the story.

He had fed intermittently for a half hour, and cut the bait free in less than a half minute. I revised my thinking. Making the first cut beneath the food wasn’t so dumb after all. If he cut the rope above the bait it could drop into a thicket below, and that would mean a lot more work. Better to cut it free and haul it home in one set of actions.

There was no sign of the cap that held the peanut butter. He must have cached it in his nest for bedtime snacking. I repaired the set up, and the next night was a repeat performance.

Now that wood rat was a habitual visitor, I expected he would go to any length to reach the reward. So I replaced the 1/4" cord with a 1/8th" nylon cord. I figured a really good climber would hang-crawl along the string to reach the feeding station.

Wood rat would have no part of it. On the next two nights he visited the access route as many as 8 times a night, but would stop where the 1/4" line was knotted to the 1/8" line. There he would look longingly in the direction of the bait. It seemed that wood rat wouldn't walk the line if it was less than a quarter-inch thick.

So far, so good. But now I wondered . . . was wood rat capable of "chimney stemming", — that’s what rock climbers do when they brace themselves and "inchworm" between two parallel walls. I wired a 26" length of 2" PVC pipe, the chimney, between an overhead branch and the platform. The only way he could reach peanut-butter-land, I thought, was to go down the tube. I set one camera trap to monitor the tube entrance, and another to monitor the bait station below.

He visited the bait station for two nights, and I assumed that he was chimney stemming.

But a little knowledge can be dangerous. The picture of the hind-foot hooked over the twig showed that he can't rotate his ankles and cling like a squirrel. Therefore, I thought he was testing it in this picture. He couldn't possibly go down the outside of the tube head-first. He had to be going down inside the tube.

A simple test could prove it. I stuffed an old sock--yes it was clean--into the entrance of the tube, predicting that he would either pull it out and proceed down the tube as usual, or have to forego dining at the bait station.

When I looked at the pictures the next morning, I realized the rodent had tricked me.

He didn't remove the sock, but there he was on the platform eating the peanut butter. Damn! My design was flawed. I had allowed him two options--go up the post or come down the tube. Not good experimental design. My early assumption that he couldn't climb the 3/4" aluminum post had been wrong. Now I was wondering if he ever came down the tube at all--inside or outside.

So I removed the tube to see if he could climb the post.

Surprise! The next morning's pictures showed the rat on the platform.

He could have gotten there only by jumping, levitating, or shimmying up the post. There were no climbing action shots, but there was this picture of him on the verge of descending with a mouthful of peanut butter. I had the feeling I was finally getting closer to the truth.

If you think you can bear any more of this, stay tuned for the final episode.

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