The Nature of the Beast (according to Susan McCarthy)

Like furry spoons

There were two northern treeshrews in a glass-fronted cage in the National Museum in Washington, DC. The female scampered along a tangle of branches, up, down, over, under, back, up, over, down, over, down, etc.

I was busy myself, leaning on a wall and sneering at the sign. It identified the treeshrews and gave the remarkable fact that their milk is 25% fat, whereas human milk is only 4% fat – but it didn't say why. It said nothing of the amazing “absentee maternal system” (see 4/23/08 post). Since the babies only get one fast shot of milk every other day, there has to be enough fat in it to last them. Why didn't the sign mention that?

The slightly larger male treeshrew suddenly ran to the female. She waited as he sniffed urgently under her tail, and braced herself in place as he initiated a quick, vigorous sex act. Then she raced off to do some more scampering. The male scampered more slowly to another branch, sat, and looked around.

People passed by, glanced at the two treeshrews in the cage, said “rats” or “squirrels” and passed on. Occasionally someone read the sign and said “northern treeshrews.”

The male treeshrew focused on the female, scampered to her, sniffed, and initiated another speedy mating. As soon as it was over, the female dashed away again. The male would go sit on a branch until he once again found the female irresistible. In ten minutes, they mated eight times. One passing family glanced at the treeshrews, noticed the activity, and observed with interest until, apparently, it suddenly seemed to the mother that this might be unsuitable for her son (a kid of  8 or 9). “Rafael!* Come!” she said sharply, pushing the stroller to the next cage. (*I have changed this kid's name to protect the family and out of sheer mockery.)

Another woman with a stroller came by. She spotted the scandal, and sang fondly to her child, “Babies! There's gonna be babies! Baby chipmunks!”

Finally, the male treeshrew climbed to a high branch and lay down along it in a pose of utter exhaustion. The female, still energetic, did some scampering, glanced at the male, and hurtled up to the branch where he lay. She nestled up behind, put her front paws around him, and lay there holding him. There the two remained, quite still.

If you walked by and saw them then, it would have been a dull sight.

Photo: Guérin Nicolas

The Dangerous Lives of Treeshrews

I was reading Tupai: A Field Study of Bornean Treeshrews by Louise H. Emmons because that is the kind of thing I like, and learned about the absentee maternal system found in some treeshrew species.

First I should say that treeshrews are the same as tree shrews, and the closing up of the word is probably meant to indicate that they don't really live in trees and they're not really shrews. This is a case of TC, Taxonomic Correctness, like the argument that you should call a starfish a sea star because it's not really a fish. Oh please. But a big issue about treeshrews is whether they're descended from very primitive primates and so are our distant cousins, or whether the connection goes further back so that the primates and the treeshrews are both descended from the clade Euarchonta, making them even more distant cousins. I have no opinion on this.

In the absentee maternal system the mother treeshrew builds two nests (yeah, in trees). They are far apart. She puts her babies in one and she sleeps in the other one when she's not racing around snuffling through the leaf litter and catching bugs. Every other day she secretly visits the babies, taking a different route each time, and nurses them. When she's not there the babies lie still and don't make a sound. If an intrepid wildlife biologist like Louise H. Emmons takes a baby out of the nest, it lies silently in her hand with its eyes closed.

One day when they are old enough the mother treeshrew drops by as usual, but instead of just nursing them she takes them out and shows them Borneo. Here's a bug, here's a little trail, here's what you do when you hear a scary noise -- there's another bug! Let me see you grab it! She brings them with her on her rounds and protects them while they learn the business of treeshrewing.

According to a report from the wild, the babies were "shaky" the first time they came out of the nest hole.

The reason treeshrews do this has to be that it makes it much less likely that predators will find the nest and eat the babies by observing the mother. (That's the sort of creepy trick that jays and crows do, for example.) And obviously it's very convenient for the mother treeshrew. Which makes me lean toward the idea that treeshrews aren't primates – what baby primate holds that still for that long?

Like other wildlife biologists who write books for general audiences, Louise H. Emmons tries to find a balance between the stuff working scientists mostly do, and the stuff that people are actually interested in hearing about. Most of the work of wildlife biology doesn't involve playing peekaboo with baby gorillas, swimming with whale sharks, or filming hippo hijinks. It involves data sets. Perhaps Emmons leans too far in the direction of hard science, because her best story was walled up alive in an appendix. (I read appendices so you don't have to. Or at least I skim them.)

In Appendix 1, Emmons explains why a trapping data set is incomplete.

 

In the January trapping period, a group of elephants went through the study area, systematically destroying man-made objects (rain gauges, signs, trail markers, etc.). They stomped on seven baited traps but interestingly did not step on one that contained a treeshrew, while flattening the two on each side (trapping in January was curtailed, and this month is excluded from most data).

 

The elephants spared the tiny prisoner! Of course I think they did it because they felt compassion for the treeshrew, but I realize that there is also a compelling quality to  the explanation that they did it because they didn't want to get their feet sticky.