Rodentia

This is a story about squirrels and chipmunks. When you’re dealing with rodents, there is always the possibility of things going awry. Part of the work here involves modifying habitat so that it is more suitable for plants and animals that are losing ground in the competition for habitat, or succumbing to encroachment from aggressive invasive species. You might think that squirrels are not endangered since they are so common in urban areas, but it turns out that our own Western gray squirrel, (as opposed to the non-native, ubiquitous and annoying Eastern gray of the city) are listed as a sensitive species in Oregon, and threatened (one step before endangered) in Washington State.

The handsome Western grays – silver-grays in the local parlance – are larger than Eastern grey and fox squirrels and have white hairs that give their fur a silvery appearance and sport very big bushy tails. Western gray squirrels are denizens of oak woodlands, and of course since this habitat is much reduced, their numbers are falling. Eastern grey squirrels out-compete them in the same habitat, and they have also been over-hunted as a game species.

Our squirrel habitat project was especially fun, because as Dean (our contact at the conservation district) was learning new things, he passed them on to me. Dean had already scoped out a new section along the savanna and woodland for native squirrel habitat. The first step was to identify the species that were present, if any, using a hair trap (see below).

The trap is a tube baited with acorns or hazelnuts and some of that heavy double-stick picture hanging tape. When the squirrels go in the tube, the tape grabs a few hairs off their back. If you happen to have access to a squirrel expert, (as Dean did) she can tell you if it is a native or a non native squirrel by looking at the hairs microscopically. Our squirrel hairs were from a native. The forensics were a success.

Dean with his hair trap

Squirrel hair trap in place with goodies

Got the hairs!

Now that the squirrels were confirmed, habitat work began. This consisted of getting rid of firs and thinning out some oaks to allow the remaining trees room to bush out and form a continuous canopy. This makes it easy for squirrels to jump from tree to tree. Larger trees offer better nest sites too, because they have larger branches and may have holes the squirrels can use for nests. Gray squirrels also use the edge of the forest near the open savanna, and I’ve seen them near the house in the firs as well, so they seem pretty opportunistic.

The Doug firs and some crowded oaks were killed by girdling – chopping through the outer living layer all the way around the tree to cut off the flow of fluids. The land was too steep for good machinery access, and this method was less expensive, quicker, and had the advantage of creating some standing dead wood for future habitat for woodpeckers, owls and other critters.

As fungi soften up the wood in a dead tree by digesting the carbon, many organisms will move in. Beetles and other insects can be in living or dead wood; woodpeckers come looking for insects to eat and make holes which can offer nesting cavities for squirrels and owls and other birds. A dead tree on the ground or standing will end up have more biological action going on than it did when it was alive.

Cavities in living or dead trees are part of a diverse structure in either oak or fir woods and are normally present in older stands, but not usually tree farms. Processes that create structure for habitat naturally (broken branches, fungus, insects) will produce a “messier” look, which is normal. In the absence of a lightning strike or whole tree death, mechanically limbing and topping will create an artificial snag.

Girdling a tree makes it eventually fall over, breaking at the bottom where the cuts were made. Not so safe if you’re walking around, plus it doesn’t last as long as one that is top-killed. Topped trees tend to “melt” according to the cutter who made our snags. Altogether a longer-lasting and safer option. Since topping is a fairly expensive operation, we chose just three of the largest firs for this treatment. Some limbs are left on to prolong the life of what tree is left after the gory operation:

Tree before topping begins

Most of limbing complete. Climber checking the wind before the final cut on tree #1

Tree climber cutting the top off the third tree

The topping was pretty dramatic. It is exciting to see a fast tree climber work on these snags. See it in action:

 

Here is the view a few months later. It looks devastated, but the oaks will fill in over time and there will be lots of value in even the smaller dead trees as they decompose and offer perching spots as well as a carbon supply to the decomposition process.

dead trees and a snag a few months after girdling to open up oak stand

Two of the tall snags on right and left background of photo

southern edge of the Land of Moose & Squirrel w/ snag and oaks

 

That’s not the end of the squirrel story though. I often caught site of what looked like a gray squirrel on the ground near some of our outbuildings. It seemed quite at home on the ground. Hmmm … eventually some little squirrels materialized, and our dog seemed very excited to go out to the brush and wood piles in the yard. Could it be that a female decided she preferred the brush piles to the trees? I had never seen any reference to nests anywhere but trees, but we kept seeing these critters on the ground, running towards a hole in the ground or one of the wood piles. After consulting my Living With Wildlife book (chipmunks: small golf-ball sized holes; squirrels: baseball-sized holes), turns out, we have yet another species of native squirrels: the also handsome California ground squirrel aka gray digger. As the habitat opens up with farming and the climate warms, they feel more and more at home here. And they love to dig a big network of tunnels right under buildings if a boulder isn’t handy.

There seems to be a family of two kids and a mom. They forage quite busily every morning on green apples and seeds from various trees in the yard. Ominously, they have now intersected with a bunch of chipmunks tunneling under the house and possibly living in the crawl space.

That’s what happens when you live in the woods – everyone picks their favorite spot, heedless of the wonderful natural habitat that might be just a little less comfy than your human one.

The next strategy was to see if we could get the squirrel and/or chipmunk in a live trap to make sure they were not under the house, then build some barricades. I had originally gotten a chipmunk-sized live trap, but I thought I’d see if the squirrel would fit. Sure enough – the trap was just big enough to accommodate a (smallish) agitated California ground squirrel.

Squirrel and trap next to entrance hole

We covered the trap with a towel and walked her up the hill to the official “habitat” which Tom had christened the Land of Moose and Squirrel. As she burst out of the cage, I remarked that she would probably be waiting for us when we got back to the house. Which, in fact, happened. Turns out, the trees are not where the ground squirrels prefer to be.

Step two of this process, as advised by the trusty “Living With Wildlife” was to dig a trench along the house, line it with hardware cloth, and hope for the best (that last bit is my own).

the strategy – dig an even bigger hole and barricade with wire

This was beginning to feel like an arms race – small hole, large trench, what next? I finished filling in my trench, hoping it would be sufficient to foil the rodent that, after all only has its claws as tools, but they are called gray diggers for a reason. There have been some exploratory holes in the old spot, but so far I’m ahead. The chipmunks are determinedly working on getting back in.

A day or two later, an alarmed-squirrel sound outside inspired me to try to get close enough to take a couple of photos. This was indeed our wonderful Western gray – bigger bushy tail, silvery grey. She was barking at the cat, which probably does not outweigh her, and for once this tree squirrel did not mind me getting within range. Gray squirrels make an interesting chuckling sound. At the same time she was drumming on the tree branch with her claws, sending a complicated message to whatever other creatures could speak squirrel. Perhaps the ground squirrel,which also climbs trees.

So far the troublesome ground squirrels seem to be gaining each year and the gray squirrels are fewer and more shy. It will be interesting to observe them both in the coming seasons.

Western grey squirrel up a tree – where it belongs

Western grey squirrel in scolding mode

 

3 thoughts on “Rodentia

  1. Pingback: Time. Maps. Closeup views | GOPHER VALLEY JOURNAL

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