Little Earthmover

Little Earthmover

Ever wonder what a mountain beaver does outside of its burrow?

No?

I guess I'm not surprised. 

Well, have a look anyway.

Here's some footage of a mother and her offspring taken during last summer's Camera Trapping Workshop in the northern Sierra Nevada.

There's not much to say.

Mountain beavers are just like big pocket gophers when it comes to moving earth. 

Slinky grim reaper of the underworld

Long-tailed weasel with prey.

There's a good reason weasels are long and skinny.

It's "essential to the profession of a burrow-hunting rodent predator...", wrote weasel expert Carolyn King.

This photo of hunter and quarry was taken in a mountain beaver burrow, and it would seem to prove the point.

But did this long-tailed weasel kill the golden-mantled ground squirrel in the burrow?  Or did it dispatch the rodent above ground and then drag it into the burrow?

Golden-mantled ground squirrels are common in the area, but you find them in dry open coniferous forests rather than the riparian woodland and thickets where mountain beavers dig their burrows.

I've camera trapped this mountain beaver burrow almost seven months in the past 4 years, and the graph shows that golden mantled ground squirrels are not among its users.

I suspect the weasel killed the ground squirrel above ground and dragged it into the burrow to feed out of harms way. That's how weasels operate.

But as the graph shows, a weasel is more likely to encounter a mountain beaver in this burrow than a golden-mantled ground squirrel, and the chickarees and voles down there certainly run the risk of meeting this slinky grim reaper as well.

One other observation: the camera failed to record the resident juvenile and adult mountain beaver during the last sampling period. At least one mountain beaver has always been present.

Has the weasel appropriated this mountain beaver's underworld?

Is its nest now lined with the soft pelts of the previous residents?

I'll update you next month.

A chickaree shells a fir cone in the underworld earlier this month.

Reference:

King, C. 1989. The natural history of weasels and stoats. Cornell University Press, Ithaca.

One Month in Subterranea

This little movie is part of a continuing saga, a self-inflicted exercise in hope and frustration that started 4 summers ago when we found a collapsed mountain beaver tunnel in the northern Sierra Nevada.

In a strange way that narrow collapsed section of the tunnel resembled the shotgun-blasted stomach of Alexis St. Martin, the trapper whose misfortune set the stage for William Beaumont to become the grand old man of gastric physiology.

Like the gaping hole in St Martin's stomach, this mountain beaver's tunnel had a portal that exposed the mysteries within.

Collapsed mountain beaver burrows however are a dime a dozen.

What made this one special was that it opened up into an underground cavity big enough to accommodate a camera trap without blocking the passage.

Plus, this was not one of those thin-roofed sub-surface tunnels. This one was nearly 2 feet deep, making other cave-ins unlikely.

We started in 2010 by setting a still camera down there, a Sony s600 to be exact, and though there were lots of blank exposures the animal images were thrilling to see.

We learned that the mountain beaver's burrow system is a commons used by a lot of seldom-seen freeloaders like weasels, mink, and water shrews, not to mention great swarms of mosquitos.

Two summer's passed before I asked, "Why not video?"

It was an iffy idea, but I thought a few clips of the subway traffic would satisfy my whim and allow me to move on to other projects.

So I bought a home brewed DXG 567 from a fellow camtrapper and set it out in June, 2011 for the forthcoming workshop.

A bear cub unearthed the cam a couple weeks into the bargain, but not before the camera sampled some of the underground fauna.

In 2012 we tried again and discovered that chickarees actually mine the tunnels for truffles.

Now I was really hooked, even though the quality of the video schtunk.

The lens's field of view was too narrow, and depth of field was crumby.

So last winter I replaced the old lens with a $20 4mm wide angle lens from EBay.

The results are what you see above.

I am pleased with improved field of view, disgruntled with the focus, and flustrated with all the false exposures.

The camera is just too slow, and fixing it will be this winter's project.

My plan is to go back to the site and find all the entrances leading to that treasured tunnel.

If I can set external PIR sensors in the burrow entrances the camera will be rolling when the critters come cruising down the tunnel.

Video vision in the tunnel - Part 2

Our first attempt at subterranean video this year was disappointing.

Had the camera been placed differently the footage could have been better, but there was also the problem of the curious bear cub that dismantled the set.

The subterranean action however was more than enough to call us back.

Our second attempt in August was in a different segment of the same mountain beaver (=showtl) tunnel.

This time I came prepared with a customized mount that could be spiked into the hardpan on the floor of the tunnel and nailed into the log embedded in the silt bench above the tunnel.

Set 519.3 after being disguised
with a large flake of red fir.

The camera post was spiked and wired
to the embedded log. 

We covered the vertical hole with a large flitch of wood.

As you have seen in Part 2, the bear didn't show, and if any subterranean critters bumped into the camera they didn't move it.

















But I still didn't get the angle of the camera quite right. It should have been aimed up into the tunnel. The focus was also off, and the microphone made hideous sounds (which I'll try to remove -- sorry about that).

The camera in situ as we uncovered it
33 days later.

I just replaced the lens of the DXG 567v with a 4mm wide-angle CCTV lens, which will take in a much wider view.

We'll try again next spring.

Showtl's Underworld, Part 2

Six hours after we left, Showtl made its first appearance.  

What a difference a month can make during the growing season.

We bumbled about looking for the underground cams.

Alders in full leaf and knee-high grass covered the landmarks we expected, and we fell back on the GPS and Audrey's cognitive map to find the underground cameras.

But showtl didn't let us down.

Our rodent made almost daily appearances, which means the site was probably located near its nest.

Only 21% of 281 exposures however contained animals. The rest were blank images.

Normally we'd blame this on moving vegetation and phantom puffs of hot air which the infra-red sensor can't distinguish from animals, but this doesn't explain false exposures in the showtl's cool burrow.

It is more likely the rodent was zipping back and forth, and the camera was often too slow to get pictures of it.  

Despite false exposures, we still got 57 images of our quarry, and what you see here are the best. 

What you don't see are the two predators lurking in the tunnel.  

They're coming soon. 

The Showtl's Underworld

My obsession with showtls took a new turn this summer.

We attempted our first subterranean camera trap sets.

Two hours later two cameras were positioned to capture photos of the beastie in its underworld.

The showtl's tunnel was squarely in the middle of an alder thicket, and Montana Carl announced his intention to stay clear of alder, which he claimed had taken liberties with his person ever since the first day of the workshop.

In point of fact, springy alder limbs had been goosing all of us.

Making the sets therefore fell on the shoulders of the more agile young folk, while the two codgers sat on the sidelines to kibbitz.

The first task was to find the best location.

Several cave-ins had left gaping holes, much bigger than showtl burrows, that murmured of water and mosquitos within.

"Who's gonna stick their arm down there and take some pictures of the tunnel?"

Seabass volunteered.

The pictures showed us that the tunnel was anything but straight, and passed through a morass of buried timber and roots.

In some places it was an open trench. 

Next, we had to decide which cave-in gave the best subterranean perspective.

Snow water had created a small cavern immediately inside one of them.

It was an ideal situation for a camera trap: we could stake the camera and yield right-of-way to passing showtls.

Seabass drove a 1" pipe into the bed of the subway, and lowered the cam on its mount to just above the water.

The afternoon dragged on as we fine-tuned the camera's position, but we were all fluffed up with our cleverness, and for good measure we hurriedly staked a second camera down another chute.

Then we headed back to camp for a well-deserved happy hour.

Herman the Ermine was alurkin'

Herman the Ermine after cropping

"Study your photos carefully", is my codgerly counsel to novice camera trappers. "Its easy to miss the little guys."

As I gleefully reviewed Bill's showtl pictures the other day I failed to notice Herman the Ermine lurking in the background.

This afternoon Herman finally caught my eye.

Here's the uncropped photo, taken two and a half minutes before Showtl appears in its burrow.

Herman the Ermine before cropping

It could have been a close shave.

We've gotten three photos of weasels (long- and short-tails) in the North Yuba watershed, and they've all been in Aplodontia colonies.

This got me to wondering.

How does the showtl avoid or fend off fatal encounters with predators that can enter their burrows?

Does it have any anti-predator ploys?

You just don't see earth-blocked burrows in showtl colonies.

They don't have the pocket gopher's compulsive burrow-plugging habit which seems to hold many predators at bay.

In fact, from the number of burrow openings you'd think they had an open-door policy with weasels.

Here's a sketch of the burrow system and openings from Charles Camp's study of Aplodontia in 1916.

The strange reality is that showtl knows how to block burrows, but reserves the measure for its underground leaf and root pantries.

Camp wrote,

"A singular habit has been noticed in connection with the storage of food. In a burrow excavated at Point Reyes the entrances of two of the food storehouses were found plugged with large pellets of earth evidently manufactured by the animal for this purpose. These earthen balls were one to two inches in diameter and very hard and dry, evidently from being handled a good deal. It is curious that the outer burrow entrances are not similarly plugged." 

Here's a hypothesis.

Short sections of water-filled tunnels, a water seal of sorts, may bar weasels from entering the showtls nest cavity.

Camp didn't describe such water seals, but if we examined more burrows we might find that they exist.

The problem is that recreational burrow-diggers are hard to find these days.

But one thing is certain. The weasel that nails a showtl is well fed for several days.

An adult showtl outweighs an adult male long-tailed weasel by a factor of 3 or 4.

Herman the Ermine is 1/16th the size of the rodent, so the windfall of flesh would be much greater.

But do ermines take down showtls?

I suspect so, at least young ones.

An ermine is a fierce little killer, and if it can wrap its jaws around the showtl's throat the struggle would be brief.

Showtl emerged 2.5 minutes after Herman moved through

References

Camp, C.L. 1918. Excavations of burrows of the rodent Aplodontia, with observations on the habits of the animal. University of California Publications in Zoology, 17(18):517-536.

Spring cleaning

We descended on the alder thicket on the Yuba River back in June-- a band of eager camera trappers hungry for photos of the enigmatic but endearing showtl.

When it comes to camera trapping, showtl seems to be on the bashful side.

You have to wait a week or more before the adorable head with humanoid ears pokes out of the burrow.

But this time Bill Wilson got a nice series of showtl pictures over a period of two weeks.

This animal's watery burrow had an apron of knuckle sized rocks, and as you can see in these stitched photos, those rocks weren't washed out by water.

Showtl was doing its spring cleaning, while the plants were growing like crazy.

I wonder how much gold the showtls have unearthed since the 49ers?

Thanks Bill, for letting me show your catch.