Going for shrew and bagging shrew

A chance encounter between two Trowbridge shrews (tentative id) 

Humbolt County, April 2013:


Question: Why don't camera trappers photograph more shrews?

Answer:  They aren't looking for schtinkin' shrews, because they aren't interested in shrews.

Who cares about little tiny ferocious mammals that eat 1.5 times their own weight a day in insects, spiders, centipedes, and worms?

Shrews may be one of the most abundant predators in woodland habitats, but it's their small size that makes them hard to photograph.

Camera trappers focus on the larger animals they know, and when camera traps are set for larger species shrews are usually undetectable.

Shrews live in a different time-space continuum, and I've photographed only a few by mistake.

They are usually a speck in the overall image, often partially hidden in leaf litter, and they are hard to identify. That's why most good pictures of shrews are nature-faked.

But they are intriguing subjects, and a few months ago I set a camera specifically for shrews.

I knew it might be a waste of time, but I staked the camera close to a rotting redwood log, and clawed away the surface litter, thinking the disturbance might attract a hungry shrew.

The batteries lasted 70 days, and there were 83 photos.

But only three pictures were of animals, and as far as I can tell, all were Trowbridge shrews with bald tails [yes, older shrews can lose their bicolored tail pattern to baldness].

The surprise was a pair of shrews having an altercation.

Going for shrew and bagging shrew may have been a stroke of good luck.

I'll have to repeat the exercise several more times to convince myself that I really know how to hunt shrew.

Canned shrew

Winter is a good time to find canned and bottled shrews.

Many walkers around here deem their daily communion with nature incomplete without the comfort of a brewski or two, and tossing the cans or bottles in the brush is apparently de rigeur.

Shrews are attracted to the containers at any time of year, but codgers can find them more easily in winter and redeem them for cash.

Nonetheless, it's been a coon's age since I've found a canned or bottled shrew.

So when I saw that can of Mickey's Malt Liquor tilted upward in the duff I went for it.

It had several ounces left in it, and I could tell there was something soggy in there too.

Sure enough, it was another Trowbridge shrew (Sorex trowbridgeii).

It was the right size and color, and the tail was bicolored, but in winter the wandering shrew (Sorex vagrans) looks quite similar.

The definitive identification had to wait until I could look at its 4 unicuspid teeth.

The photo doesn't do justice to the structure of the teeth, but it gives an idea of what you see under the dissecting scope.

Just keeping the wet shrew on the microscope stage while lifting the upper lip is a frustrating exercise, but that's what it takes to see the 4 diagnostic unicuspid teeth. Their relative size differs between species. The pigmented upper incisor is also slightly grooved.

Trowbridge and wandering shrews are the two common species I've found here.

Empty beer cans and bottles are not encyclopedias, but looking into them is a good way to learn about your local shrews.

Redeem them at your local recycling center, and you can actually get paid to learn about charismatic micro-mammals.

The Goose Pen

A goose pen with a circumference of 38 feet
can hold a lot of geese or sleep several loggers.

If you have seen one redwood you have NOT seen them all.

This old veteran was hidden in the brush and almost escaped our notice.

Standing 20 feet high, with a dbh (diameter at breast height) of 12 feet, it was one impressive stump and deserved thorough exploration.

I climbed down through a rent into the cavity 4 feet below the ground.

Several passages of differing size led to the outside through the charred walls, and internal recesses reached deeply into the roots.

This was one helluva place for a camera trap; so we climbed through the slash back to the truck and returned with the gear.

Then it started to rain.

The stump was not much of an umbrella; the camera case was soon wet, and the camera lens fogged immediately.

I tried drying it, but it was too dark to see what I was doing. I gave up and hoped for the best.

Before continuing our rounds, we interred some pieces of road killed squirrel into and under the old stump's walls.

Later that afternoon I told Lowell about the magnificent stump.

"You know what they call them up here?", he asked.

"Goose pens. The old timers used to pen up their geese in those stumps." 

The goose pen rewarded us with 107 photos of 9 species, and a success rate of 95%, which means there were few false triggers.

The deer mouse and wood rat of course were the first to show, but a hermit thrush appeared shortly after the alders dropped their leaves into the stump.

A Trowbridge shrew almost escaped my notice, but there it was, the voracious and fearsome midget mammal.

The brush rabbit's venture is a mystery. What was the attraction? It seemed a risky place considering the other visitors.

Of all the visitors, however, Fang the opossum spent the most time there (7 visits, 37 photos).

A bobcat paid three visits and left 11 images,

while a curious gray fox and a wet bear paused to examine the camera.

Though I like other images better, the shrew and the bear gave me the biggest thrill.

When I got home I realized I was missing my side cutting pliers.

You can see their blue handles under the bobcat's foot.

The blue plastic grips were all but missing when I recovered them.

There were rat nibble marks on the remaining traces of plastic, but the pliers still work.

Trowbridge shrew

I mistook this for a mouse, but on the computer screen at home it was clear that the ears were too small.

There are two species of shrews in the northern Sierra Nevada that sport brown summer coats and bi-colored tails.

The Wandering or Vagrant shrew (Sorex vagrans) prefers open meadows, while Trowbridge's shrew (Sorex trowbridgii) is found in conifer and mixed deciduous forests.

This hollow tree is in an extensive stand of red fir; so I am assuming we are looking at Trowbridge's shrew.

Shrews don't stay put, and they tend to be found in microhabitats overlooked by most camera trappers.

It's a special occasion when I get a photo of one.

A rocky recess

Camera set # 157: near Yuba Pass, Sierra County, California.

At the top of a large granite outcrop was a recess with a little pile of seed shells. That's where I set the camera.

Five weeks later there were 233 photos. The main visitor was a shadow chipmunk (68% of 84 photos). It paused there to eat fungi, gooseberries, and smaller seeds as early as 5:44 in the morning, and as late as 7:00PM. Its feeding station was well chosen, close to cover and protected from the eyes of predators.

Such a small patch of ground seems an unlikely path of travel, but there were other occasional passersby. Maybe the food scraps were the attraction.

A young golden-mantled ground squirrel made a few day visits, and a deer mouse made nocturnal visits.



On two nights a Trowbridge shrew passed by. One night the camera caught it examining the seed pile.



The place wasn't unknown to birds. A dark-eyed junco made two appearances.



But a blue grouse. perhaps a young hen was my favorite visitor. She stayed for 2 minutes scratching about for scraps from the chipmunk's table.

It's surprising how many small creatures visit such a small plot of ground.



Thanks to Craig Fiehler for bringing the seed pile to my attention at the end of the camera trapping workshop. It was too good to pass up.

Clapper rail

We decided to shoot down the Sacramento valley this week and stop at Point Reyes National Seashore to gather the three camera traps. My permit to camera trap there expires in January, and the redhead, who happens to be the spirit of Christmas in this family, suggested we do it now before things get too hectic.

Before heading down into the gulch, I vowed to pull the cams without pausing to view the pics.

Normally the redhead watches me with binoculars from the road, and radios the whereabouts of elk. This has attracted park visitors who ask, "Any good birds today?" or "Have you seen any elk?" Usually she signals me as they approach, and I duck out of sight like a commando.



There was only one lone bull elk in the area, and when it disappeared into the next gulch, she informed me she was retiring to the car to read.

Finding the first camera was a workout. The GPS told me I was on top of it, but it took me 15 minutes to find it 6 feet away on the other side of the thicket. It took more time to pussy-foot my way to the other camera sets, because the rains have turned the bottom of the gulch into a quagmire, and the elk have churned it up like water buffalo in a rice padi. It took a full hour and a half to collect the cams and posts.

After dinner I downloaded the pictures, and the big surprise was the clapper rail. This is actually the California clapper rail, an endangered subspecies from the San Franciso bay area.

The bird visited this muddy drainage site a week ago at 4:10 in the afternoon. This was a new camera trap set I made during my last visit over 6 weeks ago, and it was also my final desperate attempt to get more pictures of mountain beavers. (The wiley rodents seemed to have disappeared from their haunts where I photographed them back in July. More about them in a few days.)

The location is a waterlogged thicket at the base of a steep hill. I don't think this is the kind of place a birder would look for rails. Nearby in Abbott's lagoon and the backwaters of Drake's Estero there is more typical marshy habitat, but there is plenty of cover here, and the soil is deep and wet.

The only other avian visitor was a hermit thrush.



Rails feed mainly on invertebrates they probe from the mud, but small vertebrates like this shrew are said to be fair game. (See the velvety gray hair and bicolored tail -- it's another Sorex trowbridgeii.)



These were lucky pictures, because the camera is set for night time shots. Dim overcast lighting and shade had fooled the camera into thinking it was night. In five months of camera trapping this gulch, this is the only rail captured by the cameras. I am pleased.