From the Contact Station April 2022

Little Furry Things

I recently read an article in Cool Green Science, an e-publication by Nature Conservancy, by science writer Christine Peterson. She described the life of a Deer Mouse, North America’s most abundant mammal. It is both predator and prey and widely adapts to many habitats. It got me thinking about seldom seen critters on the Refuge. — Warning, before you proceed, this article has some icky factor to it. — Indeed, best viewings of these kinds of animals seem to be in the clutches of talons, a large bill or toothed mouth amply demonstrated in photo contest submissions we get. I spent a slow afternoon at the contact station several years ago, watching a Great Blue Heron stalking prey in the field behind our building. They are amazing to watch; what patience. My Great Blue struck and snagged a small furry critter. It spent some time “massaging” it in its bill as it moved it to headfirst position, finally swallowing it whole. It was not over quickly. I could see the lump in the long neck as the heron moved it down. And then the lump moved upward, then the heron again performed some maneuvers with its neck. It was back and forth a couple of times, until the heron seemed satisfied and the lump was gone. The heron moved on a couple steps. It was just in time to snag a second furry critter. I was wondering where it was going to put that one but decided not to watch the process again.

Talking to our biologist Alex recently, I asked about the furry critters on the refuge. There is a big population of Townsend’s Mole throughout the Refuge. That is not surprising considering its favored habitat is the subsurface domain of river floodplains, meadows, hayfields, pastures, and residential lawns. But Townsends Moles, Scapanus townsendii, are almost exclusively fossorial. That means it is adapted to digging and lives primarily, but not solely, underground. They do come out at night sometimes, to mate or to disperse to new territory. By staying underground, they are less likely to be preyed upon. Their main predator is Barn Owls, along with other owls which all hunt at night of course. Carnivores such as coyotes and weasels will also prey on them. (See critter spotlight for more details on the Townsend’s Mole.)

So, what other candidates are there for being predator food. Well, way too numerous to count, but keeping to the furry kind: mice, shrews and voles are good candidates. Mice are thigmophilic, which means they like making contact with surfaces. They move along walls or are move likely to travel through brush and grass tunnels. Voles, even though they tunnel, tend to be active in open land making them quite vulnerable to our hunters.

Voles are sometimes known as meadow mice or field mice. The average life of a smaller vole species is three to six months. They become adults in one month and can have five to ten litters in a year of three or four pups, if they make it that long; two litters are the norm. Gestation lasts for three weeks, and the young voles reach sexual maturity in a month. Breeding season is generally from March to September, providing ample food for our eagles, hawks, coyotes and (as seen in the photo) falcons. Our voles include Creeping (Oregon) Vole and Townsend’s Vole. (note: Townsend collected specimen to describe a number of small furry animals in the 1830s, hence several species carry his name.)

We have Deer Mice and Pacific Jumping Mice on our Refuge list. Mice have a shorter gestation period than voles, averaging 10-20 days, with anywhere from 5-15 babies. Despite the predation success, given these reproduction rates, the population can thrive. It is an interesting contrast to the mole’s life cycle.

Shrews can be found on the refuge, with Dusky Shrew and Vagrant Shrew being the species here. Although its external appearance is generally that of a long-nosed mouse, a shrew is not a rodent, as mice are. It is a close relative of hedgehogs and moles. Shrews have sharp, spike-like teeth, whereas rodents have gnawing front incisor teeth. Shrews will reuse the tunnels made by moles and voles. They forage for seeds, insects, nuts, slugs, small animals, seeds, roots and worms.

Some keys to telling voles, shrews and mice apart are voles have short tails, while mice have long tails (about their body length). Voles also look heavier than mice, while mice are long and skinny to go through tighter spaces. On voles, the rounded ears and eyes are small, while mice have big, rounded ears and large, easily seen eyes. A shrew has a pointed snout, but unlike the mole, a shrew’s front feet are not enlarged. Also, a shrew’s eyes are tiny, but they are visible in most species.

So, see if you can spot and identify a small furry critter the next time you are on the refuge. They are much more abundant that we think, just really hard to find because they have perfected their hiding habits and when we do see them, well, it might just be parts.

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Critter Spotlight: Townsend’s Mole, Scapanus townsendii

Townsend’s moles excavate a permanent tunnel system to move around their territory and find earthworms, their favored food, and insects that have fallen into the tunnels. The tunnels are about six to eight inches underground, with some shallower feeding tunnels. And, yes, they are responsible for those little mounds of dirt in your lawn. They also like to nibble plant tubers and bulbs occasionally.

Because their underground habits provide safety from many predators, they don’t have to be a prolific breeder to maintain their population like other furry critters of the refuge. They breed once per year between November and February, giving birth to an average of three offspring per litter. Young moles are born in late March or early April, about four to six weeks after mating.

Townsend’s Mole uses its sense of touch to move around the tunnels. It has sensitive vibrissae on its snout to perceive its surroundings. Its highly reduced eyes only detect light intensity and not individual shapes. The senses of smell and hearing are secondary. Chemical cues are used to mark territories and indicate mating availability. Other adaptations for fossorial life are a cylindrical and streamlined body and fur that is short and able to bend easily in any direction. Perhaps the greatest digging adaptation of this species is its broad shovel-like front forepaws. They are as wide as they are long, and the digits have large claws. The pectoral girdle that supports the front limbs allows the limbs to rotate ventrally for more efficient digging. The humerus is broad and square-shaped and it articulates with the clavicle. Its hindfeet are much smaller and have shorter claws. Its tail is short and mostly naked, being sparsely covered with course hairs.

Since the lowland habitats can often be prone to seasonal flooding. They will burrow ahead of flood waters until they are forced above ground by the water. Being proficient swimmers, they can also sometimes swim to higher ground. Flooding often kills many moles, but those that survive are usually able to quickly return to their territories once the waters recede. Having watched our atmospheric rivers flood many of the fields this last year, it is likely there was a lot of territory shifting or individual loss of our moles. High quality habitat is often agricultural fields which are fertilized with solid manure. These areas generally have abundant earthworm populations. I am sure our summer grazing cattle contribute to the fertilizer load, although cattle can step into tunnels crushing moles on occasion.

There are benefits to having Townsend’s Moles in our Refuge. They influence many aspects of the local environment: decomposition, fertilization, physical structure, and hydrology. The impact of Townsend’s Mole on the soil ecosystem is significant. They mix and aerate the soil as they move around. The extensive tunnel systems act as communal runways for many other mammals including voles, mice, shrews and occasionally ground squirrels, and gophers.

As a major predator in its subterranean environment, it eats a substantial biomass of soil-dwelling invertebrates and ecosystem components. Their predator pressure on insect larvae and earthworms helps to keep these populations in check. As prey, the mole is a minority food source for some predators.

Did You Know?:

1. The creeping vole, Microtus oregoniis, is a fast animal. It can run up to 6 mph.
2. (Well, not so fun for the moles.) Historically, mole skins were extensively marketed. Throughout the 17th, 18th, and 19th centuries. They were used for capes, trimmings, purses, and tobacco pouches.

-Susan Setterberg, Contact Station Volunteer