An online resource based on the award-winning nature guide

Meadow Vole

Hungry Barred Owls Near Feeders

3-4-19 barred owl _U1A2992Over the past few weeks many people in northern New England have discovered Barred Owls perching near their bird feeders during the day. At this time of year, with snow on the ground, food is harder to find and owls are forced to hunt during the day as well as at night. Bird feeders are a sure source of food, as mice and voles are coming out to feed on spilled seed (most often at night).

The owls we see are relying primarily on their sense of hearing to locate small rodents. Their ear openings are asymmetrically placed, which means that sounds reach the owl’s ears at different times. This helps them zero in on the exact location where the sound is coming from, both when they are perched as well as in flight.

Although Barred Owls can detect the sound of a mouse scurrying through tunnels two feet beneath the snow, this winter has been more challenging for them than many. Almost every snow storm has been followed by rain, which has created multiple layers of icy crust. Although sound may be heard through solid, liquid, or gaseous matter, one wonders if these multiple layers of crust compromise an owl’s ability to hear. In addition, these conditions can’t help but impede an owl’s ability to reach its target as quickly as it normally does.

A dear friend whose compassion for creatures big and small is unmatched was going to great lengths (coating balls of hamburger with hair cut from her dog’s coat so they would bear some resemblance to small rodents) to help a resident owl in a time of need. Some would argue that nature shouldn’t be interfered with, but those readers with a desire to come to the aid of a hungry owl could let a little seed fall on the snow that’s packed down around the feeder in hopes that a large supply of accessible food might attract more rodents which might fill more owl stomachs.

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Meadow Vole Tracks & Tunnels

2-4-19 meadow vole_U1A2759Tracking animals can be an elusive endeavor because so many things can alter the condition of the tracks. Have recent flurries erased the details of an imprint? Has the sun melted and enlarged a track? Was every toe registering? Did wind-blown snow cause the tracks to vanish into thin air? Was the animal walking, loping or tunneling or a combination of all three?

The reason you use more than just one track to gather information, such as the stride of the animal and the width of its trail, is that sometimes the individual tracks defy the hard and fast rules of some tracking guides. A commonly accepted generality is that Deer and White-footed Mouse tails leave drag marks, and Meadow Voles’ shorter tails don’t. However, in the right conditions, even a vole’s one-inch tail can drag (see photo), though not creating as long a line as a mouse’s tail would. The Meadow Vole whose tracks are in this photograph was loping along when it suddenly decided to seek cover under the snow and began to (try to) tunnel. Perhaps a predator instigated this behavior.

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Track Stories

1-9-19 coyote gets vole_u1a8956Finally – a snowstorm not followed by rain! Tracking has been challenging, to say the least, this winter in central Vermont. However, 36 hours after the latest snowstorm, there was a plethora of track stories to read in the snow. A ruler or measuring tape and a good field guide to tracks (Mammal Tracks & Sign by Mark Elbroch and Tracking & The Art of Seeing by Paul Rezendes come to mind for indoor resources, and the smaller Mammal Tracks and Scat: Life-Size Pocket Guide by Lynn Levine for keeping in your backpack) will allow you to determine who’s been where and what they’ve been up to. Signs of feeding, marking and seeking shelter are just a few of the things these stories reveal.

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Snow Stories Begin

1-5-18 owl print in snow - Rob Foote IMG_4571 (002)

With snow on the ground, the season of stories in the snow has begun. Many of the animals that remain active in New England during the winter are nocturnal so we rarely get a glimpse of them. But, more than at any other time of year, we are privilege to their activities due to the tracks and traces they leave in and on the snow during the night.

Much information can be gathered from these signs. Often at a kill site, the identity of the predator as well as the prey can be determined by shape, form or measurement. One can see from this photograph that a bird of prey (measurements indicate a barred owl) swooped down on a small rodent (judging from tracks, probably a meadow vole) and was successful in capturing it.

Even though a kill scene such as this, or any other wildlife activity recorded in the snow, may reveal the probable identity of the characters in the story, there are always more questions than answers, which is what gets us out in this frigid weather, day after day. The main question I’m left with after viewing this scene is why do voles and mice risk their lives by travelling on the surface of the snow at times, when they just as well could have covered the same ground in the maze of tunnels they’ve created deep in the subnivean layer between the ground and the snow (where they would be out of sight of hungry predators)? (Thanks to Rob Foote for photo.)

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Tunnel Vents

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Frequently you find a hole about an inch wide in the snow in the middle of a field, with no tracks going in or coming out of it. Logic tells you it leads to the subnivean layer – where the snow, warmed by the ground, sublimates into water vapor, creating a small space between the surface of the ground and the snow where the temperatures is relatively stable at 32 F. It is here that small rodents such as mice and voles create a maze of tunnels through which they travel from their sleeping quarters to feeding stations, undetected by many predators.

However, the lack of tracks into and out of this hole indicates that it is not an exit or entrance to the subnivean layer, but rather, it is a vent leading from the subnivean tunnels to the surface of the snow. Carbon dioxide from animal respiration as well as carbon dioxide released from the ground builds up to an unhealthy level in these tunnels. The holes we see in the snow are ventilation shafts, allowing the carbon dioxide to escape from the tunnels. The formation of crystals around the edge of the pictured vent indicates that warm, moist air from rodent lungs is rising up out of it.

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Puzzling Kill Site

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Close examination of the bits of fur scattered over a 15-inch-diameter patch of snow reveals that the animal to whom the fur belonged was very small and would have appeared brown to an observer. (The hairs are black, but they have a brown tip.) This eliminates gray/black shrews and moles, leaving a white-footed mouse (due to habitat) or a species of vole (most likely meadow vole) as the victim. Striped skunk tracks led to the remains of this rodent, which is not surprising, as mice (Peromyscus sp.) and voles (Microtus sp.) are high on their list of preferred vertebrates. What is puzzling is why the fur wasn’t consumed and why so many of the internal organs (top of photo) were among the discarded fur. A skunk would neither skin nor eviscerate its prey. Explanations welcome!

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Meadow Voles Soon To Begin Breeding

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Under perfect conditions, with no predators, no deaths and abundant food, a pair of meadow voles (Microtus pennsylvanicus) could produce a million descendants in a single year. Because they are prey for nearly every meat-eating animal that exists, however, their population, while large, is nowhere near this.

Even though the number of meadow voles is relatively high and they are active day and night, year round, it is unusual to actually set eyes on one. What we do find, especially this time of year, are meadow vole signs in the snow: mazes of runways on the surface of the ground that are exposed as snow starts to melt, air-exchange holes originating in their tunnels and extending to the surface of the snow, tracks and entrance/exit holes to their tunnels.

The social behavior of meadow voles is about to undergo a seasonal change. During the winter, when they are not breeding, meadow voles are more social and commonly share their nests, probably to conserve heat. In another month, however, as breeding begins, females become fiercely territorial towards other females, and males are aggressively establishing dominance over each other. The peaceable subnivean meadow vole kingdom is about to come to an end. (Thanks to Susan and Dean Greenberg for photo op.)

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.