Hungry Barred Owls Near Feeders
Over 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
Tracking 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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Two Songbirds And A Mouse
Two different kinds of signs — droppings and incisor marks – reveal the inhabitants of a woodshed during a very cold spell. The partially-eaten, shelled acorns have tiny grooves in them (difficult to see well in photo, my apologies), made by the incisors of a very small rodent, likely a White-footed Mouse or a Deer Mouse (the animals, much less their signs, are extremely difficult to tell apart, even if both species are sitting in front of you).
The two remaining signs are droppings from birds that sought shelter overnight inside the shed. Mourning Doves have very distinctive scat — individual round droppings, each about 1/4″ in diameter, consisting of coils of dark, solid waste which sometimes have a dollop of white uric acid on top.
The third and last sign is also bird droppings, but unlike the Mourning Dove’s, these are white and log-like. If you’ve been inundated with Dark-eyed Juncos this winter, you should be able to find these on the ground where they congregate.
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What Goes On Beneath Our Feet In Winter
It’s fairly unusual to see Deer or White-footed Mice, especially in the winter – they are nocturnal and they spend much of their time in the airspace under the snow next to the ground known as the subnivean layer. (A blanket of snow traps the earth’s heat, which melts the bottom of the snow, creating this layer of space.) Here both Deer Mice and White-footed Mice travel extensively, protected from both the cold (it stays within a degree or two of 32 F. regardless of outside temperature) and the eyes of predators. On cold winter days, groups including both species of mice keep warm by huddling in a common nest. (Photo of White-footed/Deer Mouse – extremely difficult to tell the difference by sight – by Alfred Balch.)
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Mouse Meals
Deer and White-footed Mice are viewed negatively due to their association with Deer, or Black-legged, Ticks, carriers of Lyme Disease. However, these mice are also beneficial, not only as a staple prey food for many predators, but as a vital contributor to the health of our forests.
Mice help spread various kinds of fungi by eating the fruiting bodies (which contain spores) and eventually excreting the spores. Certain fungi colonize the root system of trees, creating a symbiotic relationship called mycorrhizae. The fungus provides increased water and nutrient absorption capabilities to the tree while the tree provides the fungus with carbohydrates formed from photosynthesis. For many temperate forest trees, these fungi have been shown to be an essential element in order for them to prosper. By consuming fungi and dispersing their spores, these small rodents are inadvertently contributing to the vitality of our forests. (Note: look for the tiny incisor marks of mice in the devoured fungus.)
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Winter Mouse House
One of my very favorite animal signs is the winterized home of a Deer or White-footed Mouse. Most songbirds do not re-use their nests. Once the nestlings have fledged, what doesn’t get recycled directly from the nest by other birds or critters slowly disintegrates from rain and snow. That is, unless an agile mouse discovers it and renovates it first. Deer and White-footed Mice are known for using abandoned nests as larders (see https://naturallycuriouswithmaryholland.wordpress.com/2013/10/25/mice-preparing-for-winter/) or as homes for the winter. For the latter, a roof is constructed, usually out of milkweed or cattail fluff, but I have even found man-made insulation used as construction material for a roof. (The pictured nest has been well insulated with a roof of cattail fluff.)
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Nest Box Residents : Out With The Old, In With the New
In order to prevent disease or the passing on of parasites, it is a good idea to clean out nest boxes after they’ve been occupied. In the fall, after the last brood of eastern bluebirds or tree swallows has flown the coop, many nest box owners often clean them out in preparation for the next summer’s residents, but some wait until spring. This habit of waiting provides white-footed and deer mice (and occasionally flying squirrels) with a ready-made winter shelter and/or larder.
Feathers incorporated into the pictured grass nest indicate that tree swallows once occupied this nest box. After the last of the avian nestlings had fledged, mice moved into the box. After constructing a roof over the nest, the mice succeeded in renovating the former bird nursery into a winter mouse house. The remaining space inside the box served as a larder for nearby high-bush cranberries.
Unfortunately for the mice, but fortunately for the swallows or bluebirds that will reside here this summer, the responsible nest box owner dutifully cleaned out the nest box this spring, in accordance with avian-mammalian timeshare policies. (Thanks to Jim Lafley for the use of his photo.)
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Red Foxes Locating Prey
Deep snow certainly presents challenges to predators – their prey is well hidden for the most part, and if they are to survive, they must compensate for not being able to see what they are hunting. Foxes are an example of how a predator survives in a winter like the Northeast has had. A red fox hunting for food is constantly listening for the sound of rodent feet under the snow, and when it hears them (they can hear a mouse or vole three feet beneath the surface of the snow) they leap up into the air and pounce on or near their prey with their front feet. Most of the time they are not successful, and come up empty-mouthed, but they usually succeed often enough to survive. Biologists are still working on understanding exactly how they do this.
Researchers in Czechoslovakia, watching foxes hunt in the wild, determined that a fox’s success seems to correlate with the direction in which it jumps. If the observed foxes jumped to the northeast they killed on 73 % of their attacks. If they reversed direction and jumped exactly the opposite way, they killed 60 % of the time. But in all other directions — east, south, west, or variations thereof— they were successful only 18% of the time. Jaroslav Cerveny, the Czech researcher, feels that foxes have a “magnetic sense,” and are capable of lining up the rodent sounds that reach their ears with the slope of the Earth’s magnetic field, and when this occurs, dinner is usually caught. (This theory has yet to be confirmed, but the likelihood that it is correct is great.) (Photo by Susan Holland, in the wilds of northwest Ontario)
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Deer Mice And The Rigors of Winter
Even though Deer Mice are active year round, we don’t often see them, as they are active from dusk until dawn. During the winter, when it’s very cold, they commonly resort to short periods of torpor (4 to 9 hours) during the day to conserve energy. While torpid, their body temperature may fall to 55° F. from a normal temperature of 98°F.
When active, Deer Mice travel both under and on top of the snow. When travelling under the snow, they tunnel through it or use tunnels created by other small mammals. When travelling on top of the snow, their tracks, and often the drag mark from their tail, are evident. The pictured Deer Mouse was found curled up, frozen, at the end of a very lengthy trail of tracks and tunnels that ran over and through woods. Where the tracks began there was a slight depression in the snow (no tunnel, no tracks), indicating that the mouse might have fallen from the air after escaping from the talons of a bird of prey.
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Meadow Vole Tracks
Meadow voles and mice (white-footed and deer) leave most of the tiny tracks one sees on the surface of the snow. In deep snow, meadow voles tend to remain beneath the surface in tunnels, but occasionally do travel on top of the snow. Typically, a white-footed or deer mouse leaves a leaping, four-print pattern, often with a tail drag mark running between the sets of prints. A leaping meadow vole may or may not leave a tail mark and usually has paired prints. However, voles leave a variety of tracks patterns, depending on the speed at which they are traveling and the depth of the snow, so they can be confusing.
Although one might think that three different animals made the tracks in this photograph, every tunnel, track and hole was made by a meadow vole. The trail in the lower left was made by a trotting vole, the tunnel on the right was exposed because the layer of crust just under the new snow prevented the vole from going any deeper, and at the top, the vole was quickly bounding into the safety of its deeper tunnel.
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Contents of One Barred Owl’s Stomach
Fantastic guesses, given you had no measurements to work with. Very creative, indeed. Yesterday’s mystery photo was a packed version of the bodies displayed today.
Owls swallow small prey, such as mice and voles, whole, while larger prey is torn into smaller pieces before being swallowed. Once eaten, prey goes directly into the owl’s stomach, as owls have no crop, and thus no ability to store food for later consumption.
Like other birds, owls have a stomach with two chambers — one is the glandular stomach, or proventriculus, (yesterday’s mystery photo) which produces enzymes, acids and mucus and begins the process of digestion. (Because the acids are weak, only the soft tissues are digested.) The second stomach is the muscular stomach, or gizzard, also called the ventriculus. The gizzard lacks digestive glands – it serves as a filter, holding back bones, fur, teeth and feathers that are difficult to digest. The soft parts of the food are ground by the gizzard’s muscular contractions, and allowed to pass through to the rest of the digestive system.
Several hours after an owl has eaten, the indigestible parts remaining in the gizzard are compressed into a pellet the same shape as the gizzard. The pellet travels back to the proventriculs and remains there for up to ten hours before being regurgitated. Because the stored pellet partially blocks the owl’s digestive system, new prey cannot be swallowed until the pellet is ejected. If more than one prey is eaten within several hours, the remains are consolidated into one pellet. (In this case, one very large pellet!)
Update: I left the contents of the deceased Barred Owl’s proventriculus outside last night, and a resident Barred Owl recycled the Meadow Vole and Masked Shrew.
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