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Predator-Prey

Barred Owl Story in the Snow

2-17-14  barred owl prints 013These beautiful impressions in the snow tell the story of a Barred Owl diving feet first after prey, most likely a vole or mouse. The fact that there are no rodent tracks on the surface of the snow tells you that the mouse or vole was well hidden in its tunnel under the snow at the time. Apparently the owl’s talons did not reach their target (at least, no blood or rodent remnants), and the owl continued to plow through the snow in repeated attempts to capture its prey before taking flight.

The presence of facial discs (feathers in the shape of a funnel around each eye that direct sound waves towards the owl’s ear) plus the differing size and asymmetrical placement of an owl’s ear openings allow the owl to discern the direction a sound is coming from, how far away it is and its height relative to the owl – even in the dark or under the snow! The exceptional hearing ability of owls, particularly those in the genus Strix (which includes Barred and Great Gray Owls), enables them to plunge into the snow and often successfully capture prey, sight unseen. (Species of owl was determined by wing length. Thanks to Rob Anderegg and Jennifer Grant for photo op.)

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Hide & Seek: Voles & Foxes

1-9-14  hide and seek-fox & vole IMG_2735Unlike wolves, which hunt in packs and often take down prey larger than themselves, red foxes are solitary hunters and as a result often catch prey much smaller than themselves, such as mice and voles. During the winter, mice and voles become more active during daylight hours because much of their time is spent under the snow, where they remain hidden from view. Consequently, in winter you’re more likely to see a fox hunting during the day than in the summer. Whenever it’s hunting, night or day, a fox depends heavily on its acute sense of hearing. It is most sensitive to lower noises such as the rustling and gnawing sounds that small animals make as they move through vegetation or feed on seeds, buds and twigs. Foxes can locate these sounds several feet away, to within inches of their true location, under three feet of snow. Recent research suggests that they may also use the magnetic field to help them locate prey. (photo: red fox & meadow vole tracks)

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The Butcher Bird

1-3-14 impaled mouse & MS shrike by Bridie McGreavy DSC_0146The Northern Shrike (Lanius excubitor) is highly unusual in that it is a predatory songbird. Birds, mammals and insects are preferred over nectar, nuts and seeds. This tundra-nesting bird comes as far south as New England to overwinter, where it preys mainly on mice, voles and small birds. The Northern Shrike often kills more prey than it can immediately eat or feed its young, storing the excess food to eat later, when available living prey may be scarce. The manner in which it stores this extra food is what gave it the name “butcher bird;” it often impales prey on a thorn, broken branch (as in photograph) or even barbed wire, or it wedges prey into narrow V-shaped forks of branches, where they hang until reclaimed by the shrike. (Impaled mouse photo by Bridie McGreavy; northern shrike photo by MS Henszey)

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Northern Hawk Owl

n. hawk owl3- 231The Northern Hawk Owl is a bird of the remote Alaskan and Canadian boreal forests. Its name reflects the fact that this diurnal owl has both the appearance and behavior of a hawk, specifically, an accipiter. Although the Northern Hawk Owl winters throughout its breeding range, it periodically erupts southward into southern Canada and the northern United States. Sightings of this bird are rare in Vermont, but in recent winters, including the current one, there have been some. As with Snowy Owls, the magnitude and extent of these winter irruptions are thought to correlate with high reproductive success followed by severe winter conditions and decreased prey availability, but much remains to be understood about their winter dispersal habits. What we do know is that the Northern Hawk Owl’s skills as a hunter are very impressive. It can detect prey (small rodents, grouse, hares) by sight at a distance of half a mile and just using its ears can find prey under a foot of snow.

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Weasel Tracks

12-24-13 weasel & stonewall IMG_9602When looking for signs of weasel– Long-tailed or Ermine (formerly called Short-tailed Weasel) – in winter, stonewalls are a good place to head. Both of these nocturnal mustelids prey on small rodents such as mice and voles, which frequent the nooks and crannies of stonewalls. In winter weasels cover a lot of ground looking for prey – the home range of an Ermine is between 30 and 40 square acres, but when food is scarce, they may travel two or three miles in one night. Often their tracks will run the length of a stonewall on one side and then back the other side. Intermittent pauses are made as the Ermine stands on its hind feet and stretches its neck out, searching the landscape for both movement and sound.

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Interpreting a Kill Site

12-18-13 hawk kill IMG_4136When there’s snow on the ground and you come upon a site where a predator successfully caught prey, there are usually signs that will help you determine who the main players were. In the above scene, remnants of red squirrel fur confirm the identity of the prey. If you look at the top of the image, you can make out a faint wing impression. Although not in this case, both wings of an avian predator often touch the surface of the snow, allowing you to measure the wingspread, and this information can help to eliminate some species of raptors. Birds of prey often defecate at a kill site. In the lower left corner of the photograph, as well as to the left and right of the packed area where the squirrel was eaten, you can see white (uric acid) bird droppings. Given that it is a hawk or an owl, knowledge about their respective evacuation habits will allow you to narrow down the possibilities even further. Owls tend to let their droppings do just that – drop, leaving small plops on the ground. Hawks, on the other hand, tend to forcefully eject their droppings some distance away. The long, thin streaks at this site were definitely propelled outwards, making it likely that the predator was a hawk. Familiarity with the hawks that overwinter in your area can help pinpoint which species it could be.

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Canada Lynx “Snowshoes”

12-16-13 lynx & bobcat feet IMG_3811Bobcats and Canada Lynx are in the same genus, and are roughly the same size (averaging 15 to 35 pounds), with Bobcats usually weighing a bit more than Lynx. The size of their feet is vastly different, however, and not proportional to their relative weights. A Lynx has much larger feet and longer legs than a Bobcat. Its range extends further north, which means it must be well equipped to deal with snow much of the year. A Lynx has big, furry paws, and when its feet land the toes spread way out. Both of these adaptations help a Lynx’s feet act like snowshoes, helping it to chase down food in the winter. Much of the time, this food consists of Snowshoe Hares –anywhere from 60 to 90 percent of the diet of Lynx is made up of hares. The soles of Snowshoe Hare feet are also well-furred, particularly in winter, enabling them to run on soft, deep snow without sinking in very far. Because Snowshoe Hares are extremely fast and agile (reaching speeds of 30 mph and jumping 12 feet in a single bound), the feet of any serious predator must also be well adapted to traveling on snow.

Note: Bobcat sightings are much more frequent than Lynx in northern New England (the southern tip of the Lynx’s range) but breeding populations of Lynx have been documented in the last two years in the boreal forests of Maine, New Hampshire and Vermont.

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Eastern Chipmunks “Clucking”

10-2-13 eastern chipmunkIMG_3035Especially in the fall, and sometimes in the spring, the woods are full of “clucking” Eastern Chipmunks. It’s unusual to hear this call during the summer, but once leaves have started to fall off the trees, giving chipmunks a clearer view of the sky, the chorus begins. One chipmunk starts calling, and the message is passed on to other relatives, who join in. These vocal little rodents are warning each other of the presence of an aerial predator, perhaps a hawk or day-hunting owl. The next time you hear this distinctive alarm call, look skyward. You may well be rewarded with the sight of a raptor flying overhead.

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Cerceris fumipennis: a biosurveillance tool for the emerald ash borer

8-19-13 Cerceris wasp with beetle prey2 099While we’re more familiar with social wasps, such as paper wasps, yellow jackets and hornets, there are also parasitic and solitary wasps. Solitary wasps live alone (as their name implies), all the females (not just the queen) are fertile and they are predatory. Among them is a wasp, Cerceris fumipennis, which preys exclusively on the family of beetles (Buprestidae) to which the Emerald Ash Borer (EAB), the invasive beetle that’s threatening the ash tree population, belongs. After catching and paralyzing its prey, the wasp carries it back to her larvae in the nest she’s dug underground. A biosurveillance program exists which involves monitoring the prey that this species of wasp collects and brings back to the nest, in order to detect the presence of the Emerald Ash Borer in any given area. (This is how the EAB was first detected in Connecticut.) Pictured is a Cerceris fumipennis wasp with a Buprestid beetle (not an EAB) prey. (To become involved in Vermont’s citizen science biosurveillance program next summer, contact entomologist Trish Hanson of the Vermont Dept. of Forests, Parks and Recreation at Hanson.Trish@state.vt.us .)

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Woodland Jumping Mouse Succumbs

8-13-13  woodland jumping mouse134Usually animals that have been killed don’t last long enough for humans to discover them unless the human disturbs the predator right after it’s killed its prey. This may well have been the case when I came upon this Woodland Jumping Mouse. It is actually fairly unusual to set eyes on a jumping mouse, dead or alive, as they are quite secretive. This remarkable one-ounce rodent has long hind feet and a distinctly long tail, which makes up more than half of its total length of eight to ten inches. Using its hind limbs for propulsion and its tail for balance, the Woodland Jumping Mouse is able to make large leaps of up to eight feet or more to escape danger. (More often it walks around on all fours, or uses short hops for greater speed.) Another survival strategy that jumping mice use is to remain motionless for up to several hours, relying on their coloration and cover for protection. Apparently neither adaptive behavior was effective enough to spare this mouse’s life.

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Backswimmers

Backswimmers are aquatic insects that seek out prey as large as tadpoles and small fish. They row around ponds with their fringed hind legs and grasp prey with their front pair of legs. The piercing mouthparts that they use to kill their prey are also capable of giving humans who handle them carelessly a nasty bite (they are also known as “water wasps” for this reason).7-12-13  backswimmer 376 Because they spend most of their time on their back, their coloring is opposite that of most insects – backswimmers typically have a dark belly and a light-colored back, making them less conspicuous to predators (and prey) both above and beneath them. These tiny bugs can stay submerged for hours thanks to their ability to store air bubbles in two channels on their abdomen which are covered with inward-facing hairs. Backswimmers are often confused with Water Boatmen, which are not predaceous, do not bite, and swim “right side up.” Water Boatmen’s dark color and parallel lines on their backs help distinguish them from Backswimmers.


Common Loon Chick Meal Delivery

7-10-13 loon chick being fed 119For the first few days of a loon chick’s life, both of its parents are ever-present, catching and delivering small fish, crayfish and invertebrates for their one or two chicks. Their initial buoyancy and their lack of experience prevent the chicks from procuring their own food for the first month or so, although they soon learn how to chase fish. During the first couple of weeks, the parent loon, having caught a crayfish, small fish or other prey, swims right up to its young and offers the chick its next meal. The chick grasps the food while it is still in its parent’s beak. The parent lets go, and the chick attempts to swallow the crayfish (in this case). In the beginning, the chick often drops its meal. The parent then dives down to retrieve it and once again offers the same crayfish to the chick. This sequence of events can happen over and over until the chick finally manages to hold onto and shift the crayfish into a head-first position in order to swallow it. By the third week this beak-to-beak service begins to be replaced by a practice designed to teach the chick how to capture its own meals. The parents start dropping the food they’ve caught for their chick into the water in front of them, forcing the chick to dive and develop the skills necessary for survival. (The pictured loon chick is well into its second week. Close examination reveals that the chick’s “egg tooth,” used to exit the egg, is still present at the tip of its beak. By week #3 it is not evident.)


Dragonfly Eyes

7-8-13 dragonfly eyes2 381Dragonflies (and bees) have the largest compound eyes of any insect, each containing up to 30,000 facets, or ommatidia (house flies have 6,000). Each facet points in a slightly different direction and creates its own image, and the dragonfly’s brain compiles these thousands of images into one picture. This eye structure enables dragonflies to be extremely sensitive to motion. Because a dragonfly’s eyes wrap around its head, it can see in all directions at the same time (though its forward-looking vision is the sharpest). When capturing prey, a dragonfly doesn’t chase it – it intercepts it in mid-air, and it’s successful nearly 95% of the time. This hunting technique entails calculating the distance of its prey, the direction it’s moving and the speed that it’s flying – an impressive feat any tennis, baseball or football player would especially appreciate!

(Photo is looking down on the eyes of a Common Green Darner. Three simple eyes, or ocelli, are located in the black section below (above in the photo) its two tan compound eyes. The short, thin black lines are its antennae, which can detect wind direction and speed. The yellow section is part of the upper half of its face, or frons.)


Moth Eyes and Biomimicry

7-1-13 luna eyes 020Because moths need to use every little bit of light available in order to see in the dark, their eyes are highly non-reflective. (This is also helpful in decreasing the chances of predators spotting them.) Scientists, through biomimicry, have come up with a number of technological advances, including the development of a film that can be applied to solar cells which helps keep sunlight from being reflected off of them before the light can be utilized. Man-made materials based on the structure of moth eyes could someday reduce the radiation dosages received by patients getting x-rayed, while improving the resolution of the resulting images. Research on recreating the pattern found on moths’ eyes onto plastic could lead to reflection and glare-free display screens for televisions, cell phones, computer monitors, eyeglasses, speedometers and more.


Damselflies Hunting

6-12-13 damselfly eating prey2 147Damselflies, nature’s more delicate version of a dragonfly, spend most of their life underwater, first as an egg and then as a nymph. Eventually, after a year or so, they crawl out of the water onto nearby vegetation, shed their nymphal skin for the final time and emerge as winged adults. A damselfly’s beauty belies its behavior — most damselflies are voracious predators, both as aquatic nymphs as well as adults. In flight, they hold their bristly hind legs in a basket shape to scoop up their prey. The prey is then transferred to their front legs, which hold it while the damselfly devours it.


Six- and Twelve-spotted Tiger Beetles Active

4-25-13 6 and 12-spotted tiger beetlesTiger beetles (named for their ferocity) can be easily recognized by their quick, jerky movements, huge eyes and large, multiple mandibles. Look for these voracious hunters in sunny, open spots where they can easily spot prey and potential predators. The six-spotted tiger beetle is hard to miss, thanks to its iridescent green outer wings, or elytra. Contrary to that which its name implies, this species can have five, two or even no white spots. It is most likely to be found on exposed rocks, logs and tree trunks, whereas the twelve-spotted (may have 12 or fewer spots) tiger beetle tends to prefer moist sandy spots. They both capture and liquefy their prey by masticating it with their formidable mandibles, squeezing it and swallowing the juice. Both of these species of tiger beetles have a two year life cycle, overwintering as adults their first winter, emerging early in the spring, mating and laying eggs during the summer and then overwintering as larvae.


Foraging Technique of American Robins

4-17-13 A. robin2 IMG_8800In the fall and winter, fruit makes up about 90% of an American robin’s diet. In the spring, only 10% of a robin’s diet consists of fruit; invertebrates make up the remaining 90%. (Summer is a fairly even mixture of both.) At this time of year, earthworms are a popular food item with robins. Watching a robin foraging for a worm can make you wonder whether the robin is using its ears or its eyes to locate the worm. It turns out that most worms are seen, not heard, by robins. Because the sound of worms burrowing in the soil is of low intensity, they usually cannot be heard by robins because of background noise. Using sight, not sound, the robin first aims one eye toward a spot on the ground in front of it, and after holding this position for a few seconds, rotates its head and draws a bead with its other eye on the same spot– an earthworm in its burrow. The robin then quickly thrusts its bill into the burrow in an attempt to get its next meal.


Killdeer Distracts Predator by Feigning Injury

4-15-13 killdeer IMG_8336

Killdeer arrived back in northern New England last month and have already begun nesting. Being a ground nester, the killdeer has many mammalian predators from which it needs to protect its eggs, including weasels, skunks, opossums and raccoons. Nesting killdeer have a number of responses to predators, which include several different types of distraction displays which draw attention to the bird away from its nest. One of the most common displays is to feign injury by assuming a position which makes the bird appear vulnerable. When a predator approaches, the bird runs away from the nest, crouches with its head low, wings drooping and tail fanned and dragging the ground to display its rufous rump-patch. The predator typically follows, seeing an easy meal, and as soon as it gets too close for the killdeer’s comfort, the killdeer continues to lead it off by alternate flights and sprints.


Common Raven Defends Nesting Territory

4-5-13 raven chasing red-tail2 IMG_8693Common ravens are known for their aerial acrobatics, often doing rolls and somersaults and other amazing tricks.  According to Cornell Lab of Ornithology, one bird was seen flying upside down for more than a half-mile. Young birds are fond of playing games with sticks, repeatedly dropping them and then diving to catch them in mid-air.  The pictured raven, however, was much too busy to be doing cartwheels in the sky.  It has a nest with eggs nearby, and during its morning patrol encountered a red-tailed hawk which it drove out of sight in a matter of seconds.  Although small mammals make up most of a red-tail’s diet, they are known to also prey on smaller birds, including defenseless nestlings, which the ravens will have in the next few weeks. (Because of the angle, the  24-inch-long, 53-inch-wingspread raven looks disproportionally larger than the 19-inch-long, 49-inch wingspread red-tail.)


Mourning Dove Remains

3-13-13 mourning dove remains IMG_5958A cooper’s hawk made short work of a mourning dove near my bird feeder recently, killing and apparently, given the large number of feathers scattered on the snow, plucking the dove on a nearby snow bank. If you look closely you can see whole sunflower seeds in amongst the feathers. These came from inside the mourning dove’s crop. Mourning doves generally feed quickly, filling their crop with seeds which they digest later, when they’ve found a safe spot in which to roost. Unfortunately for this particular dove, it didn’t live long enough to have that opportunity.


Coyotes and Beavers

3-12-13 coyote & beaver lodge2 IMG_6223A study of coyote prey (through stomach contents) in the Adirondack Mountains of New York revealed that beavers were second only to white-tailed deer. This photograph shows that, possibly for the last time this winter, a coyote recently took advantage of a still-frozen-but-fast-thawing pond by walking across it in an attempt to reach an active beaver lodge. Once there the coyote attempted to dig into it in order to reach the inhabitants. A hard, two-to three-foot-thick wall of frozen mud, logs and sticks kept the beavers well protected, as it was designed to.


More Otter Sign

3-1-13 crayfish IMG_3205It’s often a lot easier to find signs of otters than otters themselves. Recently I discovered two dead crayfish on the shore of a mostly iced-over pond that I knew was inhabited by otters. Nearby otter scat confirmed that these crayfish were probably left by satiated otters. The most important prey item in a majority of otter scat analysis studies is fish, followed closely by crayfish. Otters will take advantage of other prey, such as frogs, salamanders, ducks, muskrats, an occasional young beaver, mice, snakes, insects and even turtles when readily obtainable, but fish and crayfish are first and second choices.


Fisher Hunting Strategy

2-20-13 fisher hunting technique IMG_2988I have never heard of this particular fisher hunting technique, nor have I seen or read about it before, but there’s no denying that a fisher made these marks in the snow and that they tell the story of how it captured a mouse or vole. It’s likely that the fisher could hear or smell that the rodent tunnel in the subnivean layer was occupied. It looks as though the fisher methodically scraped snow towards the center of the circle, going completely around the tree in an attempt to trap and/or expose the mouse or vole within the circle. It succeeded in opening up the rodent tunnel (the hole is in the dead center of the photograph), and if the tiny droplets of blood on the snow near the hole are any indication, was successful in capturing its prey.


North American River Otters

2-11-13 river otters otters2 IMG_1386River otters are the most aquatic members of the weasel family. They eat the whole gamut of aquatic prey, including fish, frogs, crayfish, salamanders and turtles – not to mention snakes, small birds, mammals, earthworms and insects. It would not be an exaggeration to say that this threesome consumed a minimum of 15 fish and crayfish within half an hour. Look for signs of their sliding in the snow, both down slopes as well as on level ground.


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