An online resource based on the award-winning nature guide

Herbivores

Porcupine Tracks

2-5-16 w's porcupine IMG_3938Alas, yesterday’s Mystery Photo ‘twas not made by a squirrel loaded down with a bag of nuts, a guess hazarded by one reader, but, as most of you knew, it was created by a Porcupine, or Quill Pig (Erethizon dorsatum). A bit pigeon-toed, Porcupines walk with their feet pointed slightly inward, with their feet flat on the ground. Their pebbly soles rarely leave a distinctive pattern, and their toe pads are not usually evident, but under the right conditions, their nails do make an impression. Usually a Porcupine’s quill-laden tail is raised slightly as it moves, but occasionally it drags along the surface of the snow as the Porcupine walks, producing a broad band composed of very fine lines that weaves between the Porcupine’s tracks, as in yesterday’s photo.

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Moose Ruminating

12-10-14  moose chewing cud IMG_4970Moose are ruminants, as are cattle, goats, sheep and deer; they have a four-chambered stomach, which is necessary in order to digest the cellulose in the vegetation they consume. Food goes to the rumen and the reticulum, the first two chambers, which contain bacteria and other microorganisms that help digest the cellulose as it mixes with saliva. Here the food separates into solids and liquid material and the solids clump together to form the cud, which is regurgitated and chewed a second time in order to break it down into smaller bits. The third chamber, or omasum, functions as a pump, sending the food to the final chamber, the abomasum, where the digestion process is completed.

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Beaver Incisors

10-29-15 beaver incisor marks 025Yesterday’s design was made by a beaver as it removed bark from a tree. The light-colored, curved little “bumps” that run horizontally across the middle of the tree were made by the two incisors in the beaver’s upper jaw. When eating the sought-after cambium layer of a tree, beavers grip the tree with their two upper incisors as they scrape towards their upper jaw with their two bottom incisors, sometimes creating this pattern. (Individual marks where the upper incisors gripped the bark and the four incisors didn’t quite meet can be seen in the insert.)

The ever-growing incisors of rodents are harder on the front surface (outer layer is hard enamel, colored orange from iron in a beaver’s diet) than the back (softer dentine), so the back of each incisor wears away faster than the front, creating a sharp, chisel-like edge to these four specialized teeth. So functional are beavers incisors as cutting instruments, Native Americans used to insert a beaver incisor in a wooden handle and use it to cut bones and to shape their horn-tipped spears.

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Dung Beetle Feeding on Bear Scat

10-16 dung beetle 127Wherever there is scat, or dung, there are dung beetles. This is a photograph of a dung beetle in heaven as it has located a black bear’s gigantic (apple-filled) scat, which will provide it with food for a long, long time. Some species of dung beetles (rollers) shape pieces into balls and roll them away and bury them to eat later or lay their eggs on. Some species (tunnelers) bury their dung by tunneling underneath the pile of scat. And a third group (dwellers) actually lives inside dung piles.

Most dung beetles prefer the scat of herbivores. There are always bits of food that do not get digested, and these bits are what a dung beetle feeds on. Dung beetle larvae eat the solids, while adult beetles drink the liquids contained in the scat. A given species of dung beetle typically prefers the dung of a certain species or group of animals, and does not touch the dung of any other species.

Dung beetles have a brain that is the size of a grain of rice, yet they are very sophisticated insects. They use celestial clues (the Milky Way) in order to roll balls of dung in a straight line. Dung beetles are known for “dancing,” which helps them orient themselves after their path has been disrupted. They use their dung balls to regulate their temperature, and cool off. (In very warm climates, around noon, when the sun is at its peak, dung beetles will routinely climb atop their dung balls to give their feet a break from the hot ground. Thermal imaging has shown that dung balls are measurably cooler than the surrounding environment, probably because of their moisture content.) And dung beetles keep track of the number of steps they take and the direction from which they came (instead of landmarks) in order to return to their nest with a ball of dung.

Even though they are remarkably clever, dung beetles can be duped! A flowering plant native to South Africa (Ceratocaryum argenteum) produces large, round nuts that are strikingly similar in appearance, smell, and chemical composition to antelope droppings, which the dung beetles accordingly roll away and bury, effectively sowing a new generation of C. argenteum.

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Porcupines Foraging

10-1-15  porcupine in leaves IMG_2537There are a few weeks in September and October when acorns (and beechnuts) are mature enough to eat, but haven’t yet fallen to the ground. Porcupines take advantage of this nutritious supply of food that is not yet accessible to small rodents, deer and turkeys, and climb oak trees to consume acorns. Because an average porcupine weighs between 12 and 35 pounds, it is unable to climb all the way out to the end of a branch, where acorns are located, so it nips off the tips of fruit-bearing branches and then scoops out the acorn, leaving the cap still attached to the branch (diagnostic porcupine sign). When all the acorns on a branch have been eaten, the branch is discarded. You can often find many of these branch tips, or “nip twigs,” in the canopy of large oaks on a good mast year, but inevitably some fall to the ground. The end of the twig is usually cut at a 45° angle, and often you can see the lines made by the porcupine’s incisors. (Beechnuts are also harvested in this manner, as are the cones and terminal buds of eastern hemlock in winter.) Red squirrels also nip twigs in order to reach fruit, but typically do so when they harvest the cones and terminal buds of conifers. (Thanks to Ethel & Michael Weinberger for photo opportunity)

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Muskrats Busy Feeding

7-24-15  muskrats IMG_4435For the most part, muskrats are herbivores. They consume with relish the leaves, stems and rhizomes of emergent aquatic plants such as cattails, bulrushes, sedges, horsetails, water lilies and arrowheads. Fish, frogs and invertebrates, including crayfish and clams, are also eaten to a lesser extent. Muskrats are voracious eaters (captive muskrats eat 25 – 30% of their weight daily). When their numbers are very high, muskrats can cause what is referred to as an “eat-out,” where they mow down everything in sight.

Like beavers, muskrats can close their upper lips behind their incisors in order to cut plants underwater without taking in water and choking. (photo: two young muskrats feeding on aquatic vegetation)

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Rodents Recycling

3-13-15  gray squirrel 001Bones, antlers, skulls, turtle shells – all are recycled relatively quickly by rodents seeking a source of minerals, particularly calcium and phosphorus. All rodents possess four incisors, two in the front of the upper jaw and two opposite these, on the bottom jaw. These incisors, unlike other teeth, never stop growing. By gnawing on hard objects such as bones, rodents keep their incisors paired down. If an incisor is broken or lost, the opposing incisor will continue growing in a circle, having nothing to grind against, causing the rodent to die of starvation or from having its brain pierced (through the roof of the rodent’s mouth) by the ever-growing incisor. In this photograph, a gray squirrel is obtaining minerals and sharpening its incisors on a moose skull that a human wedged into the crotch of a tree.

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