An online resource based on the award-winning nature guide

Beavers

Beavers To The Rescue

12-23-15 beaver dam & pussy willow IMG_5739With peepers peeping and pussy willows starting to poke their heads out of local willows in mid- late December, it is clear that in the coming years humans will need to adapt to the effects of climate change. Help with that mission may come from many sources, including beavers, whose landscape alterations have been shown to mitigate many of the more extreme conditions caused by climate change. Where beaver dams are persistent, they may sequester sediment and create wet meadows that can moderate floods, augment early summer baseflows, sequester carbon in soils and standing biomass, decrease ecological problems posed by earlier spring stream recession, and potentially help cool early summer and post-wildfire stream temperatures. (Jeff Baldwin, California Fish & Game) How fortunate that silk hats became fashionable in the early 1800’s, decreasing the demand for beaver pelts and rescuing beavers from extinction.


Rodent Incisors

12-3 woodchuck skull IMG_7187Rodents have two pairs of incisors that oppose each other; two in the front of the upper jaw and two in the front of the lower jaw. These four teeth never stop growing, and thus have to be constantly filed down. (Squirrel incisors grow about one-half inch a month.) While nipping herbaceous plants and cutting into bark help do this, it isn’t enough to significantly wear down the teeth. When mice, beavers, woodchucks and other rodents nip or gnaw food, they move their jaws in such a way that these two pairs of teeth grind against each other. Most rodents have hard orange enamel on the outer side of their incisors (woodchucks are our only rodent with white enamel), and softer dentine in the back. When the incisors grind against each other, the dentine wears away faster than the enamel, creating a sharp, chisel-shaped edge to the incisors. This, more than anything else, keeps the growth of rodent incisors under control, just as a nail file keeps our nails from getting too long.

If a rodent breaks an incisor, there is nothing to wear down the opposing incisor. The tooth opposite the missing incisor will continue to grow unchecked in a circle until it causes the death of the rodent, either by piercing its skull or by preventing the animal from being able to eat. In the pictured woodchuck skull, the lower left incisor has broken off, allowing the upper left incisor to grow through the woodchuck’s palate and into its brain.

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.


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.

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


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)

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.


Beavers See Daylight

4-17-15 beaver 281Imagine sharing dark, damp, cramped living quarters under pond ice with at least three other individuals for four to five months. Then imagine an increasing amount of light filtering through ice that is getting thinner and thinner. Finally the day comes when you are able to break through the ice and crawl out of the water onto land. The sudden brightness and heat provided by the sun, the availability of fresh vegetation to eat and the opportunity to thoroughly groom oneself in the open air must make an unimaginable sensory impact on a beaver in early spring.

Naturally Curious blog will have a brief hiatus until next Thursday, 4/23, so that a Naturally Curious Day by Day (my next adult book) chapter deadline can be met.

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. Thank you.


Beavers Mating

2-24-15 beaver3 IMG_3415Reproductive activity begins when a beaver reaches the age of three years. Beavers mate in January and February, with the peak activity in mid-February. Typically mating takes place in the water (under the ice), but can occur inside their lodge. Kits, usually three or four, will be born in May or June. Beavers are monogamous and pair for life. (Note: ponds still frozen – photo not recent)

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.


How Beavers Digest Cellulose

12-26-14 beaver sign 125Some beavers are still managing to find openings in their ponds which give them access to fresh cambium, the soft layer of wood just under the bark of a tree. Cambium contains a lot of cellulose, in addition to starches and sugars. Like all herbivores, beavers do not possess enzymes that are capable of breaking down the large cellulose molecules (cellulases). In their place, beavers employ micro-organisms, such as bacteria, that can break down cellulose.

These bacteria are located in a pouch called a cecum, located at the beginning of the large intestine. (Ruminants such as moose and deer have rumens in place of ceca.) Colonies of these microorganisms in a beaver’s intestines digest up to 30% of the cellulose from the woody material that it eats. Further nutrients are recovered in the form of fecal pellets that the beaver re-ingests.

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.


Follow

Get every new post delivered to your Inbox.

Join 3,965 other followers