Saturday, April 07, 2012

Why I Live Here: Moose in the Backyard

Usually we know that there have been moose in our yard by footprints or deeper tracks in the snow.  Or a pile of nuggets. 

Actually seeing them there is less frequent.  It always surprises me how animals this big can so easily blend into the background. 

The one out in the open snow is pretty easy to see, and it's what I saw when I looked out the kitchen window this morning, but the second one* in the trees took a bit longer to spot.

These two moose were stripping the bark from our willow trees and trimming our high bush cranberries.  You can see in the video the bare trunk under the freshly stripped bark.

There's a reason moose choose willow.  This is from a report
Willows of Interior Alaska by Dominique M. Collet, who is the author of the Alaska Insect book.
Salicin, the chemical that preceded acetylsalicylic acid (aspirin), was first isolated from willow. The bark of some willow species is rich in tannin used for the processing of leather. The primary use of willows today, however, is for reclamation of disturbed sites and stabilization of riverbanks.
In Great Britain and Scandinavia, where fossil fuels are expensive, there is a developing interest in willows as a source of renewable energy; the fast growing shoots are coppiced (harvested) every few years, and the dried chips are sent to electric power plants. This fuel burns clean, leaves little ash, and emits carbon less than or equal to that absorbed from the atmosphere by the willow during growth.

The foliage of most willow contain salicilin, a chemical (phenolic glycoside) that deters browsing by most generalist herbivorous insects and mammals. Only a small fraction of the diet of these herbivores, such as the snowshoe hare (Lepus americanus) can consist of willows because the salicin distresses the digestive tract just as aspirin (methyl salicylate) does when taken on an empty stomach. A few generalist herbivores, like the moth Orgia antiqua, are able to complete their development on willow alone.
Specialized herbivores, like moose (Alces alces) and to a lesser degree caribou (Rangifer tarandus), cope well with these chemicals in their browse and are able to tap this otherwise little used resource. For a few specialist herbivorous insects such as sawflies (Tenthredinidae) and leaf beetles (Chrysomelidae), the volatile phenolic glycoside even serves as feeding and oviposition cues.
Herbivores that do not feed on willow may still depend on the plants for shelter or for the microhabitat they create. This results in a compartmentalization of the fauna in willow-rich habitats: a majority of herbivorous species avoids feeding on willows while a small fraction is totally dependent on them.

*It's to the left of the greenhouse and and the two trees there.

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