Dave Hallock, Eldora. Beavers are the engineers of the animal world. They build dams, lodges and canals to regulate water levels that provide shelter and access to food. Their dams raise the water table and increase the size of wetlands, benefiting the many animal species that depend on them, such as waterfowl and neotropical migratory birds that nest in willows (Wilson’s warblers, yellow warblers and dusky flycatchers to name a few). Beaver lodges, constructed with sticks, rocks, mud and similar objects, may be totally surrounded by water or built partially on land. They typically have an underwater entrance 3 feet or less below the water surface, which leads into a feeding chamber and an elevated sleeping chamber. Winter temperatures in the lodge have been found to be relatively stable. The largest lodge ever recorded was over 6 feet high above the water and over 36 feet in diameter, about the size of a typical Eldora cabin.

Much of the exploration of the American West in the early 1800s was directly related to the exploitation of beaver, whose pelts were used to make gentlemen’s hats.  The St. Vrain Creek in northern Boulder County is named after Ceran St. Vrain, who partnered with the Bent Brothers (of Bent’s Fort fame in southeast Colorado) in the fur trading business.  In 1837 they established Fort St. Vrain, located at the confluence of St. Vrain Creek and the South Platte River in Weld County. Beavers were likely saved from extinction in the mid-nineteenth century as Chinese silk became the preferred material for hats.

Beavers generally live in extended family colonies, consisting of adults, yearlings and juveniles, with young animals dispersing from the colony around the age of two. They are most active at night, dawn and dusk. While foraging, they usually do not range much more than several hundred yards from water. They develop underwater food caches in areas like ours where the water surface freezes during the winter. 

Being semiaquatic, beavers are restricted to stream ecosystems for habitat, favoring areas with abundant willows, aspen and/or cottonwoods. Their favorite locations to establish lodges in the mountains of Boulder County are glaciated valleys like Caribou Ranch, Arapaho Ranch and Woodland Flats. In these wide, relatively flat valleys, stream flows are gentler than in steep canyons. The waters are easier for beavers to manipulate with dams. Dams and lodges can be constructed off of the main stem of the creek, requiring less maintenance after spring runoff. 

Beavers can have profound effects on the stretches of stream they inhabit, as well as areas downstream. By raising the water table, they expand the size of wetlands. Beaver enhanced wetlands, with their mosaic of willow and birch shrublands, ponds and emergent vegetation, are some of the richest breeding bird habitats in Colorado. They are nodes of high biodiversity. Beaver dam complexes help catch and retain flood waters and sediment. In essence, they help manage watersheds. They help retain more water on our local landscape. During these times of global warming, that is a significant benefit to having them around.

But because they live along streams there can be conflicts with humans as we also like to be near water. Much of our infrastructure (roads, ditches, dwellings) is found along streams and they like to cut aspen on our properties.

Think of beaver as a legal way to keep more water on our landscape. And for this one factor alone, besides all the other benefits, try to see them more as helping to maintain a healthy ecosystem and less as a nuisance.

Following are some of the September nature happenings in the Nederland area. I call this the time of “dropping cones and shedding needles.” Squirrels are dropping pinecones to the ground for winter reserves to be stashed in their middens. Needles on many conifers will start turning brown, particularly on lower branches and the inner portions of other branches, as the trees shed excess foliage. Of course, if you see all the needles turning brown, you may have a larger problem.  

Berries continue to ripen. Look for huckleberries, chokecherries, raspberries and others. If you hit a good patch of huckleberries, you can smell their wonderful aroma in the air. Black bear diets heavily shift toward berries as they gorge themselves for winter hibernation; this is evident in their scat.

Bull elk are bugling. The peak of the rut occurs around the end of September. Moose also start having other things on their mind, as breeding begins around mid-September and runs until early November.

Pocket gophers will continue to aerate the ground by tunneling and leaving mounds of dirt on the surface.

Birds are on the move. Flocks of sparrows, warblers and bluebirds are coming from the north, while local birds are flocking up and getting ready to head south. The tundra is a good place to see migrating birds that are feeding on abundant grasshopper and cricket populations. Raptors, including red-tailed hawks, golden eagles, northern harriers, American kestrels, peregrine falcons and prairie falcons, frequent the tundra during fall migration.

A few butterflies will still be around in September. Some of these, like commas (orange with black spots and angular wings) and mourning cloaks (large, dark brown with yellow stripes), will overwinter as adults and can emerge during warm periods in winter or in early spring. While not much is known about painted ladies migrating south, some are often seen in September and October in high elevation meadows making a strong southwest movement. (Some of the information about beaver in this article was gleaned from Mammals of Colorado by Armstrong, Fitzgerald, and Meaney) .

(Originally published in the September 5, 2019, print edition of The Mountain-Ear.)