Spotlight on Parks: Rocky Mountain Arsenal National Wildlife Refuge

A short drive from Denver lies a remarkably diverse wildlife habitat: Rocky Mountain Arsenal National Wildlife Refuge. The area, previously a chemical weapon and agricultural chemical manufacturing facility, was designated a national wildlife refuge in 1992 and reached its full size of almost 16,000 acres in 2010. The refuge is notable for being one of the largest urban wildlife refuges in the United States.

I visited the refuge a few weeks ago during National Wildlife Refuge Week. The first thing that stood out to me was definitely how close the refuge is to our state capital. The second was how secluded it felt for all of that. There weren’t very many people out and about so I could pretend I was the only one there.

The visitor center was closed for Columbus day, so I parked and literally took a hike. The refuge features a rather large black-tailed prairie dog town and the prairie dogs eyed me warily as I wandered down the path. My presence scared off a coyote that might have been looking for a less observant town resident for breakfast. It looked back at me briefly before melting into the grass and trees. I didn’t see any burrowing owls who also make use of prairie dog dens, but I did see a couple of cottontail rabbits hunkered down.

Mule deer buck at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.
Mule deer buck at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.

This time of year is a great time to see deer and I saw several, including a big buck lying by the wildlife drive with a huge complement of antlers. Both mule and white-tailed deer are present in Rocky Mountain Arsenal, though I only saw the former while I was there. I also saw a lot of birds, including a great-horned owl resting in a tree, several hawks and falcons (American kestrel and red-tailed and Cooper’s hawks), and a whole slew of waterfowl using the refuge’s ponds as a stopover for migration. The waterfowl I saw included several species of ducks (mallards, green-winged teal, and northern shovelers), a pied-billed grebe, and American coots.

One of the members of the bison herd at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.
One of the members of the bison herd at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.

What’s really special about the refuge is that it was chosen for a bison reintroduction project in 2007. Bison were introduced from Montana as an experiment to see if they could survive. They did and now they roam an area of 2,600 acres within the refuge. Currently, that area is fenced off with cattle guards to prevent them from moving to other areas of the refuge along the road, but the plan is to eventually open up 12,000 acres to the bison. I saw one bison on my visit. It seemed curious to see me as we eyed each other through the fence. I wonder what it thought of my being there?

Rocky Mountain Arsenal is open almost all year long from sunrise to sunset. It’s closed on Thanksgiving, Christmas, and New Year’s Day. The visitor center is open from 9:00am to 4:00pm Wednesday through Sunday and is closed on all Federal holidays. I encourage you to go visit. I’m sure it’s spectacular no matter what time of year, but autumn in particular is a good time to visit.

Turn, Turn, Turn

Autumn is in full swing now. Everywhere I look is a sea of nearly unbroken gold.  According to this map, it’s at or past peak autumn color in most of Colorado. There are so many leaves falling that they remind me of large, yellow snow flakes. But what makes them yellow? What makes the trees in New England orange or red or burgundy?

Fall color at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.
Fall color at Rocky Mountain Arsenal National Wildlife Refuge. Photo by Jamie Simo.

From bud break until just before it leaves the tree or shrub (not just trees change color), a deciduous leaf is green. Deciduous means “shedding at maturity.” For deciduous trees and shrubs, this means once a year during the fall. Did you know that your “baby teeth” are also known as deciduous teeth because they fall out after a certain point? Deciduous is the opposite of “evergreen,” which is the term used to refer to trees or shrubs that retain their leaves, like pines (what we call “needles” are just really flattened and elongated leaves).

A leaf is green in the spring and summer because of chlorophyll. Chlorophyll is a molecule that allows the plant to harness sunlight. In the presence of water and carbon dioxide, the sunlight captured by the chlorophyll can then be used to produce the sugar (glucose) that the plant needs to survive. Oxygen is actually only a waste product of this process, which is known as “photosynthesis.”

When days start getting shorter, this signals to the tree or shrub that it will soon be too dark and dry to keep photosynthesizing. So, similar to hibernating animals, deciduous trees and shrubs also prepare to save energy during the winter by going into a kind of dormancy where they live off of stored glucose. During this time the chlorophyll in the plant’s leaves begins to break down and other pigments in the leaf become visible. These pigments, called “carotenoids,” are responsible for the bright yellows and oranges you see in trees like aspens or cottonwoods. Carotenoids are also responsible for the color of vegetables like carrots.

When I lived on the east coast, there were many trees, particularly maples, that turned amazing shades of crimson some years. The red color of these and other trees is due to a different pigment called anthocyanin. Anthocyanins are what make blueberries blue or cherries red.

New England fall colors. Photo by Chris Bastian44 on Flickr. http://weather.thefuntimesguide.com/2010/09/new_england_fall_colors.php
New England fall colors. Photo by Chris Bastian44 on Flickr. http://weather.thefuntimesguide.com/2010/09/new_england_fall_colors.php

Unlike carotenoids, anthocyanins are not present in the leaf year round. According to a fairly recent study, anthocyanins are produced exclusively in the fall as a way to protect the plant from excessive light exposure, which may cause damage to leaves that, in turn, could make it more difficult for the plant to recover nutrients. Evidence to support this is that leaves in more shaded areas do not produce anthocyanins. Whatever the reason for their production, anthocyanins produce the most vivid colors in years where the autumn has been sunny and somewhat dry with cool, but not freezing nighttime temperatures.

Do you like to travel to watch the leaves turn?

Fall for the Snake

Fall is fully upon us here in Colorado, though it’s been pretty warm the last few days. When you think of fall and animal behavior, the first thing you might think of is birds migrating or certain mammals hibernating, but a couple of recent encounters have put snakes on my radar in a big way.

A pair of mating common garter snakes at Sawhill Ponds in Boulder, CO. Photo by Jamie Simo.
A pair of mating common garter snakes at Sawhill Ponds in Boulder, CO. Photo by Jamie Simo.

A few weeks ago I saw a pair of common garter snakes cavorting in the grass at Sawhill Ponds in Boulder. The common or red-sided garter snake (Thamnophis sirtalis) is a really interesting species. Unlike a lot of snakes, garter snakes bear live young instead of laying eggs, so the female is noticeably larger than the male in order to accommodate babies. The snakes I saw were almost certainly a male and female pair engaged in breeding because one was definitely smaller and they had their tails entwined. While spring is a common time for snakes to mate, according to the Idaho Museum of Natural History, common garter snakes may also breed in the fall.

This past Saturday I had another snake encounter. Coincidentally, it was with another snake that bears live young. I literally almost ran into my very first prairie rattlesnake (Crotalus viridis) in the wild at Chatfield State Park in Littleton. It was stretched out partially on the trail, perhaps sunbathing. It was certainly a beautiful day for it. Whatever it was doing, it definitely wasn’t happy to be disturbed, rattling and coiling up for a strike if I got too close. Needless to say, I kept my distance!

Prairie rattlesnake coiled to strike at Chatfield State Park. Photo by Jamie Simo.
Prairie rattlesnake coiled to strike at Chatfield State Park. Photo by Jamie Simo.

Both days I saw the snakes were really warm. So what do snakes like those garter snakes or that rattlesnake do when the weather turns cold? Snakes are reptiles and so they rely on soaking up heat from their surroundings in order to warm up enough to move or undergo other bodily functions like digesting food. This means they’re “cold-blooded,” or “ectothermic,” as opposed to “warm-blooded” or “endothermic” like humans and other mammals whose body temperatures and functions are related to internal metabolic processes. Therefore, snakes “hibernate” during the winter.

The scientific term for reptile hibernation is “brumation.” During brumation, the reptile’s bodily functions grind nearly to a halt, though they’re not technically sleeping like mammals undergoing hibernation. For instance, they still need to keep hydrated. Snakes and other reptiles will look for an insulated place away from potential intrusion called a “hibernaculum” (plural hibernacula) to spend the season. A hibernaculum may be a den, a pile of leaves, a crawl space under your house, under water, or anywhere else where temperatures are relatively stable. Sometimes, a bunch of snakes will enter the same hibernaculum and overwinter there together curled up into a ball.

Brumation only occurs in areas with distinct warm and cold seasons, however. In tropical areas, though there may be some physical changes over the year, reptiles don’t typically brumate because temperatures are pretty steadily warm. There’s no need for dormancy. In artificial environments like with pet reptiles, unless brumation is induced, there’s no need for the animal to undergo it either. But that’s an entirely different topic.