Dave’s Nature Almanac: September
Nature Almanac: Monthly Menu
Prairie Fireworks!
Tallgrass prairie changes color in September! Big bluestem grass (pictured) can become all sorts of reds, wine-colors and even purple. Other grasses also change. You can see it well at Shanahan Ridge and along the South Boulder Creek trail near the Bobolink Trailhead.
Many trails provide a colorful show this month. Asters are the real show-stealers. White asters include the Heath Aster and Porter's Aster, which can be distinguished by their foliage. The former has pale-green fuzzy little leaves while the latter's leaves are dark green, long and thin and the plant is less dense. The taller Smooth Aster has purple or bluish flowers, each with a yellow center. Golden Asters sprawl close to the ground. Their flowers are a lovely yellow-orange color. Curly-cup Gumweed flowers look a lot like the Golden Asters, but the plant is tall and spindly. Each flower sits in a small cup with tiny sticky appendages. Touch one and smell the resin on your finger. Dotted Gayfeather is a low plant with needle-like leaves and gorgeous magenta floral spires. Several species of Goldenrod also occur on OSMP trails. They provide nectar for late summer butterflies. And keep your eyes peeled for gentians, which often mark the end of summer. Blue Gentians are only a few inches tall, but so intensely colored that they will reward your search.
Follow this link to the wildflower photo gallery to see more identified pictures of fall wildflowers, native grasses and shrubs.
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Antlers vs. Horns
Male deer grow antlers each fall, then shed them in late winter only to re grow them again in autumn. Antlers are bony appendages that grow from the skull. While they are growing, they are supplied with blood through a network of vessels and have a soft, fuzzy appearance (see the buck in the picture above). When the antlers are complete, the blood flow stops and their thin skin covering, called velvet, begins to come off in strips. Bucks hasten the process by rubbing and scraping their antlers against trees and bushes -- as any backyard gardener can attest! This is a good time to protect delicate saplings and ornamental shrubs with deer netting.
Other animals that grow antlers include elk and moose. Bighorn sheep and bison grow horns, which are permanent structures that are not shed and re-grown. Horns are often found on both males and females. They have a core of bone covered by a sheath of keratin - the same material as your fingernails.
Pronghorns, which belong to a unique group of hoofed animals, are the real oddballs: they grow horns with a bony core and keratin sheath, which they shed and regrow each year like antlers!
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At Home in the Milky Way
Under a dark sky in September, you can see the Milky Way stretching across the sky from north to south. That faint glowing band is our home galaxy - an incredibly vast city of stars swirling in a flat disk with a bulge at the center. The photo above shows another galaxy called M66 that is similar to the Milky Way in size and structure. But since we’re down inside the disk itself, we never see it like this. To us, it appears as a flat glowing band.
The Sun and our solar system are located about ⅓ of the way from the center, in a wispy stream of stars between the principle spiral arms. Our galaxy is thought to contain around 300 billion stars - enough for every person in the United States to have 1000 of their very own. Every star you can see with your naked eye lies within the Milky Way, and would fit under your pinky fingernail when pressed against the photo. The rest of the stars are so far away that you don’t seen them as individual points of light, but rather a diffuse glow.
If you follow the Milky across the sky, you can see overhead a dark band running through it that seems to split the star river into two streams. This is a huge dark cloud of gas, like the black swirls you can see in the photo. Toward the southern horizon, the glow spreads out and becomes wider as you face into the central bulge at the core of our galaxy. Deep space photographs show us that the universe contains thousands upon thousands of galaxies like ours, each one a vast star city.
Readabout the Milky Way’s neighboring galaxy, the huge spiral in Andromeda, in November’s almanac.
Wilson’s Warblers will show up in backyards and in shrubs along trails this month. They look like active yellow canaries (the male has an elegant black cap). Their journey takes them from far northern Canada and Alaska, where they nest on the ground in willow thickets, all the way to the jungles of Costa Rica. They are one of our only migrants that hangs out in the páramo - the treeless grass and bamboo forests of the high altitude tropics. Learn more about these and Boulder’s other tropical migrants on my spring “Jungle Birds” hike!
In September, some of last month’s Rufous Hummingbirds are still around on their annual migration south from breeding grounds in the Northwest. Smaller - and more aggressive - than our local Broad-tailed Hummers, these feisty little things will take over your feeder or flower bed and drive the Broad-tails away. They are a rusty reddish-brown, and males have a distinct coppery-colored throat gorget when the sunlight strikes them just right.
Like the Broad-tails, male Rufous Hummingbirds make a high-pitched trill as they fly, using specially modified vibrating tail feathers. I think they sound more metallic. The sound alerts other hummingbirds to their presence and also impresses females as the males perform their sexy death-defying mating dive.
Despite their tiny size, they have the longest migration route of any of our hummingbirds, some traveling from southern Alaska all the way into north and central Mexico. Since they travel such long distances through many habitats, Rufous Hummingbirds are especially sensitive to the effects of climate change. Parts of their range in Oregon and Washington may become unsuitable, driving breeding birds farther north into Canada.