Birds of Jefferson County: Accipiters

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“What is that hawk who comes into my yard and eats ‘my’ birds?”

These hawks are probably Accipiters, a sub-group of the birds of prey most easily distinguished by their long tails and short, broad, rounded wings which allow them to maneuver in and out of trees. Their normal hunting ground is in the forest, but Accipiters have been loosing out to houses, commercial developments and highways. The many small birds that consititute their prey base have adapted to urban living and bird feeders, so seeing these Accipiters hunting in your back yard and nesting in urban settings is becoming more and more commonplace.

The two Accipiters most often seen in the Denver area are the Cooper’s Hawk (Accipiter cooperii) and the Sharp-shinned hawk (Accipiter striatus) – the Sharpy. If you’re in your yard and suddenly you notice that all the birds are fleeing from the feeders, and then everything suddenly gets quiet, search the trees close by. You may see a Cooper’s Hawk or Sharpy quietly sitting and waiting for some small bird to fly into harm’s way.

In my yard I have seen an Evening Grosbeak, which measures just over 7 inches tip to tail, taken by an Accipitor. I have also watched as a Cooper’s Hawk stepped into my 2″ deep birdbath and spent 15 minutes deciding whether or not to take a bath. Then he splashed about for another 30 minutes, spreading his wings and bending over sideways to bathe. The Cooper’s Hawk is about 17″ long. The Sharpy is smaller, about 12″ long, however – because the female Sharpy is larger than the male, a Sharp-shinned female can be about the same size as a male Cooper’s Hawk.

Photo - AccipitersTelling the two species apart can be difficult, the accompanying photo is representative of either species, although, by consensus of opinion, we think the Accipiter is a Cooper’s Hawk and his prey a sparrow of some sort. As adults, both are dark gray above and lighter below with buff-colored stripes on the breast. The most distinguishing feature of both species is the tail…long, wide and banded, alternating dark and light brown, with white tipping at the end. A Sharpy has a straight-edged tail with a little white at the outer end. The Cooper’s Hawk has a rounded tail with more white showing at the end. Feather wear can modify the appearance of the tail feathers, causing identification confusion. Adult birds of both species have red eyes while their youngsters have yellow eyes. Sharpys often have some white blotchy feathers on the back.

In flight, the Sharpy tucks its head into its wings, while the Cooper’s Hawk extends its head – some have described a Cooper’s Hawk in flight as “a flying cross.” A Cooper’s Hawk weighs about a pound while a Sharpy weighs only about half a pound.

One day I was at my bird feeders when one came at me chasing a sparrow – couldn’t tell if it was a Cooper’s Hawk or a Sharpy, they were moving so fast. The sparrow went to my right and the Accipiter to my left. The sparrow got away. In the bird world there are predators and there are prey…don’t be too alarmed if you witness an Accipiter doing what he’s supposed to be doing at your feeder or in your yard. This is just part of the way of the wild.

Copyright © 2011 Ann Bonnell

Big Bluestem: Plant of the Future

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This fall I had an email from a botanist friend: “What’s going on with big bluestem?” After he pointed it out, I noticed that, sure enough, this species, one of the dominant grasses in the tallgrass prairie (as in the source of the original Kansas sods that once housed the homesteaders), is bustin’ out all over the foothills! Big bluestem typically occurs on the slopes of our mountain front, but has been expanding in recent years. In 2010, this warm-season grass had an extraordinary year. Its abundance first drew attention at Lookout Mountain, on the slopes of Windy Saddle Park and adjacent areas, where you can probably still spot patches of its russet fall color when the ground is free of snow, even if you’re driving by on 6th Avenue. If you’re on the Lariat Trail, big bluestem borders the south side of the road east of Windy Saddle. This time of year, when it might seem there’s little to interest plant lovers, big bluestem and its cousins in the grass family provide color in the landscape.

Tallgrass prairie, whether here or in the East, is a tattered remnant of what it was in its glory days. We’re lucky to have sizable patches in Jeffco; efforts to protect some have been underway for more than 20 years. It’s been years since we talked tallgrass prairie here in the PJ newsletter, but the Board has continued to monitor and comment on developments in the Rocky Flats area, where our best examples of this rare ecosystem survive, including the Ranson/Edwards and Jewell Mountain properties. Boulder conveniently protected several hundred acres of the latter. Patches of big bluestem on the foothills slopes are fine, but limited, reminders of the more extensive remnant prairie that once rolled out across the county but has retreated to a fringe along the mountain front. Most of what you see just northwest of Highways 93 and 72 is also tallgrass prairie.

Big Bluestem in Jeffco’s Landscape

Look for these foothills patches primarily on unforested south- and east-facing slopes: on most central slopes visible west of Highway 93, and on the north sides of our canyons, from Bear Creek to Golden Gate. In Mt. Galbraith Park, you can see the colorful auburn patches across the canyon as you make your way up the trail. Driving west on I-70, look for it to the north as you enter the foothills, on the slopes in Matthews-Winters Park. In the southwest part of Red Rocks Park, it occurs on level sites, more prairielike, because that area has been protected and contains isolated spots where the Rocky Flats alluvium has managed to persist on lands that would otherwise have been cultivated or developed. In fall, big bluestem blends perfectly with the outcrops of the Fountain Formation.

Lack of development and a somewhat inhospitable climate have also protected the Rocky Flats area. The extremely cobbly soils, beloved of gravel companies, hampered agricultural attempts on much of the area and enhanced the available moisture content for the growth of these taller species. Because the area is unplowed, in part, these soils are considered among the oldest in Colorado, with some estimates placing their age at 2 million years. But big bluestem’s expression/visibility in the landscape of any given year reflects how we’re doing on overall precipitation and temperature.

The Water Year and Other Influences

Based on the 30-yr average precipitation, our wettest month of the year should be May. When it is, that’s about perfect for big bluestem and other warm-season grasses (including blue grama, sideoats grama, little bluestem, and switchgrass), which are just getting started as the weather warms toward summer. By June, the cool-season grasses (such as the common lawn grasses, including Kentucky bluegrass, which take advantage of early season moisture to start growth) will be ready to flower and set seed, but you’ll still have to hunt around on the ground to find evidence that big bluestem is even alive. Large clumps of hairy, velvety blue-green leaves will be your hint.

In July, those spreading clumps send up tall flowering shoots, which produce the “turkey-foot” seed heads by August. When cool-season grasses are giving it up and their seed has scattered, big bluestem ripens into the terra cotta masses that reveal its presence even from a distance.

This seasonal habit represents an entirely different metabolism (called “C4”) in these plants, which use carbon along different pathways than many familiar plants. According to some researchers, this may give them an advantage under conditions of elevated carbon dioxide (think global climate change), especially during drought. Like many grasses, big bluestem is also adapted to grazing and fire, but not if they occur too frequently.

Interestingly, although it seemed, until recent snows, that it’s been droughty for several months, 2010 was an above average moisture year during its first half, giving big bluestem the start it needed. In fact, rainfall in this part of the county has been at or above normal every month from April 2009 through last June. (Later records have not yet been posted online.) Average temperatures have also hovered a degree or two above normal for several years (except 2008); most of the past decade has been warm. Temperature and moisture conditions have apparently encouraged big bluestem, a species that prefers a little more moisture and warmth than is the rule in Colorado. If we get too dry and warm, we’re apt to see more of its cousin, little bluestem, but as long as it finds a moist spot, big bluestem will remain a part of the county’s natural prospect. If you haven’t seen it, this winter is a great time to go looking for it.

To see temp/precip data go to: http://ccc.atmos.colostate.edu/coloradowater.php

Big Bluestem (grass),
Andropogon gerardii

  • Warm-season sod-forming grass.
  • Height: 4-5 feet in Colorado, occasionally taller; to 8 ft in prairie states.
  • Occurs in all but the five westernmost of the lower 48 states, as well as the central provinces of Canada. Most abundant in eastern Great Plains.
  • Dominant and characteristic grass of the tallgrass prairie ecosystem.
  • Flowering heads are 4-5 inches long, with 3 (or more) spreading branches, suggesting its other common name: turkeyfoot

Copyright © 2011 Sally L. White