Category: In the Field

Lizardtail (Saururus cernuus) is emerging from the wet streamsides.

Activity along the north side of the main pond continues briskly, with all four boxes occupied. Box #6 is still a-building, with eight Wood Duck eggs not yet under incubation.

At the downstream end of Barnyard Run, beyond the beaver dam near the observation tower (at right in this image), box #61 has hatched out 17 of 18 Hooded Merganser eggs. Several more boxes are due to hatch late this month.

A few weeks ago I posted about crayfish chimneys, but that post lacked an image. Here’s one to rectify the situation.

Two species of vireos (Vireo griseus and V. olivaceus) were heard but not seen. At least one Green Heron (Butorides virescens) was spotted over the wetland, as well as (suprisingly exposed in the open) a Pileated Woodpecker (Dryocopus pileatus). A birder at the tower pointed out an American Bittern (Botaurus lentiginosus) to me. Chickadees have taken over one of Melina’s boxes intended for Prothonotary Warblers. Virgina Rails (Rallus limicola) were reported in the past week, but we didn’t detect them today.

The forest floor is lightly frosted with drifts of Spring Beauty. Melina found a Hermit Thrush (Catharus guttatus) foraging at the edge of the parking lot; the first Common Yellowthroat (Geothlypis trichas) made his appearance.

Ten boxes have active nests, plus one with one cold Wood Duck egg that appears to be a false start. Box #68 is due to hatch out this week.

When I was out with Dirk last week, we looked at crayfish chimneys. We’re always glad to see evidence of crayfish (our most common is Cambarus diogenes) in the wetland, because they are an indicator species: they can’t tolerate certain water contaminants. In turn, as detritivores, they recycle decaying organic matter into the food web. And the question came up: what’s with the chimneys? what purpose do they serve? Turns out that authorities are not quite sure. It may be simply that the crayfish needs to do something with the mud it has excavated as it burrows down to the water table, so it leaves it at the entrance.

Spring Beauty (Claytonia virginica) is just starting to break through the leaf litter on the forest floor. Maples are heavy with blooms. The team spotted Rusty Blackbird (Euphagus carolinus) and Red-headed Woodpecker (Melanerpes erythrocephalus) along lower Barnyard Run. Box #67 has become a dump nest, with 26 eggs by last count. New bird arrivals on the scene: Tree Swallow (Tachycineta bicolor) and Purple Martin (Progne subis) winging after insects over the pond; ants-at-a-picnic Brown-headed Cowbird (Molothrus ater) deeper in the woods than usual; and Brown Thrasher (Toxostoma rufum) at the observation tower.

Adapted from my report to park staff and the nest box team:

A fast start to the season!

As of our third trip out, we have nesting activity in six boxes: #7, #13 (main pond), #77, #67, #61, and #68 (lower Barnyard Run). Three boxes are Hooded Merganser, two are Wood Duck, and one has 5 HM eggs and 2 WD eggs.

Alan and I cleaned out the squirrel drey from box #9 (and woke up a cranky squirrel, who promptly exited). We’ve been pulling trash from the run flowing into the main pond, but I think there is more to be found on the west bank. On the 14th, we spotted a Wood Duck pair standing on the boardwalk just beyond the observation tower.

Also on the 14th, Red-Winged Blackbird (Agelaius phoeniceus) and Eastern Phoebe (Sayornis phoebe) made their first appearance. On the 21st, we watched an Osprey (Pandion haliaetus) fishing over the main pond.

This past weekend threatened to burn me out on field work. A trip was rescheduled for Saturday, postponed by previous snows, and I put in some extra time towards my term project, also deferred due to weather.

Our final field trip for winter tree ID visited Glen Carlyn and Bluemont Parks along Four Mile Run (someone should put together a course on nothing but the natural history of the Four Mile Run watershed) and Theodore Roosevelt Island. Bluemont offers the county champion Chestnut Oak (Quercus montana); the slopes leading down from Harrison Street into Glen Carlyn feature Mountain Laurel (Kalmia latifolia); and Roosevelt Island has Baldcypress (Taxodium distichum) on the marshy District side along with some magnificent American Elms (Ulmus americana) on the Virginia side. We took a lunch break at Teddy’s memorial. Elizabeth pointed out a trick for finding Black Tupelo (Nyssa sylvatica): many of the trunks of mature trees have a sway about ten feet up, as if the tree is standing hip-cocked.

I picked up Leta and we hustled up to Little Bennett Regional Park in Clarksburg for a crepuscular show of American Woodcocks (Scolopax minor), on an outing led by Stephanie Mason. Beeent.

Sunday morning opened the work season at Huntley Meadows Park. Dave Lawlor and crew had already mounted three new boxes, including #80 here, so our job of filling and freshening with wood chips went fairly quickly. Melina and Larry found a Hooded Merganser nest already started; Alan and I evicted a squirrel from underused box #9.

We rarely see a pristine box, so I took snaps before and after the bedding went in.

Finally, an easy drive to Sky Meadows State Park to make some more IDs for my project. Mug shots of my two uncertain calls here: Sugar Maple (Acer saccharum) on the left and Gray Birch (Betula populifolia) on the right.

Over the weekend I did some field work at Huntley Meadows for my tree ID class, and I previewed conditions for the upcoming nest box season. There are still substantial patches of slush on the trails and boardwalk, and lots of downed tree limbs. The fast-growing trees suffered the most damage from winter storms. Lots of chunks of Red Maples and Viriginia Pines were on the ground; I clipped twigs from snapped boughs of Sassafras albidum (thanks, Elizabeth!) and Black Gum (Nyssa sylvatica). The most spectacular wreck was the top half of an Eastern Redcedar that you see, permanently separated from its bottom half.

With much schedule shuffling as a result of the recent snow disruption, we finally got out for our second field trip for winter tree ID, to a couple of spots along Four Mile Run. Proving that you don’t need a pristine natural area to learn about the world, Elizabeth started us at the dog park at Shirlington Park, a long strip of ground along the north side of the stream pinched in by the light industrial area located just to the north.

We looked at natives and invasives: we keyed out an American Basswood (Tilia americana) still showing some shreds of the bracts and stalks of its fruits; we worked with a large River Birch (Betula nigra) with its scaly bark; and we found beyond the west end of the park a massive Eastern Cottonwood (Populus deltoides).

Among other trees, Elizabeth used a Black Cherry (Prunus serotina) with its “burnt cornflakes” bark for a field quiz. Her field quizzes are very effective teaching tools. We’re asked to identify a tree, by key or whatever means, to species by common and scientific name—but most importantly, we’re asked to mark three observed characteristics that led to the identification. So we’re led to a structured way of collecting information about a tree that may not yield its secrets readily. And if one of the trees is an easy ID, like an ailanthus with its brutishly heavy twigs, the rule of three keeps us looking. It might be that I go to the field guide with a known tree and then look back at it to find a bud or scar feature.

We moved on a little upstream to a smallish habitat that supports a magnolia association: American Fringetree (Chionanthus virginicus), Poison Sumac (Toxicodendron vernix), and Sweetbay ( Magnolia virginiana), with Mountain Laurel (Kalmia latifolia) in an oak-heath community just up the slopes. The smooth-barked multistemmed Sweetbay in these parts retains a handful of green leaves over the winter. Farther northwest, at about mile marker 4.5 on the Four Mile Run Trail, Elizabeth showed us the Arlington County champion Green Ash (Fraxinus pennsylvanica).

First, the large riverside tree that was described as American Linden is now identified by Elizabeth as Eastern Cottonwood (Populus deltoides). Second, classmate Patty has posted a set of images from the trip.

The weather was once again kind to us, this time for our first field trip in winter woody plant ID (trees mostly, and some shrubs). We worked a short bit of the towpath of the (still iced-over) C&O Canal and the B section of the Billy Goat Trail in the Carderock Recreation Area, on the Maryland side of the Potomac just outside of the Beltway. Elizabeth Rives is teaching the class, and she’s started us out with the opposite-branching trees. So we spent time with various maples, ashes, and Flowering Dogwood (Cornus florida) today. I found that ID’ing one particular dogwood that wasn’t showing many buds to be a particular stumbling block.

We also looked at a Bitternut Hickory (Carya cardiformis) example, with its strongly yellow buds; the many-synonymed Musclewood (Carpinus caroliniana); Eastern Hophornbeam (Ostrya virginiana), a shaggy-barked catkin-bearing member of the birch family; Hackberry (Celitis occidentalis) with a corky bark that isn’t spongy like an elm. One more opposite-branching shrub was Black Haw Virburnum (Vibirnum prunifolia). Black Walnut (Juglans nigra) is allelopathic, but colonies of PawPaw (Asimina triloba) can tolerate it as a neighbor; the walnuts we saw didn’t look very purplish in the bark to me. The easy-fun tree for everyone was the shrubby Bladdernut (Staphylea trifolia), with its seeds rattling around in capsules that look like a fat man’s pants.

We previewed the oaks, on which we will spend a lot more time later. Bonus tree for the trip was a huge American Linden (Tilia americana). Bonus birds for the trip were a couple of Bald Eagles making their way down the river, seen fairly easily from our lunch break spot up on the rocks.

Taking a couple of classes, plus a concerted effort to spend more time in the field and documenting it, means I have lots of field trip notes this year.

• Wolf Rock, Chimney Rock, Catoctin Mountain Park, Maryland
• Blue Ridge, Ridge and Valley Provinces, Maryland
• Piedmont and Coastal Plain Provinces, Virginia
• Hawksbill Mountain, Shenandoah NP, Virginia
• Seneca Creek Greenway (partial), Maryland
• Soldiers Delight Natural Environment Area, Maryland
• Maryland wetlands
• Prince William Forest Park, Virginia
• Fairfax Cross County Trail, Virginia, Occoquan, Lorton, and Pohick Creek sections
• Fort C.F. Smith Park, Arlington, Virginia
• Potomac Heritage Trail (partial), Virginia
• Huntley Meadows Park, Fairfax County, Virginia

2008’s list.

I turned in my research report on Catoctin Mountain Park for my geology class last week. Unfortunately, I chose an area to write about that doesn’t have a full geologic map at the 15-minute level in print, so my coverage of the geologic structures is a little thin. And I really didn’t have time to get out to a library to check what resources were available. But I like the snapshots that I was able to incorporate into the report.

Turkey Vultures were kettling above the toll road to Leesburg as I set out for Catoctin Mountain Park in Frederick County, Maryland on this unnaturally warm and sunny November day. Some hiking, some field work in support of the paper that I am writing about the park for my geology class.

From the visitors’ center, I followed the clockwise loop suggested by PATC trail guides. The trails in the park are not blazed, but are wide and generally easy to follow, even when covered with the hazard of the season, slippery leaf litter. The side trip to Cunningham Falls is perhaps not worth the bother: the way to the falls is popular and boardwalked.

Back on the main circuit, I climbed to the Blue Ridge Summit Overlook (600′ from my starting point), snapping images of the Catoctin metabasalt. Crossing back to the east, I entered the region of the Weverton quartzite, exposed as Wolf Rock (at left) and Chimney Rock. I found a nice small boulder of Weverton conglomerate, too. Mountaintop bird life was sparse: I was a little surprised to find no juncos. A raven quorked along the way; a nuthatch didn’t seem concerned; a Pileated Woodpecker was rattling the doorknobs of a pine tree.

A little pressed for time and daylight, I followed the guide’s backtrack route, getting back to the car in 3:50, covering about 7.5 miles. My notes say that I covered a 8.3-mile circuit in 1995 in 3:30. I guess those were someone else’s legs.

The sun was burning off the morning fog, residue from our several days of rain, as we set off northwest on I-270 on this car-powered field trip, stopping at nearly a dozen places in the Blue Ridge and Ridge and Valley provinces. We were again led by the local naturalist community’s answer to John Malkovich, the equally intense, hyper-organized Joe Marx.

Our first stop was actually still in the Piedmont, in the parking lot of a Pier One Imports in Frederick, just down the U.S. 40 strip from the Barbara Frietchie restaurant. We looked at the Leesburg Member of the Balls Bluff Siltstone, a breccia composed of broken material from an alluvial fan under conditions similar (except for aridity) to those in the eastern edge of Death Valley. The boulders in the image were broken off from the bedrock and placed by construction activity.

In class lectures, we’ve just been introduced to the various metamorphic rocks, so the timing of this field trip was apt. Moving farther west into Frederick County and into the Blue Ridge province, we explored the formations that make up the South Mountain Anticlinorium: a metagranite; the Catoctin Formation (composed of epidote-rich greenstone, a metabasalt); and the Weverton Formation, a sandstone metamorphosed to quartzite. We checked out the Weverton at Gambrill State Park from the grounds of an amenity known as the Tea Room. Nice views. Bluebirds, juncos, and lady beetles greeted us at the park. Moving on to Boonsboro, we stopped for the Loudoun Formation (phyllite) and the Harpers Formation (shales and phyllite).

Continuing west, we entered the Ridge and Valley province. Our first stop was at the stone Wilson Bridge, built in 1819 by Silas Harry (and rehabbed in 1984 by LeRoy E. Myers) to carry the National Road across Conococheague Creek. Bedrock here is limestone and shale, and the creek follows the shale (lest it dissolve its bed of limestone). On the west side, up a short hill, are outcrops of the Pinesburg Station Dolomite (ca. 472 Ma) and the Chambersburg Limestone (just younger, 472-461 Ma). The dolomite, uptilted into almost vertical layers, laced with shale, is pictured.

Pushing on the last of the season’s acid-yellow maples, we came to the Martinsburg Formation, a fissile (breaks in your hands) shale interbedded with graywacke. This turbidity-current deposit was first named by Swiss shepherds as flysch. And then continuing past Hancock, we came to the Western Maryland railroad cuts. The railroad ran parallel to the C&O Canal. When the cuts were made in the rock, ca. the beginning of the 20th century, the intricacies of folding captivated geologists and the lay public. Now the rocks are heavily weathered, but you can still see the lines of synclines and anticlines. At right, the line of white aligned with Joe’s head is an intrusion (perhaps from groundwater) of calcite.

With the light fading, we wrapped up at the new poster child for geology, the giant road cut for I-68 through Sideling Hill. Even with the poor photographic conditions, the lines of the syncline (U-shaped) that form the top of the ridge are unmistakeable. Joe pointed out that it’s very rare for a ridgetop to be formed from an anticline (A-shaped), despite one’s intuition. Rocks stretched over the apex of an anticline break and quickly erode. Rather, what we observe is either a syncline (the rocks are compressed at the bottom of a fold and are somewhat more resistant to erosion) or a breached anticline (the apex is broken off), making two mirror-image ridges. Indeed, the whole of the South Mountain Anticlinorium is one such breached anticline, forming the Blue Ridge/South Mountain to the northwest and Catoctin Mountain to the southeast. The aha! of the trip was Anne’s, as she worked out just how immense the folded layers of rock would have to be to put the summit of Sideling Hill at the bottom of those folds. Our rocks here are the Rockwell Formation, and below that, the Purslane Formation.

After a gloomy, drizzly start, the wet weather held off and we had a great field trip, led by Joe Marx, exploring several sites of geological interest in the Four Mile Run and Holmes Run stream valleys in Arlington County and Alexandria City.

Setting out from East Falls Church Metro in the Piedmont, we paused to look at a cut in the stream bed of Four Mile Run to check out the alluvial layer from the last glaciation. The run slithers under I-66, skirting the so-called Brandymore Castle. At Joe’s fast pace, we climbed the castle, actually a lens of quartz from the middle Ordovician that protrudes into the landscape. The bedrock here is the Sykesville formation, a Cambrian schist, with bits of an even older actinolite intruding into it, and we found examples of both.

After a quick trip to Rosslyn to climb the first of five Tertiary period upland gravel terraces (the fifth and oldest forming the hill at Tysons Corner), we returned to Four Mile Run, farther downstream at the Long Branch Nature Center. We took a lunch break and indulged in some geology humor (Q: Where can you find the floodplain in Arlington County? A: Look for the picnic tables.) and did some sorting in the parking lot so that participants in Cliff Fairweather’s galls workshop got where they wanted to be. We stopped at Carlin Springs, now dry, but once a 19th-century resort stop on the W&OD railroad.

The high point of this stop was visiting a lovely cascade of Four Mile Run, relatively unmanaged and unchannelled, known as Hoffman’s Reach (sp?). Here the stream has carved potholes in the Cambrian-period Indian Run formation; granite intrusions into the pale gray rock are visible in the photos. Joe also pointed out a good example of the bedrock decaying into saprolite; a soil scientist, working top-down from the other direction, would call this the C horizon, which is quite thick in this area.

Our capstone stop was at the tiny sliver of a park in Alexandria named for Dora Kelley. Here, in the steep cut of a gully formed by a tributary of Holmes Run, Joe turned up an instance of the gravelly Potomac formation of the Coastal Plain (from 125 Mya) lying on top of the metasandstone of the Indian Run formation (from about 500 Mya). In the image, Joe is standing on loose gravel in the gully, and the rock exposure is behind him. The top horizontal edge of the dark, solid Indian Run rock is about even with Joe’s mid-thigh, and the layers of Potomac formation (gravel to clay) lie above.