Kurt shared another great write-up from his Loudoun Bird Atlas explorations – check out this latest entry to see what great birds he encountered:
The weather report for last weekend was hot & humid – a return to the “normal” conditions of other past July’s in Northern Virginia. I tried to get out early, but its sooo… hard what with wanting to add some extra sleep and all after the usual weekday toil. Jan Frye joins me on Saturday morning – her first atlas outing. A spirited and skilled novice, she can find birds which is always welcome when one does atlases or counts or such. We arrived close to 7am at RoundUp Ct, just east of Aldie (part of the block known as Middleburg 2), with a plan to upgrade previously found species as we continue westward. This day, I hope to get to the Blue Ridge by mid-morning, as I have some access points to the forest there.
We quickly see a juvenile Red-shouldered Hawk. I had heard a juvie nearby a couple of weeks earlier, along Tail Race Rd, and I am sure it’s the same bird or a nest mate. A wonderful bird to gaze upon, its perched in a tree near the road and follows our car’s movement intently. It flies away once we get within 30 yards or so. We head for a spot that had Prairie Warblers last week, where the medium-aged Red Cedars meet some bushes along an asphalt road spur. Jan quickly notes a singing Prairie on this spur and we go to foot. The warbler moves from cedar to bush and in-between, chipping incessantly – I am sure young are nearby but we see only the adult male. Nearby, a Gray Catbird flies into the same brushy edge surrounded by the Red Cedars – and towhees call nearby. With hardly a sound, a White-eyed Vireo appears, making soft cat-like whines until another comes to it for a brief moment – then parts as the food is delivered to its waiting mouth. Unfortunately, the young Prairie Warbler is not nearly as cooperative, so we move on after about 20 minutes.
We head over to Tail Race Rd which has a few potential breeders to add to the atlas, such as Grasshopper Sparrow. We quickly spot one of the sparrows on the wooden rail fence and set the scope on it. It only sings today, moves into the field, then back to fence &tc. Fortunately Jan notes an Eastern Meadowlark perched up on a nearby bit of weed with something in its bill. The scope lets us see the food item and thus the species is confirmed for the block. Very nice.
The question often arises, how can one can confirm any bird as a breeder, what with the sheer serendipity of actually finding a particular representative doing something like carry a food item, or nesting material. But, as us geeks like to exclaim, “it’s a numbers game” which is another way to say it all boils down to statistics. Let me explain. There are large numbers of birds of many species in the block we atlas and so finding any of them doing a “breeding thing” is not that much of a stretch.
Consider Northern Cardinals. Beautiful birds and quite common in our area, most often found in edge habitats with bush components. I know there is at least one pair in my backyard neighborhood adjacent to Huntley Meadows – this location has an area of about 1-2 acres. To estimate the breeding density in Loudoun County, I examined the USGS breeding bird survey (BBS) data easily found on the net. The appropriate Loudoun County BBS route is known as Taylorstown – which produced an average of 42 Northern Cardinals each year. Now these BBS data derives from 50 stops where the volunteer counts everything that moves or peeps at each one. And, a good observer can detect birds at 100 yards or more. So, each stop covers an area of over 6 acres. Which means that, on average, there are about 0.13 Northern Cardinals per acre (or, about a 1 in 8 acres) for the Taylorstown route.
Using the 1 in 8 acres figure, you can see that for the 10 square mile Loudoun atlas blocks that are being atlased, the estimated number of Northern Cardinals in a block is 800. Considering that these birds are all busy doing breeding activities in May, June and probably July, then it’s no wonder that these birds are one of the species most quickly confirmed per block in the atlas. But, the really neat thing is that American Robins, Eastern Bluebirds, Gray Catbirds and Chipping Sparrows have similar population densities. And so, these species are also relatively easy to confirm as breeders.
The numbers game really wins out
We head west, eventually arriving on Willisville Rd in the block known as Bluemont 5. This spot has had a Willow Flycatcher for several weeks. We watch and wait. I walk a nearby field edge as a Field Sparrow has been present – I hear the Willow Flycatcher so turn about, retracing my steps. Jan is watching from the other side of the habitat. We both see and hear the Willow as it flies across its territory – a small patch less than an acre in extent (maybe half an acre). Willow trees and other deciduous kinds edge the side Jan is at, near the corn field; the other side – on which I am located – is a hay field. Across the road, another hay field. The ditch is wet, and a wet swale runs through the habitat preferred by the Willow – bushes, grasses and a short tree (and popular singing spot for many of the residents such as Song Sparrow, Common Yellowthroat, and Brown Thrasher). The Willow flies across and it looks a bit odd – Jan notices it first, food in bill. A close look reveals a largish black bug. It flies across to the Willow Tree edge, carrying the bug while emitting soft “wits”. And we leave with a nice confirm for breeding.
We make it to the Blue Ridge near mid-morning. We visit a backyard of a helpful resident. Chipping Sparrow is singing in the yard and a nest with 2 young Eastern Phoebes is under the eaves of the house. Down the road, we visit another area and move up several species to the probable designation as towhees, Wood Thrush, and American Redstarts are singing in the same spots as last week. What is surprising is that both Brown Thrasher and Gray Catbird are in the forested area, too.
Near noon, and with other responsibilities calling, we head home.
I return the next day, arriving at the blue ridge location near 7 am. I am lucky – an Eastern Screech Owl whinnies a few times, unseen, perhaps a 100 yds away. It takes about an hour of exploration to find a Red-eyed Vireo nest with 2 young in and one standing nearby. I think these birds are running 1-2 weeks behind piedmont breeders. I spot a hummer (female) up here and the Rose-breasted Grosbeak makes a return show, this time I spot the male looking quite bright. But the real payoff lay nearby – the chips I heard last week I here again today. I wait and look, go away and come back. Finally, I find the birds. Worm-eating Warblers, one in the lead and the other following, occasionally opening its mouth. A really surprising breeding confirmation. Nearby, I finally hear the male softly trill the song. Yes…..
Heading down and east to where the foothills meet the piedmont, I visit a few roads and upgrade potential breeders. I lucked into 2 Eastern Wood Pewees on a tree limb over a driveway, making very loud begging noises. It’s getting late in the morning and by 11 I come across stretches with very little activity – yep, the heat is on. I find that when it gets hot, bird song and activity greatly decreases. I continue east, trying a few spots here and there, but failing to find any new breeders. My last stop is Tail Race Rd, arriving after noon, and I hear a Blue Grosbeak calling from a wooded edge near the road. I stop and after a few minutes of looking find it with a fledged bird.