Our new, improved methods of surveying are already paying off at Somme Woods. Somme is a Cook County forest preserve in Northbrook where a group of volunteers I’m part of has been carrying on a census of nesting birds for the past several years. Last year we identified 33 species as probable nesters, and we managed to find nests of 22 of those species, confirming their presence as breeding birds.
What we lacked in earlier years was a consistent, repeatable methodology that would let us make solid estimates of populations. You can prove that song sparrows nest at Somme by finding one nest, but figuring out how many song sparrows nest there is a more difficult problem, one that requires a systematic approach.
This year we laid out a grid of observation posts 150 meters apart. We visit them on a regular rotation, stopping at each for six minutes and recording all the birds we see and hear. I had thought that the grid would give us a level of scientific rigor we hadn’t had before and that it would make certain we were covering the whole place thoroughly and not missing any portions of the preserve.
These alone would be good enough reasons for adopting the grid system. Our results are respectable now. If somebody comes up with a plan to turn Somme Woods into a parking lot, we will be able to lay out hard data on the value of the place as habitat for a variety of birds, data that will have to be taken seriously because it has been collected by scientifically impeccable methods. We can also ensure continuity. When those of us who began the study pass to that great oak savanna in the sky, others will be able to take the binoculars from our faltering grasp and carry on the work without interruption.
But there have been unexpected psychic benefits for us as well. Our walks through the grid system are changing the way we think about the preserve. The portion of Somme Woods we are studying is bisected by a set of train tracks and by the west fork of the North Branch of the Chicago River, here channelized into a straight ditch. The tracks and the river run side by side through the northern half of the preserve and then diverge slightly in the southern half, the river turning straight south while the tracks continue in a southeasterly direction.
The river is, for all practical purposes, an impassable barrier for birders. So in our minds, Somme has consisted of two quite separate halves. We enter the east from a parking area along Waukegan Road and the west from a parking lot by the post office a half mile away, and we tend to think we are seeing two different sets of birds in the two halves.
But birds aren’t affected by railroad tracks or by rivers less than 20 feet wide. They move freely from one side to the other, and now, thanks to our grid system, we can plot the locations of singing males on maps and discover that the cardinal we heard from the west side on Tuesday is the same bird we heard singing from the east side on Wednesday.
Our grid system is even helping us sort out the crows. I had thought we would never be able to reduce the level of chaos in our superabundant population of crows. I expected we would just have to report that every time we looked up one or more crows were flying over, and that some of them nested here–possibly–and others nested nearby and either fed here or passed over on their way to and from feeding areas.
But now we are seeing crows forming pairs and driving other crows away from whatever patch of woods they have selected as their own. So far we have discovered two nests and seen another pair carrying nesting materials to a location we have not yet pinned down precisely. I think I have found at least two other pairs holding territories. We can now concentrate our efforts on discovering where they are building their nests.
We have at least 15 male song sparrows singing on territory at Somme, and almost as many cardinals. I’m really amazed at these numbers. I knew these birds were common, but I didn’t think we would have nearly this many. Robins are also all over the place. We have both residents and migrants passing through, so it is hard to get a handle on numbers. So far I have seen one bird building a nest in the oaks in Vestal Grove, but if we have 15 nesting pairs of song sparrows, I would bet we will end up with 20 pairs of robins.
Last Saturday evening just after sunset I took a look around the largest of the Somme prairies, an area that measures about 300 by 400 meters and occupies the western end of the preserve. It’s actually only partly native prairie. The rest is a bastardized grassland full of imported weeds, a Eurasian meadow. But birds in general don’t seem to concern themselves with the presence or absence of particular species of plants. Our prairie songbirds will nest quite happily in Eurasian meadows if that is all that is available.
We had been seeing some eastern meadowlarks in this big prairie, but they apparently moved on about the first of this month. There doesn’t seem to be any good reason for them not to nest at Somme, but so far it hasn’t happened.
I was out there last Saturday night hoping to hear some woodcocks displaying, and I wasn’t disappointed. I heard five birds. Four of them were along the border between the prairie and the woods, which is where I expected them to be, but one was way out in the middle of the open grassland. That was a surprise. But there is a bit of brush along the fence that marks the western boundary of the preserve, and it could be that any female attracted by this bird’s display could find a suitable nesting spot there.
Our pair of resident red-tailed hawks seem to be moving back into last year’s nest. I see one or both of them soaring, usually accompanied by a harassing escort of crows. Of course flying crows are usually escorted by redwings pecking at them. It’s like the reverse of those drawings of progressively bigger fish swallowing smaller fish. Here we have progressively smaller birds harassing bigger birds.
In other news on the bird-of-prey front, we have a pair of kestrels hanging about the place. These small falcons nest in holes in trees and like to hunt over open areas, so Somme ought to be ideal for them. We have standing dead trees all over the place, some with natural cavities rotted into them and some with woodpecker holes.
I also found a pair of white-breasted nuthatches creeping over the trunks and limbs of the big oaks in Vestal Grove. White-breasted nuthatches are a common woodland species, but so far they haven’t nested at Somme. They are another hole-nesting bird, so we can hope.
Hopefulness is our most consistent state of mind at Somme. We all are developing a rooting interest in the bird life of this preserve. “C’mon nuthatches!” “C’mon kestrels!” “Nest, nest, nest!” I feel like a combination cheerleader and real estate salesman. “Let me point out to you the advantages of this wonderful location: a rich selection of choice nesting holes, a diverse insect fauna, a burgeoning population of small rodents. Your kids will love it!”
And I feel a little bit competitive. I want to discover better birds than surveyors of other preserves. I want to smirk smugly next September when I tell people how rich and rare my birds are.
We are also picking up information on Somme’s mammal life. The deer are everywhere. On average I’ll see eight to ten animals in a two-hour visit. They are ridiculously tame. I’m told people come out and feed them, and they often act like they expect me to hand them a piece of bread. Animals will approach me while I am doing my six-minute stand at an observation post. They aren’t quite tame enough to walk up and let me scratch them behind the ears, but they are getting close. Somehow I think it just ain’t right for wild animals to be that tame. It ought to be harder to see them. A good look at a deer ought to be a reward for skill in stalking and not like a visit to the zoo.
I suspect that the great coyote invasion has reached Somme. I haven’t heard or seen any yet, but I am finding very fresh deer carcasses that have been expertly eviscerated. I suppose this could be the work of raccoons operating on animals already dead, but I don’t think so.
The absence of foxes may also be a sign of the arrival of coyotes. Dens where the smell of foxes was once strong now seem abandoned. Coyotes are unlikely to ever destroy a prey species such as deer, rabbits, or woodchucks, but they might well eliminate a smaller competitor. The success of coyotes in invading northeastern Illinois could be a catastrophe for our native foxes.