Aging Tracks

by Carl Strang


Yesterday  I made several references to how changes in weather conditions were affecting the footprints made by skunks over two successive nights. Awareness of weather is an important aspect of estimating the age of tracks, no matter what surface they are in. I’ll probably expand on this in the future, but for now let’s take a closer look at those skunk tracks. We’ll compare photos of skunk tracks that differed in age by one day. The first is of a footprint made the previous night (and thus a few hours old).




It is an isolated track, made where the crust had not fully formed as explained yesterday. I hope you can see that, while the footprint does not have a lot of internal detail thanks to the large-grained, partly crusted snow, the track does have fairly sharp edges. The next photo is of tracks that had been made two nights before.




Then, as explained yesterday, a crust had not formed, so all footprints show. But thanks to the sunny, relatively warm conditions the next day, some melting had occurred. Not only was the internal detail of the footprints lost, they had collapsed somewhat and their edges became rounded. These are events that mark the aging of footprints in any substrate. With experience, and keeping recent weather conditions in mind, one can become increasingly skilled at aging footprints. If you cannot see much difference in the photos, don’t be concerned. The differences were easy to see in the tracks themselves.

Skunk Walkabout and Snow Crust

by Carl Strang


The cold front that came through over the weekend left us with some drifted snow and cold temperatures, providing for a few more days’ tracking. Monday night the skunks were on their mating season walkabout, and as best I could tell with the patchy snow cover, 4 individuals were active on Mayslake Forest Preserve.




One, apparently the skunk whose den was featured earlier in the month, covered nearly all the preserve and overlapped trails with three others in different portions of Mayslake’s periphery.




Though not yet crusted, the snow was not deep in most places, and was wind-packed, so the skunks did not have too much trouble (though as you can see in the next photo, the skunk had to down-shift to a diagonal walk gait where the snow was a little deeper).




Tuesday was warm and sunny. As mentioned earlier, such days in February typically are followed by cold nights that freeze the partly melted snow surface to form a crust. The heat rises into the open sky, but where there is insulation above even from leafless branches the crust forms more slowly. The skunks were out again, this time on crust, but though they were supported in the open they were breaking through under the canopy.




In the above photo the skunk was moving under the edge of a willow’s thin cover, so that some steps (circled) broke through while others were supported. This is how you may find where an animal seemed to be drifting or skipping through the air, touching down only at intervals so as to leave isolated footprints.

Canada Geese Return

by Carl Strang


It has been about a month since I provided an update on my monitoring of Canada goose winter roosts in DuPage County. Then, all of the major roosts except the one at Hidden Lake Forest Preserve had frozen over and been abandoned. In the first half of February, pairs of local geese began visiting nesting sites, beginning to stake their claims for the coming season. Such behavior does not significantly affect the roosts, however, as nearly all the birds continue to use these at night. By mid-month, with the weather having become more seasonable, geese were a common sight again. On February 15 I found both the Blackwell and McDowell roosts open again. There were plenty of birds, 2000 and 200 geese, respectively, though these counts were below peak levels observed earlier in the winter.




A week later, on the 22nd, both roosts were back to the levels I had seen earlier in the season, at least 3000 at Blackwell (above) and around 500 at McDowell (below).




In both places the recent resurgence of cold temperatures confined the birds to smaller open-water pools within the otherwise iced-over roosting areas. Over the next few weeks I expect the roosts to begin dispersing as waters open up again and the nesting season begins. Local birds already are scoping out their territories, as mentioned above, and northern ones will race to claim favorite nest sites in the Hudson Bay region.

Canada Goose and Cackling Goose

by Carl Strang


A few years ago the decision was made by the American Ornithologists’ Union (AOU) to recognize a split of the Canada goose into two species. For a long time it has been recognized that Canada geese across the continent form distinct races, distinguishable by nesting geography, body size and proportions, and sometimes minor color variations. They were regarded as all belonging to the same species, however, meaning that the races were really interbreeding or potentially interbreeding populations.


One huge physical difference exists between the tundra-nesting varieties and all the rest, however: body size.




The several tundra nesting races, one of which is represented by the birds in the left side of the above photo, are much smaller than more southern varieties as in the birds on the right. The separation by habitat is severe, and the size difference as well, so for the moment there are two recognized species. The little ones are called Cackling Goose officially, while the big ones retain the name Canada Goose. It is possible that there will be further splitting in the future.


We see cackling geese here in migration, and sometimes over the winter. At the Blackwell roost I saw a pair early in the winter, but have not spotted them since (though after that roost grew to 3000 birds it would have been easy to miss them). One little bit of my winter behavior study will be to watch out for cacklers and see whether they behave differently from their larger relatives. I will post an update to that study tomorrow.

Great Horned Owl Nests

by Carl Strang


The second half of February is, for me, the time for an enjoyable annual ritual: the search for the great horned owl nest. Last weekend I found the nest at Fullersburg Woods, and a few days ago I found the one on Mayslake Forest Preserve. Since Mayslake is the preserve I am monitoring these days it was my main focus, but I have followed the Fullersburg pair for several years now, and wanted to see if they stuck with the pattern they had shown in the past (a preferred part of the preserve, and a preferred nest platform type).


Great horned owls are fairly big birds. They prefer a solid platform for their nest, and they don’t build a nest themselves. This narrows down the possible sites. Common alternatives are to use a hawk nest from the previous season, or to find a large tree cavity. They also are known to use buildings and artificial platforms.




See that glare? I call it the hate stare of the incubating owl. They don’t want you around, and while I violate that preference by actively seeking the nest, once I have found it I minimize visits and don’t broadcast nest locations widely.


These are fairly common birds, and if your favorite woodland has a pair you may want to seek their nest. It involves a tree-by-tree search. Focus on the largest trees, consider the size of the birds and their preference for a solid foundation. Sometimes not much is visible. The first great horned owl nest I ever found, some years ago at Willowbrook Forest Preserve, was visible only because one feather tuft on the incubating bird’s head could be seen through the entrance to a depressed tree cavity. Especially difficult to find are nests in dense spruces or other conifers (there are a lot of these at Mayslake!). To narrow the search, focus on areas where you have seen the birds during the day in the winter, and locations where the owls are calling at night. If you fail to find the nest, try again in late March or April. By then the young have hatched, forcing the adult to sit higher when brooding them. But view from a distance, preferably using a spotting scope if you want a detailed look.


This year, for the first time I know the locations of nests on adjacent great horned owl territories. Mayslake and Fullersburg are separated by the Route 83 corridor and a residential neighborhood. GoogleEarth has a nice ruler feature that I used in measuring forest blocks in the periodical cicada study . Here I was able to measure the distance between the two nests: 1.07 miles. That distance would allow the mathematically inclined to compute an estimate of the number of pairs of great horned owls in DuPage County. As it is based on only one data point it would lack statistical validity, but it would in any case be an overestimate as most parts of the county are not so well suited for this species (commercial areas or residential neighborhoods lacking big trees also will lack great horned owl nests).

Mink Dossier

by Carl Strang


Last weekend I paid a visit to Fullersburg Woods Forest Preserve. I was surprised to find mink tracks, representing at least 4 individuals, all over the preserve. In the three years my office was there I had seen tracks only once or twice per winter, with only one individual in each case. Today I thought I would share my entire dossier  on that species. Here’s a photo of the critter, then on to the dossier.




We saw them frequently in daytime when floating the Tippecanoe River in Indiana when I was a child. Usually they ran along the shore or appeared in drift snags. Occasionally one dove under the water. I first identified the tracks at Fullerton Forest Preserve in 1985. Five toes each foot, very round appearance in sand or mud, larger than one would expect for the size of the animal (paddle feet for swimming). Winter tracks in snow at McKee Marsh, Blackwell Forest Preserve, early 1986: nearly all in trot or lope patterns (actually a bound with offset feet). Dropped to straight bound once when passing through an area of deeper (6-8″) snow.

25MY86. One observed traveling through a small, cattail-choked waterway at Herrick Lake Forest Preserve. Moving, body seems to flow, even on dry land. It saw me, turned around, and after going back upstream 10 yards or so climbed back over the embankment that separated the smaller waterway from a larger marshy area.

28NO86. At Culver Fish Hatchery:




11JA87. Waterfall Glen Forest Preserve, Sawmill Creek near mouth at Des Plaines River. Mink dug leopard frog up from somewhere beneath trunk of fallen tree resting on bank. Mink carried frog on a twisting path before digging hole in the 8″ snow and depositing the frog without filling hole. Frog not yet frozen, tracks very fresh. Tracks restricted to area around that tree, with many burrow-like holes entered. Mink has shelter there or else emerged from and entered river under tree roots.

21JE87. Tracks crossing muddy road at Herrick Lake Forest Preserve. Photos: in first picture, left track 1.125″ long x 1.25″ wide, right 1.375 long x 1.25 wide. Stride ~13″ in bound. In second picture, front? definitely smaller, hind? aligned more with previous set. If front’s supposed to be larger, animal turned right. In drawings, #1 1.125W x 1.25L; #2 1.25W x 1.125L; #3 1.25L x 1.125W; #4 1.25W x 1.0625L.



27JE87. I was picking chickweed in a rank patch at McKee Marsh at about 9am as a mink passed. It was so buried in the chickweed I thought it was a woodchuck, but it seemed to be shaking plants less and making less noise than I would expect, and moving faster. Caught glimpse of its hindquarters and tail. Had passed within 5 feet of me as I stood still. Was moving toward woods, away from marsh, ~40m from marsh.

16JA88. In shallow snow over ice of river, mink did much bounding in travel (mostly). In bound may lead with one side so that some tight “lopes” are actually bounds. Several photos to illustrate this, after fox trot photos. Photos of mink gallop. Sets 2 feet separate, and each set well spread out (bounds on the same ice were 16-18″ apart).

17JA88. See meadow vole entry.

23JA88. McDowell Forest Preserve. Mink trail wound in and out of fence row along edge of brushy/small tree area and grassy field, with some sorties into either but no more than 10m from boundary. Once went down burrow, once apparently slid on belly. Last photo on roll shows separate front and hind feet (otherwise mainly bounding with hind feet landing on fore). FF ~1.125 x 1.125, HF ~1.5 x 1.25W. Entered and exited several more holes. Eventually went into the river. These tracks were made early last night: some in water that later froze; also, I had noticed crystals had formed in tracks, when I tried to blow snow away. Backtracking: had climbed into low (3′) crotch of large willow, crossing to the other side before jumping down. A tangle of trails where a very small stream (6″ wide) flows into river. If the mink I had followed went no farther, its evening home range included ~0.25 mile of shoreline and inland up to 100m.

I picked up another trail consistent with age of first, and followed it back inland, through logs, in and out of holes, etc., until it led to where mink had pulled out of water, on other (N) side of parking lot. Toward end, at least, mink mostly led with left side, though it sometimes led with right.

13FE88. I spotted mink tracks from U.S. 31 between S.R. 110 and Rochester, IN, got pictures. Had tunnels and slides.




15JA89. A mink at Herrick Lake Forest Preserve was dragging something, sometimes leaving only a thin mark atop the bounding set, sometimes a wider (3/4″) mark that was continuous between and over sets. The mark was on top of the tracks, therefore following them, but was on the right side while the hind feet were on the left, implying that the marks weren’t made by the tail. (See red fox 19DE89). Last month at McDowell, I found where a mink had apparently dragged something for a considerable distance, but this time the dragging was continuous and the heavy mark was more than an inch to the left of the bounding tracks. In both instances the animals were moving along the edge of a frozen lake, on the ice.

6JL90. At Hidden Lake Forest Preserve, the largest mink I’ve ever seen, moving from a perennial-old field area backed by forest into the new large marsh area.

5AU95. Red River, WI, near kayak put-in. Mink hunted along shore, on land, within 8 feet of water, moving downstream. Sniffed ground, looked into vegetation. Sometimes stopped, sometimes diagonal walked, sometimes bounded, covered 150 yards of shore before it caught a large crayfish and carried it inland. Chipmunks responded as they did to red fox at Arboretum.

8AU98. Red River, WI. Across from lunch area at first drop: beneath a group of river’s edge white cedars was an old stump with a 4″ hole. Nose of my boat touched a foot away from it, and a mink’s head appeared. I sat still and watched it for more than 3 minutes. It mostly sniffed, looked around, yawned a couple times, stepped its front legs out to sniff my boat, ducked back in a couple times.

30OC99. Dead mink, not dead too long, red blood still around mouth but no other sign of damage, on a mudflat near a stand of cattails at Fermilab. Internal injury, or self-biting during convulsions associated with illness?

21FE99. In the 3 days since the last snow, no mink tracks at McKee Marsh. Was the dead one at Fermi last fall the sign of a diseased, crashing local population?

14OC00. A mink seen at Fermilab, not far from the location of last year’s dead one. 80 yards from water, in upland old field.

31AU01. Algonquin Park, Ontario. A small one, probably an adult female, using the boardwalk of the Spruce Bog Trail, in the bog, to travel on. I was standing still, she did not notice me until 15 feet away, then turned around, went back a few steps, and got off the trail into the bog, disappearing quietly into the dense vegetation. When hunting, she sniffed frequently, and occasionally looked to the side.

20AU05. A mink and I startled one another in the early afternoon as I walked the pond in my dragonfly monitoring route at Songbird Slough. It made a brief loud squalling sound as it turned and ran away, a sound very similar to that made by a complaining juvenile raccoon.

4SE06. A mink visited my camp on the last night of my Georgian Bay sea kayak trip. I was able to get some photos.




14FE09. Fullersburg. Mink tracks are all over the preserve on the morning after a 1” fresh snow over bare ground. There appear to have been 4 individuals active last night: 2 traveling together between Sycamore Peninsula and the York Road bridge, one on and around Willow Island (on both sides of Salt Creek), and one in the west part of Butler Woods. This is in marked contrast to the rare observations of single individuals at Fullersburg over the past three years. Recovering from decimation by disease?

Mastodon Camp

by Carl Strang


Over the past two summers I have had the opportunity to participate in a paleontological dig at Pratts Wayne Woods Forest Preserve in northwest DuPage County. This excavation, conducted by the Forest Preserve District of DuPage County and the Field Museum of Natural History, was prompted by the discovery of three mastodon molars and some bone pieces during wetland restoration work.


Photo courtesy Forest Preserve District of DuPage County

Photo courtesy Forest Preserve District of DuPage County


The dig is being structured as an education opportunity for area residents. Teachers and high school students have been the core participants in the first two years. There have been tours, presentations and half-day dig opportunities for members of the general public.




During the first summer, the main products were large numbers of small tusk and bone fragments.




In 2008 the digging revealed some small buried trees.




Wood samples are being analyzed, but two black spruce cones were found among the trees.




As I mentioned in my account of last fall’s glacier retracing trip, that tree species no longer grows this far south, but was here in this mastodon’s time 11,500 or 12,000 years ago. These paleobotanical discoveries fill in some of the picture of the local environment as local climate warmed after the glacier melted away.


With the major bones still waiting to be found, there is plenty of motivation to resume the dig when circumstances permit.

Fullersburg Archeology: Closing the CCC Chapter

by Carl Strang


Visitors to Fullersburg Woods Forest Preserve experience works created by the depression-era Civilian Conservation Corps whether they know it or not. Most of the trails, the parking lot, bridges, dam, visitor center and trail structures were created by workers in the Fullersburg CCC camp. I have shared some of the ruins of other works that no longer are in use, and want to close the CCC chapter with a few more.


The 1937 map that has been our guide to CCC projects shows a number of latrines and “incinerators.” Some of the latrines still are in use, though updated and maintained by the Forest Preserve District. I provided directions to ruins of a latrine and possible incinerator yesterday . Now I want to cover the rest.


We’ll start at Willow Island, which itself probably was created by the CCC , reached by taking the trail north from the Visitor Center and crossing the little bridge.




On Willow Island, the still standing structure at its southeast corner is a picnic shelter, the one on the east side held a well. The spot marked “Incinerator” in the center of the island is our first ruin, a hollow cube of concrete set flush with the ground and bearing 3 holes broken in its top.




A short distance north of that cube is a rusting wire cylinder that once may have been the actual trash burning container.




Please remember not to disturb any artifacts you may find. The figure-8-shaped large channel in the southeast part of Willow Island was dug after the CCC was done, in a since abandoned attempt to provide an area for wildlife viewing.


Crossing back over the Willow Island Bridge and turning west to follow the trail around the Interpretive Trail river bend, you will pass a pump not marked on the map, a tiny shelter, and the functioning latrines shown on the 1937 map. I could not find a trace of the adjacent incinerator. The original support beams of the shelter at the northeast corner of the river bend were rotting, and replaced by octagonal planed beams in 2007. Our next ruin is one of the latrine vaults near the north end of the bend.




I could find only one in the area marked, but tall dense growth of garlic mustard and dame’s rocket obscured much of the ground that day.


We finish in the area of today’s buildings around the north end of the parking lot. Well #2 is not there, as far as I can see. There is an old broken concrete slab where an Incinerator is marked on the 1937 map, across the service road from the west end of the garage. 




That concludes our archeological adventure for now. The next chapter will take us into parts of the preserve that were added after the CCC era. But in our current time of economic uncertainty there is something to be said for exploring works that date back to a period that historians still call the Great Depression.

Fullersburg Archeology: A Former Picnic Area

by Carl Strang


Today I want to plant another idea for those who might wish to search out archeological ruins from Fullersburg Forest Preserve’s past. This might be a good expedition for late winter or early spring, after the snow has melted and before the woody plants leaf out. The ground might be wet or muddy in that season, so footwear should be selected carefully. This can be done on a warm sunny summer day, too, but leafed out shrubs will make the search more challenging.




In Fullersburg’s early heyday after the improvements made by the Civilian Conservation Corps , there was a picnic ground in the triangular area on the east side of Salt Creek, just downstream from the Visitor Center Bridge and across from Sycamore Island. The most conspicuous surviving structure is a grill or incinerator.




It is located close to where an unlabeled circle is marked on the map, northwest of where the labeled incinerator was crossed off (is this the relocated “incinerator?”). One of the latrine vaults still can be readily found.




If there was a second one, it is more obscure. Someone thoughtfully placed a log in it to ease the escape of any animal that might fall into the hole. Existing, but a little more challenging to find, are the ruins of the Shelter and Well #1. The shelter was at the northwest corner of a relatively elevated area, and must have provided a beautiful view of Salt Creek. Today all that remains are scattered bits of stone and concrete at the surface of the soil.




South of there, Well #1 no longer bears its shelter, but remains as a square of concrete with the circular center pump mount still in place.




Tomorrow I will conclude the CCC chapter of Fullersburg’s history.

Fullersburg Archeology: Major CCC Works (?)

by Carl Strang


This entry on the Civilian Conservation Corps  chapter of Fullersburg Forest Preserve history is more speculative than the others, hence the question mark in the title. These are relatively large scale changes in the landscape, and documentation I have been able to find is limited.


The first stop is the most certain. The camp itself was located on the site of the present day Hilltop Prairie, west of the parking lot and buildings.




I suspect that the camp extended north of the prairie proper onto more level ground. Below that prairie to the north is the Amphitheater, annual home of a stop on Fullersburg’s Halloween Nature Walks.




The Amphitheater’s location coincides with a symbol on the CCC’s 1937 map (oval shape in the center of the excerpted map piece below).




This symbol on a topographic map usually represents a “cut,” a place where earth was excavated. This suggests that the Amphitheater is an artifact, perhaps created by the CCC themselves. An old newspaper clipping in the Forest Preserve District files says that performers (a singer, Elsie Janis, specifically mentioned) came from time to time to entertain the workers in a theater. The Amphitheater bowl, located immediately below the camp, seems the likely location of this theater.




Bits of retaining wall, some of which have been buried by slumping or erosion, persist in and near the Amphitheater, and likely were installed by the CCC.


Channels creating Willow and Sycamore Islands, along with two smaller islands west and northwest from Willow Island, are supposed to have been dug by the CCC as well.




These islands do not appear on the original 1840 survey sketch or on the 1874 DuPage County atlas, but they are clear in the 1937 map



and the 1939 aerial photo.




Thanks to siltation the channels have narrowed greatly and become shallower since that time, the smaller islets now are attached to the mainland except in times of flood, and Sycamore Island is now Sycamore Peninsula except in high water. The bridges over Salt Creek at the Visitor Center and the western extremity of the preserve (i.e., Rainbow Bridge), as well as the bridges providing access to Willow and Sycamore Islands, bear the marks of CCC work, their construction involving use of the same kinds of dolomite slabs and beams as the Visitor Center and many of the trail shelters.

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