Tracking Story: Sawmill Creek Mink

by Carl Strang


This snowy winter brings to mind an experience from several years ago. I was at Waterfall Glen Forest Preserve, wading through snow to follow the informal trail along lower Sawmill Creek between the railroad tracks and the Des Plaines River.





I came across some fresh mink tracks, and they were unusual. Can you see why?





This mink is in the diagonal walk gait. The normal gait pattern for mink is the bound, as introduced in an earlier post. When an animal is out of its usual gait, something interesting may be happening. Not only has this mink shifted down to the slower gait, there are drag marks. I followed the tracks, and they led me to a hole in the snow.




Noting the blood drops, I excavated the hole a little, and there was a leopard frog.




The frog was still wet and soft. It was so freshly killed that I thought it likely the mink had heard me coming and quickly stashed its prey. I backtracked, found where the mink had dug the hibernating frog out of the mud at the edge of the creek, and went on my way so the predator could retrieve its meal.


by Carl Strang


Nature Inquiries is about providing examples and methods of scientific inquiry that are accessible to anyone who wants to invest some time and thought in developing and answering questions about nature. I have in mind the person who, like me, enjoys exploring outdoor settings and wants to learn more about them, but doesn’t have the resources or background to engage in full-blown formal studies.




As such, we can afford to relax and open ourselves to the many little joys and side trips that may offer themselves along the way. One of the most important of these is the experience of beauty.




A lot has been written about beauty, but it all seems to boil down to the conclusion that beauty is an experience, rather than a quality of some piece of the physical world. It is “in the eye of the beholder,” and has no existence apart from our experience of it. And yet, we often find a common agreement that this or that object or scene is beautiful.




We are whole beings. The questions of our inquiries may engage our minds, but the beauty we find along the way is properly regarded as a more emotional or even spiritual experience. At the same time, the patterns we discover in our inquiries, the answers we turn up, paradoxically inspire feelings that are very close to, if not the same as, the experience of beauty. In my view this is a valuable outcome, side product, and ultimately motivator for those of us who are driven to go outside and explore the many mysteries that surround us.




In other words, there is no need to become so narrowly focused on an inquiry that we lose sight of the opportunities to experience beauty. I have attempted to illustrate this on a regular basis in this blog, and will continue to do so.

Fullersburg Archeology: Structures Still in Use

by Carl Strang


Today I want to continue reviewing the Civilian Conservation Corps chapter in the history of Fullersburg Woods Forest Preserve, this time focusing on some structures that still stand.


I’ll begin with the single remaining “Trail Shelter” marked on the 1937 map. Earlier I described some of these shelters that today are represented by only a few foundation stones. The standing one is very simple, and you can find it by traveling north from the Visitor Center, turning left just before the Willow Island bridge, and looking on your right.




This is simply a bench with a roof.


I long was puzzled by the different forms of shelters, sometimes so close together as to question what the builders had in mind. The map made this clear, however. Some of these structures have substantial beams and are larger.




They come in various shapes, but have in common the large round beams, which were formed from the trees that were cut to create the main parking lot, and the dolomite stone slabs, which came from the Lemont Quarries. All are simply marked “Shelter” on the map, and apparently were intended for picnics and other group activities.


The other common trail structure design has a square shape and smaller beams with square cross sections.




These are marked “Well” on the map, and originally contained pumps. Their frequent proximity to the shelters is explained as the provision of a water source for picnickers. None of these house pumps today.


The most substantial building left by the CCC is the Visitor Center, which they intended as a “Boat House”




In Fullersburg’s heyday as the most popular property in the then much smaller Forest Preserve District of DuPage County, this building was known as The Landing and indeed housed a boat concession from which people had excursions on Salt Creek.




It likewise is characterized by the use of large round beams and dolomite slabs in its construction. The CCC did a lot more at Fullersburg. Stay tuned.

The Trot Gait

by Carl Strang


The gaits I introduced earlier  were the basic ones, used by most mammals as they travel. There are others, however, and today I want to feature the trot. A trotting animal steps with its left front and right hind feet simultaneously, then its right front and left hind. The speed is faster than a diagonal walk (in which the animal moves only one of its feet at a time), so the footprints are farther apart. I have noticed two different patterns most commonly associated with the trot.




In the above photo, a coyote passed through a parking lot in the trot gait. Coyotes show this gait more than our other wild mammals (technically the opossum walks in a slow trot, but its peculiar footprints form the gait pattern of a diagonal walk). The footprint pattern of this coyote’s trot is unlike those in the gaits introduced earlier. The tracks appear to be in pairs, as was true for the diagonal walk, but the feet land farther apart. Furthermore, the hind foot is landing in front of the front foot.




Here is a closer look at one of those footprint pairs. In coyotes and other members of the dog family, the front foot is larger than the hind foot, and its heel mark is much wider. The heel of the hind foot has more of a circular shape.


A different trot pattern you may find is this one, provided in this example by a dog.




At first this pattern resembles the diagonal walk, but the pairs of footprints are too far apart, the tracks in each pair are too much side by side (rather than one slightly in front of the other with more overlap), and a close look reveals that all front footprints are to one side (to the animal’s right in this example), and all hind footprints are to the other. This puzzled me until I saw a dog producing the pattern. It was trotting, but as it did so it held its body at an angle to its direction of travel, so its front feet always landed to one side of its hind feet. Sounds odd, but if you watch enough dogs you’ll see it.

Bird Bath

by Carl Strang


Birds have been transients for the most part at Mayslake Forest Preserve this winter, as I have noted . A few days ago, during a break in the weather that brought temperatures up to freezing, there were a lot of birds on the preserve. It was striking to see robins, starlings and waxwings bathing in the frigid water of the stream just below the Mays Lake outlet.


Robin, cedar waxwing and starling bathing

Robin, cedar waxwing and starling bathing


For me this icy bathing underlines how incredibly tough these tiny animals are, to survive and even thrive in such an extreme winter. Elsewhere, members of the same three species were on the roof of an outbuilding beside the mansion, sipping the warming meltwater that was accumulating in little catches among the shingles.




Some waxwings also were picking at the snow higher on the roof. I could not see what they were after.




Such beautiful birds they are! Some of their colorful features have functions beyond species recognition. The red tips on the secondary wing feathers of some individuals (which led to the species name, as those tips resemble red sealing wax) have been shown to increase in number with age, and are correlated with rank in the social dominance hierarchy (pecking order) of the flock. The bright yellow band around the tip of the tail is the sort of thing commonly seen in flocking birds on the tail or back part of wings. It is called a “follow-me” signal, making it easy to keep track of the bird ahead when visibility is poor.

Food Chain

by Carl Strang


In an earlier post  I mentioned that I think food chains are abstractions. While that is true, sometimes you find one in more concrete terms. I ran into an example at Mayslake a couple days ago. Here is a place where cottontails have gathered in recent days to eat the bark from a tree branch that had broken off under the weight of the snow.




Forest Preserve District Plant Ecologist Scott Kobal provided an assist on the tree’s identification. The strange buds threw me, but I probably had been taught to identify the Siberian elm decades ago, and forgot.




So far so good. It’s easy enough to find evidence of animals eating things, giving you a link in a food chain. But just a few feet away was the next link. Here were the remains of a cottontail, no doubt one of those that had been feasting on elm bark, but caught by a predator and consumed on the spot.




What was the identity of the predator? The snow was clean enough all around the site that there clearly were no mammal tracks other than cottontail.




With some study it was possible to pick out bird marks.




Two tail marks, the first with associated primary feather grooves and indistinct impressions of feet. There seems to be some bearing down, and a hop forward with a second, deeper tail impression. The predator had killed the rabbit quickly, and kept it pinned with its feet while removing the head and feet, plucking out much of the fur, and apparently consuming all the rest except for a few bones.




Then the bird turned, and its departing two-footed push-off is plain. It leaped up so strongly that it did not leave the usual primary feather marks of the first wingbeat. The size and strength of this bird, as well as the dimensions of the tail impressions, say great horned owl to me. A hungry great horned seems capable of consuming a rabbit in one sitting, though it is conceivable that it carried part of its prey in its mouth when it departed. Do great horneds offer nuptial gifts? The nesting season is upon them.

Recent Raptor Notes

by Carl Strang


Here I want to offer a couple recent raptor observations at Mayslake Forest Preserve. First, around the turn of the year a female kestrel appeared in the eastern part of the preserve. She has been hunting frequently from a perch on the wires, looking down toward the abundant vole runs in the mowed fringe of St. Paschal Drive.




Driving past there on one of the coldest recent days, I saw her harassing a passing red-tail until it was away from her area.


Yesterday I mentioned that the burning brush piles had attracted someone’s attention other than mine. One of the larger fires had just built to a blaze when I noticed the pair of red-tails approaching from the southeast. They made a beeline for the smoke rising from the fire, and rode its tiny thermal (rising column of heated air) upward. Hawks are not regarded as particularly intelligent or playful birds, but this looked like play to me. Apparently this thermal was a disappointment, however, as each bird moved on after giving it a single try. Only then did I think of my camera. The best I can offer is the scene, with the smoke column evident, shortly after the red-tails left.



Brush Removal

by Carl Strang


One aspect of Mayslake Forest Preserve that struck me when I moved my office there in November was the impressive restoration work that was taking place (here I am talking about restoration of biological communities rather than the architectural restoration of the mansion, which also is an impressive ongoing process). I think of restoration as the removal of human influences that have disturbed ecological processes and are limiting biodiversity (the variety of life in a place).


The dedication of a group of volunteers deserves a major portion of the credit for this progress at Mayslake, and I will feature them in one or more future posts. For now I want to focus on recent support that their effort has received from Forest Preserve District staff.


A large part of restoration work is the removal of invasive plants that we have, deliberately or inadvertently, brought to our continent from other parts of the world. Liberated from the consumers and other limits that kept them in check in their native lands, these newcomers have an unfair advantage in their competition with North American plants. So, the task of people doing restoration is to serve as herbivores, evening the playing field by removing some of the invasives.


Earlier in January, a crew came in with a brush chomping machine and cleared out an area of buckthorn and honeysuckle that had filled the space beneath the oak trees between Mays Lake and the friary in the southeast corner of the preserve.




I was excited to see this, because it was clear that with those impressive trees in place, the invasive shrubs had been the major obstacle preventing that slope from becoming as beautiful as the previously restored savanna I have shown in past posts.




Then a crew came to burn the scattered brush piles the volunteers had accumulated over the past year in their painstaking hand-cutting of shrubs in woodlands elsewhere in the preserve. Wholesale clearing can’t be done in places where slopes are too steep or where the proportion of native plants is high. There, hand cutting is necessary. The brush pile fires and the smell of their smoke provided a welcome punctuation of my lunchtime walks through the preserve on those days.




I wasn’t the only one noticing those fires, as I will explain tomorrow.

Rookery Trees

by Carl Strang


The great blue heron was the bird that first inspired my interest in learning about nature when I was a 7-year-old, watching several of them in a small lake one calm summer evening. A few years later a number of great blue herons established a new nesting colony near my hometown of Culver, Indiana, among the large branches of a grove of sycamore trees  in a swampy woodland.




An interesting development over the past decade has been the proliferation of great blue heron rookeries in DuPage County. One on Danada Forest Preserve near the center of the county had 25 nests or so by 2001. Another large colony has been growing for several years at Pratts Wayne Woods. Close to there, at James Pate Phillips (Tri-County) State Park, an offshoot of the Pratts Wayne rookery existed for a few years in a group of dead trees, but this experiment is on the verge of ending as the trees lose branches. There is another small rookery at Churchill Forest Preserve, and a final one strung out along the Des Plaines River in and adjacent to southeast DuPage County.


Remembering the Indiana rookery, I was curious about what species of trees were supporting the Danada colony. On a recent frigid weekend morning I went there to find out. It had to be done in mid-winter, both to avoid disturbing the birds (which could begin to return by the end of February), and to take advantage of frozen ground and water for easy travel.




I found the colony to be situated in swampy woodland surrounding a large pond. Most of the 15-20 nest trees were living cottonwoods, and 90% of the nests were in these.




Two of the nest trees were dead, and three were willows. One cottonwood had 16 nests, a couple had 13, and one had 11.




I counted a total of 142 nests. There may have been more; we have had some strong wind storms since the nesting season which could have dismantled some nests. Like sycamores, cottonwoods have open canopies and thick branches capable of supporting the relatively large stick nests herons construct. Most of the trees in the colony woods were cottonwoods, so a statistical examination limited to that bit of woodland would not reveal much about heron preferences. It appeared likely that the other trees there simply lacked the necessary support structure. A few willows were used, but each had the capacity for fewer nests. The better question is how the birds choose the rookery site in the first place. Trying to answer that would require a longer-term examination of many colonies.

Geese? What Geese?

by Carl Strang


In recent days we have experienced a period of extreme winter weather that happens perhaps once in a decade. Temperatures dropped below 0ºF for a couple of days, reaching -20°F overnight. Snow depths approach a foot on the ground in most places (as my front yard attests).




As temperatures moderated to something approaching seasonal, I went out to check the county’s four largest winter goose roosts. Three of them were frozen, and the geese were gone: Blackwell, McDowell and Fullersburg.


Blackwell roost, frozen

Blackwell roost, frozen


All three are on expanded areas of streams above dams. It is likely that the relatively calm waters froze quickly after the geese had left for the day to feed, and they returned to find their roosting areas closed.


McDowell roost, frozen

McDowell roost, frozen


The fourth roost, at Hidden Lake on the East Branch of the DuPage River, remains open. Numbers do not appear to have been augmented significantly by transfers from the other roosts, holding steady at about 900 birds.


Hidden Lake roost January 19

Hidden Lake roost January 19


These remaining geese continue to find small areas where the snow is shallow enough that they can graze the lawns. Such areas are limited, however, and so the birds that departed had a double motivation. It seems likely they shifted south to a place where the snow is not so deep and roosting waters remain open. Older Canada geese are capable of remembering places to go in such extreme circumstances, and younger birds that follow them will learn the route and landmarks. I picked an extraordinary winter in which to begin this study. I look forward both to seeing whether the flocks return when the roosts open up again, and to seeing what they do in less extreme future winters.

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