St. James Farm Autumn Update

by Carl Strang

This blog has been on hiatus while I work on my annual research summary documents, but I have been paying regular visits to St. James Farm Forest Preserve, the site I monitor and where I soon will begin as volunteer steward. Today’s entry shares some photos from recent weeks.

Winged euonymus adds color to the autumn scene, but is an invasive shrub that will need to be removed at some point.

Winged euonymus adds color to the autumn scene, but is an invasive shrub that will need to be removed at some point.

As leaves come off the trees, bird nests are revealed. This oriole nest had a significant content of synthetic fibers, including fishing line from the nearby ponds. The fuzzy white object hanging below the nest is a fishing lure, the hook not quite visible at this angle.

As leaves come off the trees, bird nests are revealed. This oriole nest had a significant content of synthetic fibers, including fishing line from the nearby ponds. The fuzzy white object hanging below the nest is a fishing lure, the hook not quite visible at this angle.

This silver-spotted skipper still was active on November 16.

This silver-spotted skipper still was active on November 16.

The opossum lay dead in the center of a trail, also on November 16. Cause of death was not evident.

The opossum lay dead in the center of a trail, also on November 16. Cause of death was not evident.

Late autumn migrants included this white-crowned sparrow youngster.

Late autumn migrants included this white-crowned sparrow youngster.

The most unusual stopover duck was a female pintail on the east pond.

The most unusual stopover duck was a female pintail on the east pond.

Another duck worth noting was this male. Accompanied by a female mallard, his huge size and her identity suggest that he may be a mallard-black duck hybrid.

Another duck worth noting was this male. Accompanied by a female mallard, his huge size and her identity suggest that he may be a mallard-black duck hybrid.


First Snow

by Carl Strang

Our first winter storm of the season was worthy of the name, with 24 hours of occasionally heavy snowfall and strong winds. Even after some of the first snow melted in contact with the ground, St. James Farm Forest Preserve ended up with 3-6 inches on the ground. On Sunday I took an extended walk through the northern, forested portion of the preserve.

I wasn’t alone. Many hikers, skiers and snowshoers took advantage of the fresh snow.

I wasn’t alone. Many hikers, skiers and snowshoers took advantage of the fresh snow.

The wet snow stuck to the vegetation.

The wet snow stuck to the vegetation.

Herbaceous plants bowed under the weight.

Herbaceous plants bowed under the weight.

The smaller birds were challenged to find food through this obstruction. The temperature was cold enough to freeze shallow ponds.

This pond is hidden in the northwest corner of the woods.

This pond is hidden in the northwest corner of the woods.

This was my first opportunity to get an overview of mammal activity across the preserve. The absence of cottontail tracks perhaps was the biggest surprise. The more open southern part of the preserve, which I did not check, is more suited to them.

I saw only one set of opossum tracks, but would not expect much activity from them under the conditions.

I saw only one set of opossum tracks, but would not expect much activity from them under the conditions.

White-footed mice are abundant in the forest.

White-footed mice are abundant in the forest.

Coyote tracks showed a thorough coverage of the area overnight.

This footprint was made soon after the main snowfall ended. Ice crystals formed within it afterward.

This footprint was made soon after the main snowfall ended. Ice crystals formed within it afterward.

A pair of coyotes hunted together for a time.

A pair of coyotes hunted together for a time.

Though the disruption of the rut makes any pattern temporary, I was interested in assessing deer activity as well.

A few individuals crossed Winfield Road between St. James Farm and Blackwell Forest Preserves.

A few individuals crossed Winfield Road between St. James Farm and Blackwell Forest Preserves.

Half a dozen deer moved together at one point. The main activity was in the western portion of the woods, with almost all movement trending east-west. Only a couple deer, moving north-south, left tracks in the eastern portion. All of this is subject to change when things settle into the winter pattern over the next month.


Skunk at Mid-day

by Carl Strang

Twice in November, when my noontime walk has taken me into the former friary site at Mayslake Forest Preserve, I have seen a striped skunk out and about. The first time it was close to a known den hole, and the sighting was a novelty. Occasionally I have encountered other nocturnal mammals, including raccoons and opossums, out in the middle of the day over the years, and though I had not seen a skunk doing so, it’s also true that skunks are less common than those other animals. But then I saw the skunk the second time.

At first the skunk looked normal enough.

It was moving in the usual gait at the usual speed, apparently stopping frequently to pause, dig a little, apparently eat an insect, and continue. But then at one point it stopped and lifted its head, turning it in various directions and sniffing. The eyes looked strange.

Was it simply squinting in the unaccustomed light?

Another possibility is that the animal is blind. This likewise would not be unprecedented. When I worked at the Forest Preserve District of DuPage County’s Willowbrook Wildlife Center, I knew of several opossums that had been brought into the clinic over the years, opossums that had been congenitally blind. They were healthy otherwise, and had functioned well enough to achieve adulthood, but had wandered into places where they got into trouble. They could not be released, however, into an unfamiliar area, and so were kept on as exhibit animals.

Skunks, likewise nocturnal, also live largely by their noses. If this one is blind indeed, it seems to be staying in a part of the preserve where it will be able to maintain itself without negative encounters with dogs or people. There is no point in trying to trap it and take it to Willowbrook. The Wildlife Center’s permit from the state requires its staff to euthanize any skunks or bats that come in, because they are the animals most likely to have rabies. I will be interested in following this skunk’s career. After all, it may not be blind at all, just odd.

Raccoon Species Dossier

by Carl Strang

I am overdue to share one of my mammal dossiers. This one is relatively large. As always, the dossier is limited to my own experience. I established it in the mid-1980’s, and since have added dated notes.


Raccoon, Aransas NWR picnic area, Texas

Raccoons occur in a fairly wide range of habitats, though they usually live in areas with some trees and wetlands. They can be abundant in residential areas. Raccoons are nocturnal, spending the day in a hollow tree or a woodchuck burrow (alternatively, in shed, attic, or chimney). They are active all year round, though somewhat less so in winter. They avoid activity in storms or extremely cold temperatures. Sometimes they sun themselves on a branch in summer. Centers of foraging activity are garbage cans in residential areas, and ponds, streams or marshes elsewhere. Their diet is extremely broad, but features small aquatic invertebrates and vertebrates (crayfish especially favored), also fruits and insects from terrestrial areas.

Females have 1 litter of young per year, born mostly in April or early May in northeast Illinois. Young remain in the nest several weeks, then begin following the mother (father doesn’t participate in rearing). Separation begins around September. Young often remain together in 2’s or more through their first winter. The young are especially vocal, uttering a rolling chatter when interacting with one another, giving loud cries when picked up, and occasionally giving a distinctive rising whimper which may be a call for mother. In play, young bounce around with shoulders humped above stiff front legs and hair raised. This probably leads into an aggressive display of adulthood.

21DE86. A well-established trail leads from a bur oak den tree for 20m, then splits 3 ways into fainter paths. All sets of tracks visible on that trunk led away from the den tree.

Raccoons, creatures of habit with a heavy walk on flat feet, produce clear trails in winter.

15JA87. Raccoon tracks in Willowbrook Back 40 are the first sign of that species I have seen on several preserves since heavy snow fell almost a week ago. This one seemed to be trying to minimize contact with the snow by walking on logs, walking on melted patches, and bounding in open stretches where deeper snow couldn’t be avoided.

20JA87. No raccoon signs in 3 days since new snow.

9FE87. Raccoon were active in the center of the Willowbrook Back 40 last night.

3JE87. A raccoon gnawed on a rabbit hind foot in brush near the great horned owl nest, Willowbrook Forest Preserve, at mid-day. It ran off quietly as I passed, at a fast diagonal walk or a trot.

22AU87. Photo and sketch of raccoon gallop, lope. 15 inches up to next set, 16.5 inches back to previous set, which was 14 x 5.5″ and looked a little more gallop-like. The set before that (19 inches back) was a gallop, borderline bound.

Sketch of raccoon gallop

Sketch of raccoon lope

14NO87. A raccoon was dying of distemper at Winfield Mounds Forest Preserve. It was on its back, eyes crusted shut.

Canine distemper is one of the most important causes of death in northeast Illinois raccoons.

10DE87. Lots of fresh raccoon tracks are all over Willowbrook Back 40 trails, compared to only 1 fresh set of opossum tracks.

23DE87. There has been some raccoon activity in recent nights, and much opossum activity.

16JA88. Considerable raccoon action last night, which was warm. No opossum tracks.

20JA88. Lots of raccoon and opossum activity last 2 warm nights, Willowbrook. The stream was high, no crossings observed.

The flat-footed, 5-fingered raccoon footprint is distinctive.

17MY88. A raccoon was resting, perhaps sleeping, on an exposed horizontal branch near the top of a big willow, at midday.

12OC88. A raccoon was out at midday, Willowbrook Back 40 (I made several daytime observations of this animal in the rest of this month).

19DE88. 2 raccoons but no opossums were active the last 2 nights around the Back 40 Nature Trail.

Raccoons normally walk in the pace gait.

9MR89. Despite increased warmth over past 2 nights, there has been no use of trails by raccoons.

2AP89. Photos of 2 raccoons asleep in the 29-inch pin oak near the NE corner of Cactus Camp, near Hartz Lake, in Indiana. I saw the one in the hole first, didn’t see the other (in the crotch of a fork just above hole) until I looked with binoculars.

The raccoons described on April 2, 1989. These probably were siblings from the previous year, not yet breeding.

13MY89. 2 raccoons in the same sleeping places as on 2AP.

10JE90. Warrenville Grove Forest Preserve. A raccoon was active in the woods not far from the river (though at least 30 yards from it), half an hour after sunrise, foraging among Solomon’s plume in the forest. When I, standing still 15 yards away, shifted, it jumped onto a tree trunk, but I kept still in my camo sweatshirt and the raccoon resumed its foraging. Later I looked at the area. The vegetation was stepped on and disrupted, with common 2-3-inch holes, scrapes.

26JA92. Hidden Lake Forest Preserve. Raccoons were active last night (fresh snow yesterday, overnight low around 20F). I found a raccoon inside a hollow oak, at ground level, sheltered by the overhang of the leaning trunk. It looked back at me, but did nothing more.

JE99. Tracks seen at Horsethief Canyon, central Kansas.

19JA99. Willowbrook. Raccoons came out for the first time since the major snowstorm of 2JA, sometime between the 15th and today.

26JA00. In spite of the very cold previous night (subzero F), raccoons were out, at least 2 individuals moving together. This winter a group of raccoons is moving back and forth between a den high up in a dead willow near the Willowbrook bridge, and a den along the nature trail in a smaller dying willow. On the coldest nights they tend not to use the bridge willow den, which is higher up and has a larger hole which goes practically down to the bottom of the den. The trail willow den has a smaller hole, is not so exposed, and at least one animal can fit below the bottom edge of the hole. On the warmer nights, though, they seem to prefer the more spacious bridge willow den.

Raccoon skeleton. Raccoon and deer bones are the ones most frequently encountered in the field.

31JA00. A raccoon was out last night in the newly added 6 inches of snow, gait in the deep snow entirely a diagonal walk for a long distance.

4MR00. Hemlock Hill, Morton Arboretum. After a night that dropped into the 20’s, a raccoon slept in the open crotch of a large red oak, 10 feet off the ground. Now sunny, 30’s.

1AP00. While running on the Prairie Path between Butterfield and Kirk Roads, I spotted a raccoon sleeping on a large, open branch of an oak in a small wooded area beside the trail. A warm, sunny day.

30AP00. Raccoon snoozing in a dead tree trunk, largely hidden in a rotted out cavity 12 feet up and only about 20 feet from the busy main trail at Waterfall Glen (section parallel to S railroad tracks).

The raccoon skull is distinctive in its size, rounded form, and mix of canine and flattened molar teeth.

9AU00. Last night at 3am, loud cries eventually got me out of a deep sleep. Going to the window I saw a raccoon below, uttering the last of the cries. They were loud, and different from other raccoon vocalizations I have heard. The sound was sniffing or snorting, even whinnying in quality but very high pitched and sounding like a conflict or fear-driven vocalization.

28DE00. At 1:30 p.m., a raccoon was eating snow from the large upper limbs of the big, largely dead tree 40‑50 yards NNE of the Willowbrook office building (visible from the north office window). It then turned around and climbed down into the large crack on the SE corner of the trunk. This marks the 4th confirmed den on the preserve, and the 3rd winter den (the hollow catalpa behind the opossum cage in the outdoor animal exhibit is known only to have been used by a female to keep her tiny cubs in spring of this year). The deep snow that fell in mid-December has kept raccoons in their dens for more than 2 weeks.

Raccoons create communal toilets, often on elevated tree branches. This one, at the base of several joined tree trunks, shows a heavy recent diet of mulberries by the local raccoons.

13JA01. At 10:30 a.m., a large raccoon was walking a deer trail near the place where the regional trail crosses the back marsh at Herrick Lake. It seemed perfectly healthy. After a short time it left the deer trail and, with some effort, forged its own path through the still-deep snow.

26AP01. Sounds of baby raccoons coming from the same catalpa as last year at Willowbrook. (Last year she moved the 2 young to another tree when they were old enough to walk; this one has a very small entrance).

Older youngsters peek out from their den.

19MY01. A large raccoon was well exposed on the open branches of a dying oak at the Arboretum, grooming itself at 9 a.m.

21MR02. A raccoon shifted into a diagonal walk on a wet-snow hillside. Better traction? No overlap-separation between the tracks of each side. Elsewhere in flat areas, it used the pace gait.

14AP02. A female raccoon carrying a baby smaller than her head, more than 250 yards along the edge of the east side of Lake Maxinkuckee (Indiana), between 2:30 and 3:00 p.m.

2012. My notes since 2002 have been logged mainly in my natural history survey records at Willowbrook, Fullersburg and Mayslake. At Willowbrook it seemed that every year a female had her litter in a smaller den (warmer? more secure from males?), and at some point shifted them to a larger more open one. At Fullersburg I was impressed by the raccoons’ willingness to go out on very cold nights that elsewhere usually would keep them in. Even on single digit (F) nights, they routinely swam across Salt Creek rather than going the long way and taking a bridge. I started this blog at the same time my office shifted to Mayslake, and any significant observations from November 2008 on could be found by searching on “raccoon.”

West Bluffs Walk: 1

by Carl Strang

Once or twice a winter I like to get into the south part of Waterfall Glen Forest Preserve. Apart from the general attraction of being our most biologically and topographically diverse area, and scenically beautiful, it also is where a bobcat is most likely to show up. I didn’t find any bobcat signs this time, but the warm (40F) conditions made for some interesting tracking.

Footprints were deteriorating rapidly. Here is a comparison of one of my tracks going in against a fresh one as I came out less than 3 hours later.

Most trails were composed of blob tracks.

A typical coyote trail that day.

When I found sharply defined footprints, I knew they had to be fresh.

This coyote trail couldn’t be more than half an hour old.

Another fresh coyote track on deeper snow.

Blob tracking does allow some species identification.

Small round footprints in a diagonal walk, within half a mile of a residential neighborhood, point to domestic cat.

Sheltered from the sun and close to the base of a tree, the next trail had held up better.

The odd, irregular footprints of an opossum.

It wasn’t all tracks, though. Away from the trails I encountered several deer.

This young buck allowed a relatively close approach.

A track of a different sort was this old concrete and rock structure. I don’t remember encountering it before.

It appears to be one of the old Lincoln Park Nursery cribs, but it is away from the main trail, and distant from the others.

I also got some winter plant photos, which I’ll share next time.

Prehistoric Life 19

by Carl Strang

This year’s winter series has been a review of the prehistoric life and geologic history of northeast Illinois. Each chapter has summarized current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert. Today’s chapter concludes the series.

At last we reach the most recent times. This mastodon and its kind lived in our area in the recent past.

Pleistocene Epoch (1.64 million years ago to the present day)

The Pleistocene Epoch (named 1839), literally “most recent,” marks the latest series of continental glacial times. We are in an interglacial interval, regarded as part of the Pleistocene by some, by others named separately the Holocene (1885) or Recent (1833) Epoch.

Life on Earth. This is the time when our human species Homo sapiens evolved, along with the rest of the modern species. Our species originated in Africa around 200,000 years ago as it separated from its earlier hominid precursors, then began to migrate out of Africa around 100,000 years ago, fanning out into Europe, Asia, Polynesia-Australia and ultimately North America. Homo erectus earlier (1.5 million to 770,000 years ago) ranged from Kenya to China (Science 323:1197, 1419). Shaped tools and red ochre use suggest modern-like behavior had begun to appear by 164,000 years ago (Science 318:777). Genetic studies indicate that the Neandertals were a separate species, though they shared with us a gene for speech communication (Science 318:546). Skin color may have diversified in our species much more recently, with pale skins in some races developing only within the past 5300-12,000 years (Science 316:364).

Reconstructed giant ground sloth, Mastodon State Historic Site, Missouri.

There were new arrivals in North America from South America: 2 sloth genera (Nothrotheriops and Eremotherium), opossum, anteaters. And, from Eurasia, mammoths, bison, saiga, musk oxen, and humans. The polar bear evolved away from brown bear ancestors of the southeast Alaska area around 150,000 years ago. Many large birds and mammals became extinct, in many areas (including North America) because of human hunting (Science 300:885; 306:70).

Local landscape. This was a time of ice ages, more than 20 periods of continental glaciation alternating with periods when the glaciers retreated (only 4 of these reached as far as the Mississippi River drainage basin). The dominant theory ties the growth and ebbing of glaciers to regular cycles in the Earth’s orbit, tilt, and precession. Up until 1 million years ago, the glacial cycles were 41,000 years long, corresponding to the cycling of the Earth’s tilt. For the past million years the cycle has become 100,000 years long, for reasons that are unexplained but may be connected to a change in atmospheric carbon dioxide.

Rotten or weathered rock had formed at the surface; most of this was removed by Pleistocene glaciers. Glaciers don’t remove much thickness of bedrock, however, carrying mostly fractured pieces. In the DuPage County area, the glaciers scoured the Silurian dolomite bedrock clean of any sediments, except for the Devonian or Mississippian marine clays in cracks on the upper surface (this is why there are no pre-Pleistocene terrestrial fossils in much of northeast Illinois).

If we could clear the glacial deposits from our bedrock we might see something like this, grooves scratched on the surface by the glacier as it pushed southwest out of the Lake Michigan basin. Rock Point, Ontario.

Dolomite bedrock escarpments such as the one tracing the western and southern boundary of the Lake Michigan basin, and other highlands such as the northern Wisconsin Arch, played a significant role in channeling glacial flow. Lake Michigan started as a south-flowing stream. The sequence and timing of events: the Nebraskan glacial advance 1.8mya (million years ago), then the Aftonian interglacial stage, then the Kansan advance 900-600kya (thousand years ago), then the Yarmouthian interglacial, then the Illinoian advance 400-300kya, then the Sangamon interglacial, then the Wisconsinan glacial advance began 100kya and ended 18kya. Within the Wisconsinan there was an Altonian advance 70-30kya that reached northeast Illinois, a retreat 30-22kya called Farmdalian time, and the largest final advance 22-18kya called the Woodfordian.

A continental glacier was not a single body, but rather several rivers of ice, or lobes, flowing side by side. The Silurian escarpment divided the Lake Michigan lobe from the Green Bay lobe. Kettle Moraine in Wisconsin is a glacial deposit left between those lobes. The Lake Michigan Lobe had to climb (be pushed) several hundred feet to overtop the escarpment and enter northeast Illinois.

As the glacier advanced, the Straits of Mackinac outlet became blocked, and Lake Michigan drained south through the Chicago and Des Plaines Rivers. The Glenwood phase of Glacial Lake Chicago, as it is called, was followed by alternating advances and retreats that blocked and opened the Mackinac Straits and further eroded the Des Plaines valley. Because the weight of the glacier had depressed the crust, for a time after the last glacial retreat the river through the Straits lowered Lake Michigan (in that incarnation called Lake Chippewa) to the point where it was much smaller and occupied only part of its current area. Crustal rebound later raised the northern end of the lake to the point where the current basin filled. When the Upper Peninsula of Michigan, Lake Huron and part of Lake Superior were cleared of retreating glacial ice but other outlets still were blocked, the Des Plaines became the major drainage for all three lakes.

In 2007-2008 Mastodon Camp, a partnership between the Forest Preserve District of DuPage County and the Field Museum of Natural History, gave high school teachers and students an opportunity to participate in a dig. Bits of mastodon bone and tusk, as well as buried black spruce trees and cones, were the main physical product from the site at Pratts Wayne Woods Forest Preserve.

During the latest, Wisconsin glaciation, the permafrost (tundra) zone was 50-120 miles wide beyond the glacial margin, and the mean annual temperature was about 5 degrees C cooler than today. Most of our familiar prairie and forest species were restricted to rather small refuges in the South during the glacial maximum, though oaks and hickories occupied a large part of the southern U.S. Species occurred in unfamiliar combinations, which changed as environmental conditions shifted (i.e., distributed themselves according to individual species tolerances rather than in community clusters of species).

According to recent work with cores from Nelson Lake in Kane County and Brewster Creek in DuPage, our landscape originated 18,000 years ago as the Wisconsin glacier melted away. By 17,000 years ago the glacier locally had shrunk back to the Lake Michigan basin. Open sedge tundra with some spruce trees invaded the zone nearest the glacier (18,000-16,000 years ago), then white spruces filled in to form a recognizable northern coniferous forest until around 15,000 years ago. The climate was dry and windy, piling a layer of loess (silty material) on top of the glacial till and outwash. The wind diminished and the climate became wet around 15,000 years ago because of the collision of warm air from the Gulf with polar air from the glacier north of us. White spruce declined, with black spruce becoming important in low wet areas, and black ash and fir along with a variety of deciduous trees invading the uplands. The glacier retreated to Canada by 13,000 years ago, then advanced in a new cool period as far as northern Wisconsin and the U.P. of Michigan (this may have been a Northern-Hemisphere-only cooling: Science 318:86), and began its final retreat 11,650 years ago. Then alder, birch, jack pine, ironwoods and elms increased locally, and additional trees invaded until a mix of deciduous species, including lots of oaks, was achieved. Beginning around 10,000 years ago there was a drying period, which led to the spread of prairie through our area. The prairie then retreated a little, so that by 6200 years ago our area became a prairie with islands of woodlands.

Local life. After the Wisconsin glacier retreated, first there was tundra, home of woolly mammoths (grazers), musk oxen, caribou, collared lemmings and other animals now extinct or found only in arctic Canada and Alaska. People arrived at this time, hunting with spears (one of the earliest human sites in North America, with butchered mammoth bones dated at 12,500 years ago, has been discovered just north of here near Kenosha; Science 305:590). As the forest filled in the warming landscape, additional mammals included moose, stag moose, scimitar cats, dire wolves, giant beavers, snowshoe hares, Jefferson’s ground sloths and mastodons (unlike mammoths these were browsers which also ate walnuts, spruce cones and other seeds; some species such as Kentucky coffee tree and osage orange are thought to be relatively uncommon today because they have lost mastodons and other large herbivores as seed dispersers). During the time of deciduous forest, local mammals included mountain lion, bobcat, red wolf, elk, white-tailed deer, raccoon, gray fox, porcupine, black bear, flying squirrel and gray squirrel. The prairie and mixed prairie savanna of historical times included today’s familiar animals, along with black bears, badgers, mountain lions, red wolves, elk and bison.

Imagined Paleoindians, Mastodon State Historic Site, Missouri.

Clovis points have been found in DuPage County, indicating that some of those early big animal hunters (known as Paleoindians) were here. The largest animals became extinct, thanks in large part to the Paleoindians’ killing them faster than they could reproduce (Science 326: 1100). Subsequent human cultures wandered less, and shifted to more of a hunting-gathering economy in the several thousands of years of the Archaic Period. Thrust spears and spear-throwers did not give way to bow and arrow in North America until later, during the Woodland Period that began with early signs of agriculture about 2000 years ago. Agriculture did not become an important part of the local economy until the most recent 1500-1000 years. The Woodland people were even more sedentary than Archaic people, and used pottery. Mississippian and Oneota cultural influences, centered in west central Illinois and Wisconsin, respectively, were characterized by increasing social-political complexity made possible by corn-based agriculture. Ultimately the familiar tribes emerged, in northeastern Illinois the Miami followed by the Potawatomi.

For a time in recent years, a group of researchers attempted to make the case that a comet or other extraterrestrial object exploded over North America, causing a climatic cooling (the Younger Dryas time), ending the Clovis culture and resulting in the extinction of the North American megafauna. By the end of 2010 a number of studies had invalidated the supposed evidence for this idea and shown that the Younger Dryas was the result of a sudden influx of cold, fresh glacial meltwater into the northern oceans that for a time shut down the Gulf Stream current.

Prehistoric Life 18

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Pliocene Epoch (5.2-1.64 million years ago)

The Pliocene Epoch, literally “more recent,” originally was defined (1833) by the percentage of then known fossil mollusk species still living (35-95%). Its end is marked by the beginning of the glacial times.

Life on Earth. In the Pliocene, grazers became largely supplanted by more generalist herbivores as savannas became widespread in Eurasia and North America. The dominant groups were camels, antilocaprids (e.g., pronghorn “antelope”), and Equus horses (which, like most horses, originated in North America). Opossums diversified in South America, mammoths appeared in Africa (early Pliocene), the North American rhinoceroses vanished (middle Pliocene), and Sorex shrews appeared in the late Pliocene.

Sorex shrews like our short-tailed shrew of today made their evolutionary appearance in the Pliocene Epoch.

Land bridges finally allowed camels to spread into South America and Asia in the Pliocene (a camel survived in North America into late Pleistocene times). In the middle Pliocene, continued connection to Asia brought immigration of more carnivores, deer, and the elephant Stegomastodon. From North America to Eurasia went a rabbit, a squirrel, the beaver, and Equus.

The world’s lynx and cheetahs first appeared in North America, crossing to the Old World via the Bering Sea land connection.

In the late Pliocene, new appearances were pocket gophers, the white-tailed deer genus Odocoileus, raccoons, the giant beaver, bobcat (Old World lynxes, and also cheetahs, trace their ancestry to the New World where their groups first appeared), the New World porcupine family, eastern mole, and masked shrew.

Modern deer made their appearance in the Pliocene.

In the meantime, the first hominids were beginning to walk upright in Africa 3.8-4 mya (million years ago; Science 307:1545). Upright walking may have begun in the trees, as a hand-assisted way of negotiating thin, flexible branches (Science 316:1328 ). “Lucy,” Australopithecus afarensis (3-3.6my ago), regarded as a human ancestor or close to it, has been tied to the older A. anamensis (4mya), which in turn may have come from the still older Ardipithecus ramidus (4.4mya). Fossils of all three species were found in the same African river valley (Science 312:178). Ardipithecus significantly was a woodland dweller; apparently upright walking was not a product of a grassland habitat (Science 326: 64). Genus Homo had evolved by the late Pliocene, with species from Africa to Asia. Homo habilis and H. erectus are two earlier species which apparently overlapped considerably in time, so that it is uncertain whether the latter descended from the former (Science 317:733). Examination of limb structure points to habilis being arboreal while erectus was terrestrial, so a connection by descent is unlikely (Science 320:609).

The New World chickadees evolved from a single species that emigrated from Eurasia in the Pliocene.

Birds also were dispersing, and our modern species began to emerge. At least some modern songbirds had evolved by the early Pliocene (Auk 124:85). The chickadees and titmice, which had appeared in Eurasia originally, came over to North America in the Pliocene. The first crested species (titmouse) came over around 4 mya, and a single non-crested (chickadee) founder species around 3.5 mya. Subsequent evolution led to the 3 modern titmouse species and about 7 chickadees in the Americas. One terror bird species, in genus Titanis, reached North America from South America 2-3 million years ago, but was extinct by the end of the Pliocene.

Local landscape. Cooling and increased seasonality continued in the Pliocene (the middle Pliocene was the last time that Earth temperatures were warmer than at present).  Climate in the early Pliocene was significantly warmer than today; the major difference apparently was that the El Niño pattern of Pacific Ocean currents was permanent rather than episodic as it is today. The re-establishment of such a pattern is a possible outcome of global warming (Science 312:1485). Woodlands were more open in the Pliocene, perhaps savanna-like in places in our area. Elsewhere in North America, the continent developed its first near-modern boreal forest, as well as the first deserts, tundra and permafrost areas.

The Pliocene brought increasing seasonality, and extensive savannas replaced much of the Miocene grasslands.

The nearest Pliocene deposits are tiny areas in southern Indiana, and extensive areas in eastern Nebraska. By the Pliocene, much of northeast Illinois was draining eastward into the river that ultimately was enlarged by Pleistocene glaciation to become Lake Michigan. This happened when the relatively erosion-resistant and eastward-sloping Niagaran dolomite beneath us was brought close to the surface. Today, surface waters are directed by much more recent glacial deposits on top of that bedrock, and all ultimately flow into the Des Plaines-Illinois River system, ending up in the Gulf of Mexico rather than the North Atlantic.

Local life.  There is a likelihood that the camels, antilocaprids and horses (including Equus, the genus that includes modern horses) were represented locally. Deer, rabbits, beavers, raccoons, sabertooth cats (including Meganteron, an ancestor of the famous Smilodon), bears, the scavenging “hyaenoid dog” Borophagus, otters, and skunks are other likely species at that time.

Prehistoric Life 17

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Neogene Period (23.3 million years ago-present), Miocene Epoch (23.3-5.2 million years ago)

The Neogene Period (named in 1853) defines a time when a significant portion of fossil species (or at least very close relatives of them) still are in existence. The Miocene Epoch (established 1833), literally “few recent,” originally was defined by the percentage of then known fossil mollusk species still living (17%).

Life on Earth. Warming but continued dry conditions prevailed through most of the Miocene, giving way to renewed cooling in the late Miocene. This cooling was caused at least in part by the continuing growth of the Antarctic ice sheet. The resultant drop in sea level established land bridge connections from North America to South America and Asia. Continental growth, and also the rise of major mountain ranges, increased the seasonality of climate, and changed ocean circulation patterns, with upwelling zones probably setting up the conditions favoring pinniped (sea lion, etc.) evolution in the middle Miocene.

Harbor seal. Pinnipeds underwent a significant radiation in the Miocene.

Grasslands spread in the Miocene. The Perissodactyla had been the dominant ungulates, with their diversity peaking in the Eocene, but in the Miocene they declined (though rhinoceroses remained prominent throughout the epoch), while the Artiodactyla increased. The latter ungulates’ advantage may have been their ruminant digestive tract and complex high-crowned teeth, good for grazers (this was true of the larger division of artiodactyls; the pigs and hippopotami lack these specializations). Camels were very diverse in the Miocene, a remarkable example being the 12-foot-tall, giraffe-like browser Aepycamelus.

Bactrian camels, Brookfield Zoo. The camels, which had their start in North America, were very diverse on our continent in the Miocene.

The deer family appeared early in the Miocene in the Old World. By the middle Miocene, the diversification and evolution of horses was represented in part by the first one-toed species, Pliohippus of North America. Horses did not develop high-crowned molars until 4 million years after the grasses replaced trees as the dominant vegetation in the Great Plains, but their limb structure changed more quickly, so that they were able to survive by efficiently traveling longer distances between suitable habitat patches (Science 306:1467). Ungulate diversity peaked in the mid-Miocene, perhaps because frequent disturbance by the large proboscideans (gomphotheres and mastodons, which migrated into North America at that time) diversified the grassland savanna that had developed. Toward the end of the Miocene, however, much of the savanna gave way to grasslands, and there were extinctions of many of these ungulates and proboscideans.

Prairies and other grassland ecosystems spread into North America and became important here in the Miocene.

The departure of forests from much of North America is associated with the vanishing of primates from this continent.  Miocene land connections to South America and Asia resulted in significant immigrations and extinctions. Sabertooth cats and other Felidae first immigrated from Asia in the middle Miocene (ending the so-called “cat gap”).  Other new Miocene arrivals from Asia included bears, skunks, and badgers; from South America, ground sloths. There was a diversification of canids (dog family), mustelids (weasel family) and amphicyonids, though in the late Miocene the amphicyonids became extinct. The American white-footed mouse genus Peromyscus first appeared in the Miocene, and Spermophilus ground squirrels in the middle Miocene. Flying squirrels had their start in Asia in the early Miocene, with the split between Old World and North American flying squirrels happening in the late Miocene. The dominant carnivores in South America were marsupials in the Tertiary through the Miocene. The first member of the opossum genus, Didelphis solimoensis, showed up in the fossil record of Brazil in the latter part of the Miocene. Marsupials went extinct in North America in the Miocene, however.

Bears evolved in the Old World, and crossed the Bering Sea land bridge into North America in the Miocene.

Modern bird families were established in the Miocene, and the land bird orders other than the passerines underwent their great diversification. The passerine (perching birds) explosion began in the late Miocene. The first modern genera of birds began to appear in the Miocene, as well.

Local landscape. Subtropical forest of the early Miocene gave way to warm temperate to cooler temperate forests. The Texas gulf coast was swampy, so our climate very likely was at least as moist as today. We were between known areas of forests in New England that were warm temperate (hickories, chestnuts, hollies, mulberries, gums, oaks, buckthorns, elms, grapes) and shrubland-savannas on the Plains (invaded by grasses and prairie forbs as the Miocene progressed). The closest Miocene deposits are in western Nebraska, south central South Dakota, central Mississippi and SW Maryland.

Local life. Throughout the Miocene, browser-grazer pairs of rhinoceroses were found all over North America in savanna environments (the most common genera were Aphelops and Teleoceras, respectively; Teleoceras appears to have been a herding, and possibly semiaquatic species). If our area was more forested, we may have had only a browsing species. Rhinos became extinct in North America at the end of the Miocene. It seems likely that our area witnessed the transition from perissodactyl to artiodactyl dominance. Forms of rhinos (5 genera), tapirs (2 genera), horses (14 genera), dromomerycids (an extinct group of deer-like woodland browsers with horned males) and camels (5 genera, including the giraffe-like Aepycamelus) probably were here. The oreodonts were a diverse group of pig-like herbivorous artiodactyls, with at least 4 genera probably here in the Miocene. Carnivora would have been the dominant predators (diverse dogs, weasels, the large bears Indarctos and Plionarctos, “bear-dogs,” large cats, and the saber-toothed nimravid Barbourofelis), but there was also the entelodont Dinohyus. The Miocene also saw the arrival of the first proboscideans, or elephant relatives. These may have had a significant impact, killing the trees that they fed on and thus disturbing the vegetation so as to create more habitat diversity. There likely were 3 genera here, including two that were relatively elephant-like, and one that had shovel-like lower tusks that it probably used both to scoop up aquatic plants and to scrape bark from trees.

Blob Tracking

by Carl Strang

The title for this entry is not a technical term. It simply refers to the interpretation of tracks that are blobs rather than well-defined footprints. The mix of rain and snow we experienced on Monday provided a good opportunity for this practice. Here’s an example from the south savanna at Mayslake Forest Preserve.

What do you make of these blobby footprints?

Here an opossum was walking, left to right in the photo. As usual, the oddly shaped hind foot with its enormous big toe is turned sideways. The more uniform toes of the front foot are widely spread. The left-hand pair of blobs were made by the right feet, the middle pair by the left feet, the right-hand pair by the right feet again. You can see clearer reference examples in my tracking primer here.

I was interested to see that a raccoon had circumnavigated May‘s Lake Monday night, with various side trips into different woodlands, up and down a few trees, etc.

Do you recognize these as raccoon tracks?

The blobs in this case are recognizable as raccoon tracks because of the side-by-side pairs of footprints, indicative of the raccoon’s distinctive pace gait. Their size and spacing are consistent with the raccoon’s body size. Raccoon activity was especially concentrated in the west end of the south savanna, not far from the former friary, and the footprints had merged into the distinctive trails formed by the big flat feet of raccoons when they travel a route frequently.

Raccoon trails are easy to see in winter.

I suspected the raccoon’s den must be in this area, and sure enough, the trail led to a concrete culvert that empties into May’s Lake.

The trail comes to the culvert from the left and enters along the left edge.

In contrast to the blobs that the raccoon made during most of its excursion, it left very clear tracks as it entered the culvert. The animal still was inside, as there were no exiting tracks.

If you look closely you may be able to see a few clear footprints on the trail.

The possibility is open that more than one raccoon is involved, and that the one in the culvert was different from the one that went around the lake. This may seem a strange choice for a den, but it’s secure, and probably dry enough this time of year. I wonder if this might be the raccoon that used to live in the friary. That animal, evicted by the demolition, had grown accustomed to denning in a human structure. The concrete culvert might seem a more comfortable new home than a hollow tree.

Today’s final example had me fooled at first. This animal was doing a lot of its travel with the bound gait, and my interest in the mink had me thinking I had found a mink’s trail.

These sets of four tracks are in a pattern typical of the bound gait.

Again, you can find a description and clear photo of a mink’s bound gait pattern at the post on gaits. Eventually I had to abandon my initial idea. These footprints were too small and narrow, the sets of tracks were too close together for such shallow snow, and this animal was spending a lot of time downshifted into a diagonal walk.

The animal in question was slowing to a diagonal walk gait whenever it entered taller vegetation.

It doesn’t happen that often in mid-January, but a skunk had come out and covered a lot of ground Monday night. The temperature was in the 20’s that night, the warmest of the month, so it was not so far out of the realm of possibility. Still, it merited an entry in my skunk dossier.

Opossum Dossier

by Carl Strang

I like our native marsupial, as the length and content of this week’s species dossier may reveal.


Common in DuPage County, IL, and around Culver, IN. Usually found around trees, though it more often uses burrows (dug by other animals) as daytime rest sites in DuPage. Strictly nocturnal most of year, but comes out for occasional daytime wanderings, especially in late winter. Has a prehensile tail. Female has pouch in which small young reside; older ones ride on her back. Highly variable in most physical characteristics, including facial appearance, color (black, white and gray offspring once in a single litter brought to Willowbrook). Breeding season varies, too; young babies with mother May-August. Climbs trees frequently. Tracks 5 toes front and back, usually walks in trot gait, with front foot’s toes spread widely, giving impression of a star. Hind foot of same side placed sideways, large thumb pointing inward, remaining 4 toes out, and placed against back of front foot so as to appear to be partly wrapped around it. Dead ones are so common along the road that auto accidents may be the major cause of death in DuPage. Opossums usually don’t snap or bite. They give an open-mouthed, hissing threat. Are the over-sized but weakly anchored canines more for bluffing than eating? Usually they can be carried by the tail, but this is not recommended because some will climb up and try to bite. I haven’t seen the “playing possum;” when this behavior is reported to Willowbrook, it’s usually in the context of the animal being bitten by a dog. The skull is characterized by a large cranial ridge and tiny brain cavity.

25JA86. Willowbrook. Heavy raccoon and opossum activity after snow fell but before a large, sharp drop in temperature.

18FE86. Tracks indicated much opossum (also skunk, raccoon) activity on a relatively warm night after a week of extreme cold and an ice storm.

10NO86. Young opossum making a nest in its aquarium at Willowbrook. Tore off pieces of newspaper from floor with mouth and carried them in tightly curled tail into folded towel, further shredding and incorporating them into previously gathered material. After initial tear, pushed paper with front feet underneath him, transferring or pushing it into partly curved tail with hind feet. Tail gripped paper. Hind feet appeared to grasp the material, even small pieces, and stretched the feet backwards to stuff them into the growing bundle.

11JA87. Waterfall Glen, in 6 inches of snow that fell 2 days before. No raccoon signs, but several opossums had been out (all from burrows in ground). One followed in young woods between railroad tracks and Des Plaines River, east of Sawmill Creek. It dug a hole and defecated skins and seeds of American bittersweet or something very similar at base of large tree. Went into and out of a second burrow distant from the first. Frequently and I believe nonrandomly brushed against large trees. Straddle wide (7.5 inches). Dug in 2 other places; couldn’t tell if it ate anything. Entire counterclockwise circular path ~300m long.

20JA87. No sign of opossums in the 3 nights since 4 inches of snow.

14MR87. Meacham Grove. Medium-sized opossum tracks on long, roundabout path through woods and on out of preserve. I picked up another, same size (same animal?), followed it to hollow-log den. Frequently turned to the side and dug shallowly in litter. Three times its path crossed similar thick (1/2-3/4″ diameter, ~2″ long segments) droppings med-dark brown with fibrous matrix and much seed content, looking like millet from bird feeder. I don’t think these were deposited by this animal on this trip, though. No frequent contact with trees, though the second animal seemed to prefer to walk along tops of fallen logs and sticks rather than walk on ground (1/2″ new icy snow on ground). Holes in litter mostly distinct from those dug by squirrels by being less focused, shallow scrapings. Typically wider than long, as opposed to squirrels’ longer than wide, and without nut-hole in bottom. Possibly a more circular, displacement of litter rather than the squirrels’ linear digging. I backtracked the original animal’s winding route until it went off the preserve on its north edge (entire ramble encompassed ~1/3 of the small western part of Meacham Grove). It dug out an old rabbit skin, fur still on, but apparently didn’t find anything edible left.

10DE87. One set fresh opossum tracks in Willowbrook’s Back 40, compared to lots of raccoon sets.

23DE87. In recent nights much opossum activity, some raccoon activity.

20JA88. Lots of raccoon and opossum activity last 2 warm nights, Willowbrook. Stream high, no crossings observed.

1JE88. An adult opossum out and quietly moving about at this hot noontime hour (>85 degrees F).

9MR89. Despite increased warmth over past 2 nights, no use of trails by opossums or raccoons.

9DE89. McDowell Forest Preserve. Half-grown opossum, foraging mid-morning. Nose very active, ate several small fruits among fallen leaves. Hackberries. It was unwary; I could approach closely. When walking it tends to trot, especially when it speeds up. 4 separate footfalls when slower, but they are departures from a diagonal walk or trot sequence rather than a pace. Later (11:30am) I saw him, or another of same size, go into a burrow about 1/4 mile away from the first site.

14JA90. Most of a roll of photos taken in the dried bed of McKee Marsh, of an opossum eating a dead fish, ~10:30am.

22JA90. Willowbrook. Lots of opossum activity above pond. One followed some distance: mostly a steady walk, centers of track-pairs 1 hand-span (8″) apart, and in a straight line. When a curving turn made, tracks became very close together; more erratic in appearance. Altered route slightly to get around sticks, tufts of grass, etc., that could have been stepped over with a little effort.

12FE06. McDowell Grove. I picked up an opossum trail in the snow, the animal having come up from the West Branch. Snow had fallen before its walk, and then during the opossum’s wanderings, as the tracks had less and less snow in them and ultimately none at all. It occasionally dug in leaf litter, was interested especially in areas around fallen logs and at the bases of large trees. Den in a rotted out cavity in the base of a standing tree, near the trail junction where a former bit of landscaping was done in the northern part of the preserve. Den entrance photographed.

24FE07. A large opossum walking through woods at Blackwell, far from any feeders, at 9a.m.

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