Striped Skunk Dossier

by Carl Strang

As striped skunks complete their mating season, this seems an appropriate time to share my dossier of observations on the species.

Skunk, Striped

Striped skunk

Striped skunk

I rarely saw skunks around Culver as a child, perhaps because of their nocturnal activity pattern. Saw one on a road south of town near S.R. 110 while on a run, at dusk, as a teenager. I took plaster castings of tracks at the Bird Sanctuary, Culver Military Academy. Later I saw some in the early evening, visiting picnic grounds at the state park on South Mountain in Pennsylvania. They moved with a somewhat rolling, unhurried walk. Individuals brought to Willowbrook in live traps almost invariably spray as soon as the trap is opened. The spray has a very sticky, lasting quality, and causes a sickening sensation when fresh and concentrated. Youngsters discover their spray ability when 6-9 weeks old. The distinctive black and white color pattern almost certainly is aposematic. That pattern is highly variable in detail, i.e., width and length of stripe, amount of white on head, and number and position of scattered small white spots. The skin beneath is white or black, corresponding to the fur color. Stomping, used as a threat, essentially is an emphatic dancing from one front foot to the other. It is employed against both conspecifics (littermates) and potential predators. The tracks have 5 toes showing, both front and back feet. In suitable substrates, the toenails of the front feet register distinctively distant from the ends of the toes. When toenail marks are missing, the track gives the impression of a miniature cat track (though with the extra toe). Generally, the entire footprint appears as a solid, unlobed block; creases across the soles of the feet are evident in medium-consistency substrates. Tracks rarely are encountered, however. Apparently there is very little activity in winter.

Skunk tracks, hind on left, fore (showing long toenail marks) on right

Skunk tracks, hind on left, fore (showing long toenail marks) on right

17/18FE86. I followed a fresh skunk trail. Gaits in deep snow (4-8″) were diagonal walk and lope, primarily, on an early spring ramble. This skunk ate some mushy crabapples from the previous fall. It went about half a mile on Willowbrook preserve plus an unknown distance on adjacent properties. The den (near Willowbrook picnic grounds) was a tunnel dug in a well-drained location, on an east-facing slope, sheltered by a crabapple. Tracks suggest it was shared with 1-2 cottontails.

4NO86. Diagonal walk in mud, probably the same skunk described in the previous account, at rehab area west gate.

28NO86. Sand seems to stick unusually well to the flat soles of a skunk’s feet, deposited on sticky mud to form roundish or oval spots of sand grains (Culver Fish Hatchery).

29NO86. Memorial Forest near Culver. Lope (bound?) In sand, 6″ between sets of tracks, each set 12″ long.

Sketch of track patterns in the string observed on November 29, 1986

Sketch of track patterns in the string observed on November 29, 1986

28JA87. One or perhaps more than one skunk on walkabout last night in Willowbrook Back 40. Paths extremely convoluted and interweaving, not enough time to sort them out. No skunk came out of the picnic grounds burrow.

3FE87. Skunk on walkabout again, same area. Suddenly it seemed to be taking great leaps. The snow crust froze in open spots at night, so the skunk did not break through in those places.

5FE87. Skunk pulled dead shrew (previously cached by fox) to center of trail but left it.

27OC87. A skunk ran across the road in our Warrenville neighborhood (Summerlakes subdivision) in early evening (around 6pm). It elevated the middle of its tail, giving it a strange, double-humped appearance.

18OC88. In Cactus Camp prairie, tracks show where a skunk dug out a yellow jacket nest recently. A few wasps still were flying in and out.

12JA89. A dead skunk on Park Boulevard at Willowbrook, came out mid-winter.

8SE89. Skunk diagonal walk, flat soft topsoil. Hind foot landing in front of and slightly overlapping front foot. HF 1-5/16″ wide x 1.25″ long.

8JA90. Willowbrook. On the night of the 5th or 6th, a skunk was out. Those were warm nights.

7MR90. Willowbrook. Skunks have been very active the past couple of nights. One has a burrow at the south edge of Willowbrook preserve, south of the stream. They made a couple stream crossings (water, not ice). One of these continued straight north all the way across the preserve.

Typical bounding gait pattern

Typical bounding gait pattern

1SE90. As I ran on the Prairie Path in Warrenville near the library in early evening, what appeared to be a large cat emerged from the vegetation at the side and then stopped in the middle of the path as I approached. Thinking to frighten it out of the way, I began to snap my fingers and accelerated. The cat was strange…it seemed to change shape. Then I saw the stripes and quickly backpedaled. It was a family of skunks, so tight together they seemed one animal in the distance in the dim light. There were at least 3 young with the mother. They had stopped and faced me, partly lifting their tails, all of which made the stripes easy to see even in the darkness. After I backed off they continued on their way.

25FE99. I found a skunk den in the far NE corner of the new Willowbrook preserve addition, under a pile of stacked old telephone pole segments. As many as 4 skunks were active on the preserve the previous night.

16FE00. A skunk on walkabout at Willowbrook last night, the first sign of skunk activity this winter there.

12SE05. Caesar Creek campground, southeastern Ohio. There is much evidence of skunks in the area. In the dusk, a large beautiful individual whose broad back stripes had joined, giving it a white back with just a little black between on the lower back, passed my campsite. Later in the dark, a smaller individual was digging grubs in the lawn of the adjacent campsite. This one was all black with a tuft of white on the head and another at the tip of the tail. It turned away when I shined a light in its eyes, coming as close as 15 feet. It moved slowly, its head sweeping back and forth sniffing, but when finding something to dig it moved quickly, excavating and moving on within about 3 seconds. The next morning I took photos of some of the holes, and of a pile of scats. The holes were mostly neat, ½” diameter, dug out on one side with toenail marks clear, occasional larger ones up to 2” diameter. The scats were stacked weasel fashion, each ½” diameter X 2” long, 3 pieces, one broken with a tiny root sticking out.

One of the holes described on September 12, 2005

One of the holes described on September 12, 2005

The scats described on September 12, 2005

The scats described on September 12, 2005

19JA11. Mayslake. From the night before last, which was the warmest this month (only dropping into the 20’sF), tracks of a skunk. It may have originated from the known den in the north stream corridor. Its winding trail covered much of the north stream corridor prairie, parts of the main prairie, cut from the small savanna at the north end of the prairie across the driveway’s turning circle into the strip of vegetation along the west edge of the preserve, wound through that as it worked its way north, eventually crossed the driveway again at the 31st Street Woods, and continued heading east along the north end of the parking lot marsh.

21JA11. Mayslake. I went to the known skunk den hole in the north stream corridor to see if it was the home of the skunk I tracked 2 days ago. It had not been entered or exited. I picked up the skunk’s trail where it had gone around the N end of the parking lot marsh, and followed it to a hole in the top of the ridge between that marsh and the stream (created when the marsh was excavated), and even with the marsh’s center. It appeared that the skunk had emerged and entered the hole, but the tracks were obscured by large ice crystals developing around the hole’s edge.  Later it occurred to me how unusual those crystals were. Are they growing on moisture from the skunk’s breath?

Skunk den entrances usually are around 6 inches in diameter.

Skunk den entrances usually are around 6 inches in diameter.

23FE11. Mayslake. For a time I mistook a skunk’s trail for that of a mink. What threw me off was the first impression, where the toes spread an unusual amount in thin snow over slick ice. I failed to attend the other tracks carefully enough for a long time, though I was somewhat bothered by the long toenails and the animal following the trail rather than the lake edge. As I approached the den near the friary site I saw similar tracks, confirmed much coming and going and digging at that den, then went back and found that if I had paid closer attention to all the footprints I had been following, I would have realized sooner that they were skunk tracks. The main underlying condition was the thin layer of snow over ice, with enough of a percentage of round-looking tracks resulting to sustain my error.

Great Horned Owl Species Dossier

by Carl Strang

Today’s species dossier is one of my largest. Great horned owls simply attract my attention and interest more than most other animals, and so I have accumulated more notes on them. Great horned owls haven’t been as easy to follow in the years since West Nile virus came into our area. Formerly the crows were reliable blabbermouths as to where the owls were. If our local crows develop resistance to the disease, those days will return.

Owl, Great Horned

Great horned owl

My earliest memory of young great horned owls was in a forest near Purdue, after they had branched one spring [branching is the term for owlets leaving the nest; it is different from fledging, because they reportedly climb down to the ground, walk to another tree, and climb up it]. I know this species primarily from observations in DuPage County, IL, where it is the common large owl, occurring in forests, even small ones. A pair nested annually in the Willowbrook riparian strip for many years, staying as year-round residents. They nested in large willows, 20-30 feet up, first in a nest on branches, then after a storm dislodged the nest, on a provided platform until that tree fell. Incubation begins January or February. The non-incubating male bird usually perches nearby in the daytime, flying away apparently to draw off people or mobbing crows. Owlets (usually 2) branch in May as trees are leafing out, can fly between trees by late May. Young have a distinctive begging call, a rising squeaky-scraping or -grating loud “scaip!” Young disperse usually by the end of October. Before then, they fly all over their parents’ territory, usually staying fairly close together. Branched young mostly sit still, observing all that goes on around them. November brings frequent late afternoon and evening territorial calls: the female’s call is a higher-pitched “WHO-whowhowho-whowhowho-who.” The male’s call has fewer syllables and a lower pitch.  Deep, booming voice. Willowbrook’s territorial birds had a running, never-ending conflict with the caged birds. I also heard calls during childhood campouts on the Tippecanoe River, Indiana, in summer, and later in the woods near the Boiling Springs, Pennsylvania, house in spring.

Pellets and food remains in late winter 1986 at Willowbrook were heavy in rabbit fur and bones in February, meadow voles in March. There were feathers of a gull in May. They covered a territory that included Willowbrook, adjacent residential neighborhoods, and much of the College of DuPage campus, for a total of perhaps 100 acres.

In the Basin of the Chisos Mountains, Big Bend National Park in Texas, they were calling around 5:30am in late July. We saw others there on the road in early evening in the upper desert. They were a bit paler than Midwestern birds.

Some contents of owl pellets at Mayslake, 2009. Prey species are meadow voles, white-footed mice, and a short-tailed shrew.

12FE87. Lots of recently molted breast feathers in Willowbrook Back 40.

8AP87. Photos of branching young owls.

Great horned owl, soon after leaving the nest.

29AP87. Crow remains found under nest area.

5MY87. The pair’s own nestlings now branching, in a willow 50m from nest tree.

6MY87. Remains of a consumed pigeon.

7MY87. The young are in another willow, closer to the nest tree, the one used most by last year’s young when branching. The third (foster, added by Willowbrook staff) youngster is on another branch of the same tree.

8MY87. Another tree change.

1JE87. The young are flying.

5OC87. Adult male beginning to hoot, in afternoon, Willowbrook Back 40.

9JA88. McDowell. Owl flushed from pine grove at south end of north field.

16JA88. McDowell. A great horned owl flew to tree on the west bank of the river, just north of where trees thin to a thread of willows, and where a housing development comes down to the river. There’s a top-blown tree nearby, also several large oaks. Then crows began raising a ruckus nearby in another direction, as though pestering a great horned owl. From that direction a red-tailed hawk soared, but they paid it no heed. It circled an adjacent riparian strip, but when the owl finally broke and flew with a flock of 10 crows in pursuit, the hawk fell in between, and also began to chase the owl. Once it got above the owl and swooped at it, brushing the owl’s back with its feet, but about then the crows caught up and chased both raptors down toward where I had seen the first owl perched, now out of my sight.

30MR88. Willowbrook. Fresh pellet with remains of 2 meadow voles.

25AP88. Both great horned owls off the nest, though in nearby trees.

17MY88. I hadn’t seen great horned owls of Willowbrook Back 40, or heard harassment by crows, in some days. Today I saw 2, upstream of their nest. Crows didn’t harass them for long or in numbers (2-3), apparently too occupied with their own nesting activity.

18JE88. Harassment of owls by crows gradually has increased this month at Willowbrook. Today I observed heavy harassment of a great horned owl by a large number of crows at McDowell Grove F.P. Owls branch at the same time crows are starting to nest, and becoming too busy to harass owls.

22FE89. Owl on a nest at Willowbrook (started incubating within the past 10 days).

26AP89. For the first day since February, there is no adult owl in the nest tree at Willowbrook (have been brooding several days, then a few days of adult perched beside nest with a youngster visible. 2 young. A fox squirrel climbed the nest tree. When it was just below the nest, the adult female flew from a nearby willow, and landed on the nest. The squirrel turned around and began to climb down as she flew in, but was not panicked.

31AU89. Jays vigorously “jay”-ing at an owl well hidden among leaves in a willow top. Chipmunks chucking nearby, below.

30NO89. Great horned owl flying, viewed from behind. Wingbeat of remarkably little amplitude, compensated by its more rapid rate. A fluttering sort of appearance. Wings kept straight. (A behavioral quieting of flight?)

14DE89. Willowbrook nature trail. The owl caught a mouse, according to tracks. Slight blood drops in snow. Many steps trampled snow just beyond the mouse burrow. Then the owl walked, either having swallowed mouse or transferred it to bill. Tracks: landed on mouse tunnel, then walked 5m. Noticeable straddle, up to 1 inch. Track 4 inches long, 3.5 wide, right angle toe pointing to outside distinctive for species. 8 inches center to center for length of step between tracks.

Sketch of great horned owl tracks.

3JA90. The Willowbrook owl pair perching near nest platform.

29JA95. Following a tip, I found a great horned owl on a nest at Maple Grove F.P. Stick nest was built last year by Cooper’s Hawks, according to informant. Nest solidly based in a main crotch 15-20 feet up. Owl had head and ear-tufts up, very noticeable but only from the front. Nest tree right beside a regularly used trail, but not a main trail, less than 200 yards from Maple Ave. and less than 100 yd. from the private school on the east border of the preserve. The owl reportedly has been on the nest less than a week.

18FE99. At Willowbrook, I found this year’s great horned owl nest (they probably have used this site before; not easy to find) in the top of a dead tree trunk, with most of branches gone, a large hollow with little in the way of a roof. Only part of the owl’s head is visible, and only from certain angles. A single fuzzy feather tuft was the give-away. Once while I watched, the bird appeared to stand and turn or shift eggs by moving feet, stepping from one to the other. The owls had been advertising consistently in the area around this tree in the early winter. Crows mobbing nearby earlier in the day (presumably after the non-incubating bird nearby) drew my attention to this area. Only one other candidate tree is nearby.

A sketch I made after finding the nest on February 18.

11MR99. The great horned owl was standing in the Willowbrook nest in the morning.

15MR99. A young bird was seen on the afternoon of the 12th. Today at least 2 young are visible. They were being fed between 3 and 3:30pm.

18MR99. The 2 young owls frequently are standing in the sun in the nest.

12AP99. The Willowbrook great horned young have branched.

A pair of branched young.

16AP99. One of the owl young somehow crossed the rain-swollen Glen Crest Creek to perch between it and the Nature Trail. Flew?

4MY99. At mid-day, a flock of 8 crows pursuing an adult great horned owl over much of Willowbrook Preserve.

27MY99. Both Willowbrook owl young still alive.

11AU99. Only one of the Willowbrook owl young remains.

18AU99. The young owl calling at mid-morning.

8MR00. A neighbor near the north edge of the Willowbrook preserve reported that the pair of great horned owls have been calling in his yard nightly since late January. He gave us permission to look for a nest, and we found it, in the top of a large blue spruce, built on an old crow or squirrel nest. 20 minutes were required to find a small hole through which to confirm the bird’s presence. The tree, perhaps 40 feet tall, is close to a dead‑end side street, in between his house and garage (the 2 buildings less than 20 feet apart), with no other tall trees right there though several others were in the yard. The bird appeared still to be incubating, occasionally turning eggs. We did not see the non‑incubating owl, but numerous potential roosting sites are nearby.

30MR00. We checked the nest again. After a few minutes the brooding bird flew away (sunny, warm afternoon). We could see one young bird clearly; there may have been more. Development seems behind last year at this date by at least a week. Still all white down, as far as we could see.

14AP00. In central Kane County, in a bur oak woodlot of perhaps 10 acres, a great horned owl nest. The nest is an appropriated crow or hawk nest in the top of a large oak. At least one young bird still is inside. The presence of the owls was made clear when the adult male flew past us, pursued by crows. He was small, appearing no larger than the crows. Later I found the nest when walking through the woods. The female flew a short distance, and a few crows called, but she settled in against the trunk of an oak, well camouflaged, and they left her alone.

17JL00. No sounds of great horned owl adults or young at Willowbrook in the evening.

2001: No signs of nest or young around Willowbrook this year, though in the spring an adult seemed to be decoying crows.

Great horned owl tracks. Owl tracks are distinctive in having one of the toes protruding out to the side at an odd angle.

14SE01. An owl called several times in the early dusk at Herrick Lake, south of the former youth campground. I see that this is my earliest record of territorial behavior, by about 3 weeks.

3NO01. Saw an owl, probably a male, at Herrick Lake F.P. in the forest behind a house, north of the big trail loop and south of the former youth group camp. That was in the morning. In the late afternoon, heard one hooting along the Fox River somewhere around Red Oak NC.

27SE02. While walking after a run at Herrick Lake, heard both members of the pair duetting strongly for at least 5 minutes (same area as previous 2 entries).

13FE07. At mid-day in the middle of a winter storm with heavy blowing snow, a great horned owl at Fullersburg holding a recently caught gray squirrel.

3AU08. Great horneds called for a long period, early morning, in my neighborhood. This continued into the dawn hour and overlapped with a cardinal’s singing, past 5 a.m.

21JA09. Mayslake. An elm branch, apparently broken from tree by storm, with bark being consumed by cottontails. Near there, one of the rabbits caught and consumed on the spot last night by a great horned owl (impressions of wing and tail feathers in the snow). Head, feet, a couple bones, and fur all that remain.

29JA09. Mayslake. I found where a great horned owl had walked on the frozen stream surface, heading S out of the woods, taking off before reaching the bridge. The tracks led back to a feeding site, with much cottontail fur and a bone, but no rabbit tracks. Continuing downstream 20 yards I found another area against the bank with fur and blood, and a couple great horned owl footprints again from last night, but again no rabbit tracks. On downstream another 30 yards I found yet a third such site, but again no rabbit tracks. Here there was no feeding, mainly just the impression of the rabbit in the snow. As the owl had walked a few steps before that impression, it must have had the rabbit in its beak. The owl had come from the N or NW. I searched all around but did not find a clear kill site. All of this was under trees with moderately thick brush that makes it seem unlikely the owl would carry prey in there from outside. The shift of location twice would seem to reflect a sense of vulnerability. I wonder if the owl would have removed the head and feet at the actual kill site. The body impression where it first landed on the stream ice was bloody.

Here is one of the stops made by the great horned owl described in the January 29 entry. There is an oval depression where the rabbit’s body was placed.

14FE09. Fullersburg. This year the great horned owls are nesting in last year’s Coopers hawk nest, just west of the Amphitheater. That nest has been available both the past two years, but the owls have chosen to use other hawk nests close to 31st Street in all of the previous 4 years but 1. In that year there were reports of a nest well south of the preserve, but I could not find one on the preserve.

19FE09 Mayslake. I found the great horned owl nest in a hollow willow near the west boundary of the preserve close to May’s Lake. It is not high up, and exposed thanks to the brush clearing, but facing away from the lake may limit its discovery by fishermen.

Great horned owl incubating nest in tree cavity, Mayslake, February 2009.

6MR09. Mayslake. Great horned owl is standing in the nest cavity, apparently brooding.

13MR09. Mayslake. The great horned owl nest tree snapped off at the point of the nest cavity, presumably in the wind storm 3 nights ago (gusts reached 45mph). A dead owlet at the base of the tree, none others nor adult seen, no sign of hurt adult but nest apparently abandoned (cold enough today that an adult would be brooding). There has been enough time that scavengers could have removed other young.

Dead nestling beneath storm-broken nest tree.

10DE10. Neighborhood. I heard a great horned owl calling early this morning.

27JA11. Mayslake. Great horned owl incubating on last year’s red-tailed hawk nest. It was not there yesterday.

Great horned owl incubating nest, Mayslake, January 2011.

10MR11. Mayslake. The owls have abandoned the nest. No sign of disturbance or dead nestling beneath, best guess is the eggs didn’t hatch, either infertile or perhaps the female was forced to abandon during the fierce blizzard at the beginning of February.

18MR11. Mayslake. At a bright mid-day, the great horned owl pair duetted for more than 15 minutes, the male in the west end and the female in the east end of the area 9 hilltop pines.

29MR11. Mayslake. A single hoot from GHO in pines, mid-day, the first I’ve heard since the 20th.  (In September I heard the pair duetting at Mayslake, so they remain at the preserve.)

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.

Dead Vole Mystery

by Carl Strang

Perhaps a minute after leaving the snake I described yesterday, I encountered a small dead mammal lying on the trail.

What makes this finding of a deceased meadow vole surprising is that Mayslake Forest Preserve has no shortage of predators who include these little guys on their menu. Typically all that would be left would be bones in a raptor pellet or fur in a scat. I saw no signs of damage on the vole. Two most likely scenarios come to mind. First is that a well fed neighbor’s cat killed the vole and left it, the needle-like toenails and canines producing no obvious trace of their work. I haven’t seen any cats or their signs around lately, but I’ve known cats that were very good at staying out of sight. The other possibility is that the vole was victim of a short-tailed shrew’s poisonous bite, but some circumstance separated the shrew from its prey. Though I have no solution to this mystery, it’s enjoyable nevertheless to find such things and think about them.

Literature Review: Short-tailed Shrew Venom

by Carl Strang

In an earlier post  I mentioned the salivary poisons of short-tailed shrews. A paper published last year reported an analysis of the venom.

Harvard University (2009, November 2). Venomous Shrew And Lizard: Harmless Digestive Enzyme Evolved Twice Into Dangerous Toxin In Two Unrelated Species. ScienceDaily. Retrieved November 3, 2009, from­ /releases/2009/10/091029125532.htm

The paper’s authors, Yael T. Aminetzach, Hopi E. Hoekstra, John Srouji, and Chung Yin Kong, published in Current Biology. They found that the short-tailed shrew’s venom is a derivative of a digestive enzyme (kallikrein). The version produced in the salivary glands is more active, making it poisonous. The Mexican beaded lizard’s bite venom is a different variant of the same digestive enzyme, having evolved independently.

The science of evo-devo  has produced concepts that shed light on these results. Every cell in the shrew’s body contains the same genes, including that for producing kallikrein. At some point in the past, apparently the very distant past, the common ancestor of shrew and lizard (and us!) used this gene only for digestion. The steps to today include the production of a modified version of the enzyme, the increased toxicity of the modified version, and its production by the salivary glands. These steps happened twice, in the two distantly related species.

In the earlier post I mentioned that the shrew’s poison renders it distasteful to predators. I had thought that there were levels of the poison in the shrew’s tissues, but now I wonder if they simply are applied to the shrew’s fur when it grooms itself.

Red Fox Dossier

by Carl Strang

This is another of my species dossiers, consisting of what I know about a given species from my own experience. I started the dossiers in the mid-1980’s.

Fox, Red

Initial summary: Common resident of mixed fields, brush and woods edges in northern IN, northern IL, south central PA. Also seen on tundra in western Alaska. Near Culver, IN, seen most commonly in winter, when they are frequently active and visible at a distance during the day. In summer, occasionally flushed from resting spot beneath a bush in an old field.

In Alaska they foraged for mice, birds, eggs and young waterfowl in summer. In tall sedges they attempted to pin birds and mice by listening for them, then leaping high and coming down with front legs together and extended straight down. Cached eggs singly, burying them near where found.

Den found on 2AU71 in high bank of tundra lake in bluffs area near Kokechik Bay, western Alaska. Entrance faced south. Well worn paths leading to water 15 feet below and to top of bluff 7 feet above. Entrance about 1 foot in diameter. A second entrance on top of hill. Fish remains.

At Blackwell Forest Preserve, in June, their contact calls heard at night: a high-pitched whining scream or “yipe,” beginning and/or ending with a harsher, rougher, strangled sound. In May 1986, on a walk through the forest at the Morton Arboretum, DuPage County, IL, I felt the need to freeze. Soon a yellowish-colored apparition came toward me, following a dry streambed that passed 30 feet to my left. Soon the red fox came into clear view, a chipmunk dangling from its jaws. It was walking fairly quickly and directly, not looking from side to side. Chipmunks gave single “chip” calls and were silent as it passed. It went by me, then after another 20-30 yards came to a sudden halt, spun around, and at a faster speed came back past me. I suppose it had caught my scent where I crossed the stream.

Trot on thin layer of snow over ice. Width of entire path 5 inches. Travel left to right.

           RF                               LF

RH       o                    LH      o

 o                               o         

     3.5″        10″              3.5″

13JA87. Red fox bed in Willowbrook Back 40. Snow 6″ deep, was compressed in a 15″ diameter area. May have been flattened with feet first. No hair, but claw marks in bottom of bed probably from stretch as the animal prepared to leave. Bed in area where brush slightly denser than average, and concealed well by grasses on one side. Photos next day after some melting (bottom of one part melted out). Odor of fox evident on day it was made, not detected following day.

17JA87. Red fox lope. Front feet bigger, back feet have rounder heels. Body held at an angle to direction of travel.

LF       RF                              

 o         o                     RH       LH

                                      o         o

4FE87. Fox at Willowbrook cached a short-tailed shrew, and apparently stopped by later to check on it.

6AP87. Willowbrook fox still present.

17AP87. I saw the fox.

27JE87. McKee Marsh area. A red fox passed just north of sawdust storage pile. In thin summer fur. Saw me as it came even with me, 50m away (I was standing, but still), and it ran into tall vegetation.

23DE87. Fox swam across Glen Crest Creek at Willowbrook several times in recent days.

3JA88. McDowell Grove Forest Preserve. Several pictures of newly excavated fox den, with rabbit remains at entrance. In gravel bank above floodplain of stream.

9JA88. The McDowell fox has used the river ice intensively as a corridor and for crossing (tracks especially heavy opposite den).

15JA88. Followed Willowbrook Back 40 fox’s wanderings through last night’s inch of new snow, Back 40. Nearly all the time in steady diagonal walk or trot. Relying on nose for clues? Occasionally deviated to investigate rose bush or brush tangle.

17JA88. Blackwell. Rain melting snow reveals a superabundance of meadow voles (also found 2 dead voles), near where kestrel had picked the one found on the 14th. Predators taking heavy advantage. Fox tracks all over.

23JA88. Alternative trot pattern, body straight with path of travel? McDowell. Even spacing throughout (within and between sets), 12 inches separating (slow lope? But so close together?). Travel left to right.

 LF       LH                   LF       LH

  o        o                         o         o

            o        o                          o        o

           RF       RH                     RF       RH

Foxes highly active last night (rabbits, too). 1″ snow fell just after sunset.

28JA88. Fox tracks in normal walk separated by 14-18″. After 2 full days of no fox tracks, suddenly after last night the Back 40 is filled with them.

29AP88. Fox seen at Pratts Wayne Woods Forest Preserve. Stopped many times to look back at me as it ran away.

10SE88. One seen Herrick Lake F.P. Seemed weak, or perhaps simply expected me not to notice it there.

2NO88. Willowbrook. Tracks have returned to Back 40, after disappearing during summer of marsh excavation and nature trail construction.

15JA89. Red fox tracks at Herrick Lake Forest Preserve: one fox’s set had a pattern for a long distance, on cleared path with ice and a thin snow cover that had partly fused to it, of a mix of walk and trot, i.e., two walking steps and a trot step.

24MR89. Winfield Mounds, tracks. Red fox moved from walk to trot (body angle version). Step increased from 16″ to 18-19″, and more on toes.

22JE89. Scats in Willowbrook Back 40 packed with mulberry seeds. The berries first ripened within the past week.

7SE89. Red fox tracks near marsh. Fox also crossed Park Boulevard last night.

8SE89. Back 40, fox walking stride average about 16 inches, heel to heel.

19NO89. Tracking coyotes in half inch of snow that fell last night on McKee Marsh area. Ponds frozen. Coyotes’ activity heavily on and around them. Frequent rolling, sometimes in urine. Fox tracks absent from wide area I walked in N. Blackwell. Were common before; have coyotes driven them off? (In late 90’s, foxes resurging; researchers say mange took them out).

20NO89. Red fox tracks, Willowbrook, soft soil (but true track size) 1 5/8L x 1 3/8 W.

14DE89. Willowbrook. Fox direction of travel when track partly filled with snow: slides foot in at an angle, lifts it straight out. Covered a lot of ground last night. Played a while with the caged fox. Below 0°F last night. Rabbits, mice and a muskrat active.

16DE89. McDowell. Foxes and coyotes present. Foxes about 12-16″ between steps in walk, coyotes 15-20.”

19DE89. Willowbrook. Fox carried stiff dry weed stem 1.5 feet long for some distance, dragging end in snow. Play? Were mink doing same at Herrick and McDowell last winter?

21JA90. West Chicago Prairie, on Prairie Path. Fox slow lope, maintained considerable distance. 9-14″ (variable) between footprints, tend to be greatest from the Left front to the pair of tracks. Gait developed out of a trot, body-angle version, with 11-12″ between pairs of tracks and 2″ (along axis of travel) between the members of a pair. The slow lope appears to be a common gait along here today, either an individual preference or controlled by the quarter inch of snow that had fallen earlier.

          LF       LH                  

            0         0                      0        0

 0                     0          0                    0

RH                   RF                              

26JA90. Willowbrook. 4 inches of snow dumped in heavy wind yesterday. Last night wind calmed. Sticky snow on all plants. Mice and foxes, some rabbit activity. Fox taking longer (16-24″) walking steps. Lifted leg to mark (male?). A common slow lope pattern, so similar to the diagonal walk as to be almost indistinguishable in this snow depth. Appear to be LF, RF+RH, LH. Space between sets of 4 tracks slightly greater than spaces between. Travel left to right:

 o                    o                    o                    o

          o  o                                      o  o

(actually, slightly longer hole in snow where right feet are close together)

22AP90. Winfield Mounds. Tracks near SE corner of preserve, near houses.

26JA92. Hidden Lake. A red fox in forest bedded for a time atop a fallen log, bed 8″ diameter at bottom, 12″ diameter overall. Fox removed a bit of a burdock bur with some hairs. Bed 2.5 feet above ground, on a hillside. Fox had walked along top of log to reach the spot.

From 1993 to 1997, red foxes were scarce in DuPage County. I don’t remember seeing any on the preserves during that period, and essentially no signs. Coyotes, meanwhile, became abundant. Beginning in 1998, I began seeing red foxes again. Coyotes remained abundant.

1AP00. Red fox scats on Heritage Trail, Morton Arboretum, near its southern boundary with Hidden Lake Forest Preserve.

In the 2000’s I seldom have encountered red foxes or their signs. Based on reports from phone calls to the forest preserve district, and occasional sightings of my own, I have the sense that red foxes now are mainly animals of residential neighborhoods, and are much less common than they once were in the county. Their place on the preserves has been taken by coyotes.

Short-tailed Shrew

by Carl Strang

A few days ago I saw my first two short-tailed shrews at Mayslake Forest Preserve. Both were dead.

short-tailed shrew b

This one was in the middle of the trail. The other was in a mowed area, a few feet out from the edge of a prairie. These almost certainly were killed by coyotes. They appear to have been left as calling cards in the same way that coyotes deliberately place their scats in the centers of trails. Other coyotes coming along are sure to find them and know the area already is claimed.

I knew that short-tailed shrews were on the preserve, compliments of a great horned owl.

Owl pellet 1b

These skulls all were in a single owl pellet deposited in the center of the preserve last winter. The upper left one belonged to a short-tailed shrew. So, why would the owl eat these shrews, while the coyote leaves them after killing them? After all, if the coyote wants to use a small mammal as a marker, there are many more voles and white-footed mice, so we might expect the coyote to use them as markers, too.

Here I have no inquiry I can do myself. I must rely on what others have found. It turns out that short-tailed shrews are toxic. They have salivary poisons that help them subdue the voles that often are their prey, but some poisons are found all over their bodies. Owls, with their relatively poor taste and smell, gulp down any they kill (great horned owls also eat skunks, by the way). Coyotes are less inclined to do so. They pounce and kill a small mammal moving through the tall grass, then find it’s a shrew. Being resourceful while not wanting to eat something so vile tasting, they use it as a marker. At least, that is what I think is happening here. Another possibility is that the coyote deliberately kills the shrew with the intention of using it for communicating with other coyotes, incidentally taking out a competing predator.

Owl Pellet

by Carl Strang


Recently I picked up a fresh owl pellet at Mayslake. I say, “owl,” though I suppose it could have come from a red-tailed hawk. The size, shape and location of this spit-out ball of fur and bones were much more consistent with the resident great horned owls, and I am confident that was the predator. I have written before about these owls as predators of cottontails, but this pellet allowed me to add three more species to the prey list.




Upper left is the skull and both halves of the lower jaw from a short-tailed shrew. This small mammal has toxins in its body, but clearly they didn’t deter the owl. Upper right are two skulls from white-tailed mice. I did use the magnifying glass to be sure, but a deer mouse at Mayslake would be something of a surprise. The remaining four skulls came from meadow voles. In this case I double checked against the unlikely possibility of prairie vole.




All seven small mammals would have been consumed within a reasonably short period of time. Each was just a single swallow for a bird this size, but together they provided a sufficient meal for an evening’s hunt. The pellet was in the middle of a brushy woodland, but that was not where all the hunting was done. Though white-footed mice and short-tailed shrews often occur in woodlands, the several meadow voles testify to a more open, meadow or prairie habitat. White-footed mice and short-tailed shrews also frequent such places. The pellet was in the center of the preserve, and I feel safe in my belief that these small mammals all were caught within Mayslake’s boundaries.

Sketching Mayslake’s Trophic Structure

by Carl Strang



As I familiarize myself with an area, there are several big conceptual nets with which I try to comprehend that place. These lack fine detail, but provide first approximations that can be filled in as I learn more. One conceptual frame for an area is its general topography and drainage pattern. Another is the general human history and influence on the land. A third is the mosaic of vegetation communities. A fourth is the geology. Today I want to focus on yet another frame, the trophic structure. This is a broad-brush first stage in constructing a food web. The trophic levels of an ecosystem are the steps through which energy “flows” (the quotes are a field ecologist’s recognition that abstract food pyramid diagrams, and the arrows that connect food web elements on the page, cover up a certain amount of desperate flight-and-chase, crunching, and screaming. All our lives continue at a cost, but I digress).


In earlier posts I have documented some of Mayslake’s animal life. The top predators mentioned already include coyotes and mink. A day seldom goes by without me seeing a red-tailed hawk or two. I also have seen tracks of great horned owls, and the Mayslake staff have observed these birds at that preserve for years.


Great horned owl tracks, Mayslake

Great horned owl tracks, Mayslake



Note that in this photo, the great horned owl tracks are farther apart than in the photo I took on the Christmas bird count. This is the more typical spacing, but again there is that odd asymmetry in the toes.



Mayslake’s part-time predators include raccoons and skunks, among others.


Skunk tracks (far right), Mayslake

Skunk tracks (far right), Mayslake


On a smaller scale, I have seen tracks of short-tailed and masked shrews, which are predators of small animals including invertebrates but also mice.


Common plant-eating animals at Mayslake include deer, mice, voles, squirrels, chipmunks and cottontail rabbits. There are also the wandering winter birds eating seeds (as in the paper birch account).


Rabbit trail, Mayslake

Rabbit trail, Mayslake



Over 50 kinds of trees, shrubs and vines, along with uncounted herbaceous plants, are the preserve’s primary producers, solar energy harvesters that form the foundation for the whole trophic shebang. In the warm months, each kind of plant hosts several insect consumers that in turn are food for predators including an influx of migrant nesting birds.


And let’s not forget the scavengers. Some of the animals listed already, the coyote and skunk for instance, along with opossums such as the young one whose tracks I saw in the southern part of the preserve recently, are happy to clean up the odd dead carcass they encounter.


Mayslake is not a huge property as forest preserves go, but it’s big enough and diverse enough in vegetative structure to support a complex community for which I have here provided only the broadest of introductory sketches. More detail to come.

Alphabet of Tracking: 5 Toes Front and Hind Feet

by Carl Strang


Today I continue my tracking primer with a focus on mammals whose feet typically show 5 toes on the front and hind feet of complete tracks (but remember that in the field you often have only partial footprints; this is where dirt time comes in, as mentioned in the last post). Local animals in today’s category are raccoons, opossums, members of the weasel family, and shrews. Bears also are in this category, though they are even less likely than mountain lions to show up in northeast Illinois.


Black bear track

Black bear track



Raccoon tracks have long, round-tipped toes and are among the most frequent footprints we notice, because these are common animals, they often are passing through muddy areas, and they are heavy enough in body to sink into the surface.


Raccoon track

Raccoon track



Opossum tracks are, like the animals themselves, amazing and odd. Typically the hind foot is rotated so that it is oriented sideways, wrapping around the heel of the front foot with the big toe pointing in and the other four pointing out. The toes on the front foot are spread so widely that the overall effect reminds me of a star.


Opossum tracks

Opossum tracks



Our most common local weasel family representatives are the mink and the striped skunk, but I remain alert for otters as well. Mink tracks have a round appearance overall. Though primarily aquatic animals, their footprints often turn up away from water (in DuPage County it is not possible for them ever to be truly distant from water, however).


Mink tracks

Mink tracks



Otters likewise are aquatic. Their tracks are bigger, and they likewise can travel distances over land between water bodies. (I am deliberately not including size measurements. I have to leave something for your own inquiry!). I have not encountered an otter in DuPage County yet, but given the success of the program re-introducing them to the state I regard this as simply a matter of time.


Otter track

Otter track



Striped skunk tracks at first glance often remind me of domestic cat tracks, except that five smaller toes are crowded into the space of the cat’s four. Skunk tracks have toenail marks, with the longer toenails of this digging animal’s front feet prominently in front of the ends of the toes.


Striped Skunk tracks

Striped Skunk tracks



Shrews are tiny animals. Most of their tracks you encounter will be in snow, and so will not show the individual toes. Masked shrews are much smaller than mice, and so their sets of tracks will be smaller (quarter coin provides scale; the photo includes an entire set of four footprints to the left, and another to the right of the coin).


Masked Shrew tracks

Masked Shrew tracks



Least shrews likewise are tiny, but these are much rarer than masked shrews. Short-tailed shrews often show a diagonal walk gait pattern (to be explained once we reach the “word” level of this introduction).


(probable) Short-tailed Shrew tracks

(probable) Short-tailed Shrew tracks


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