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.

Pale Indian Plantain in Winter

by Carl Strang

In my review of Mayslake Forest Preserve’s plants in winter I don’t want to neglect the woodland species. Today’s plant is a very tall savanna forb, the pale Indian plantain, which is beautiful in summer and in winter. Here is its appearance when in bloom.

The next photo does not give full justice to its winter elegance.

There is a group of these in the small cluster of trees at the south end of the prairie, close to the roundabout circle of the entrance drive.

Literature Review: Owl Throat Patches

by Carl Strang

This week, another paper from last year’s PLoS ONE online journal.

Penteriani V, Delgado MdM (2009) The Dusk Chorus from an Owl Perspective: Eagle Owls Vocalize When Their White Throat Badge Contrasts Most. PLoS ONE 4(4): e4960. doi:10.1371/journal.pone.0004960

Though this paper focused on a European species, clearly it is relevant to our own great horned owl. I cannot do better than to quote the authors’ abstract.

“We investigate here a novel hypothesis on why nocturnal birds with patches of white feathers call at twilight. We propose that white plumage patches and the timing of visual signaling have co-evolved to maximize the effectiveness of social communication such as the dusk chorus. This hypothesis centers on the recent discovery that eagle owls can adopt specific forms of visual signaling and is supported by the observation that adult eagle owls possess a white throat badge that is only visible during vocal displays. By monitoring the calling of eagle owls at dusk, a peak time for bird call output, we found that white throat badges contrasted most with the surrounding background during the owls’ twilight chorusing.

“Crepuscular and nocturnal species appear to have evolved white patches that, shown in association with vocal displays, allow them to communicate in dark surroundings. The evolution of a white badge that operates jointly with call displays at dawn and dusk may be relevant to the eagle owls’ social dynamics. Our explanation for the dusk chorus may possibly represent an overlooked but common pattern of signaling among crepuscular and nocturnal birds that combine patches of white feathers with twilight displays. Furthermore, our findings could be relevant to songbirds that breed in dark forest habitats and have contrasting white badges, as well as birds living in open habitats and showing contrasting bars.”

As my photo shows, the white throat patch on a great horned owl shows at times other than display.

The Shape of Salt Creek

by Carl Strang

Back when my office was at Fullersburg Woods, I had two occasions to study old maps and aerial photos of that forest preserve. Both when looking at the history of periodical cicadas in DuPage County, and when examining Fullersburg’s archeology, I found myself comparing original survey maps from the first half of the 19th Century to the 1874 county atlas to the earliest aerial photos from 1939. Though not central to these investigations, I couldn’t help but notice inconsistencies among these maps and photos in the shape of Salt Creek. Let’s begin with the 1939 aerial photo and work back.

Salt Creek enters Fullersburg in the upper left (NW) portion of the photo when it passes beneath 31st Street. The stream proceeds south, with the interruption of a small hairpin turn, before turning east. After a significant straightaway the stream turns back north, takes a big swing east and divides to surround Willow Island as it begins a long stretch flowing south, then turns SE until it exits the preserve soon after passing beneath York Road. Salt Creek today has essentially the same configuration. Let’s look next at the 1874 atlas.

For the most part Salt Creek looks similar to its present day configuration. There is one significant exception, however. In the next image I superimpose the 1874 map onto the 1939 photo.

The red line I have added to reconcile the two versions. It makes sense. That line traces the bottom edge of a sharp bluff, the edge of the Tinley Moraine. The following photo shows where one end of the adjacent lowland, cut off as the red line shows, meets the morainal bluff.

It appears that the streambed migrated between 1874 and 1939 to create that low peninsula. The concrete slab in the photo, part of an abandoned trail installed during the Great Depression by the Civilian Conservation Corps, bridges what is left of the 1874 channel. Now let’s shift to pre-1850, when the original land survey gives us the first record of Salt Creek’s shape.

This surveyor’s sketch map is based on an original 1822 record. This is significantly different from the later map and photo. Again I superimpose.

The red line again reconciles the two, and again it makes sense. The area along the red line is low, and in fact at times of flood, water sheet-flows through there, short-cutting across the base of the river bend (though most continues to follow the main channel).

What brought this back to mind was an observation I made recently, something I hadn’t noticed before, when looking at the original survey notes associated with the earliest map. The surveyor noted that the width of Salt Creek up and down the stretch now part of Fullersburg was 20-30 links. A link in the surveyor’s standard measuring chain was only 8 inches long, so that Salt Creek prior to American settlement was only around 15 feet wide. Today it’s much wider.

The 1800 width of the stream was closer to that of the central channel through the ice in this photo than to today’s banks. The picture I am left with is of a relatively small stream, wandering over the low area between the Tinley and Valparaiso Moraines. As DuPage County became agricultural, then urban, increased runoff ballooned Salt Creek’s width and volume. The growing stream carved a channel that has become more stable. The change between 1874 and today suggests that Salt Creek at least began to cut its way back to the early-1850’s channel route. However, downward erosion may have set the main channel in a shape that will resist future alteration.

Winter Campfire 15

by Carl Strang

Winter is a time when we slow down and become introspective. Sitting and staring into the fire, we ponder the big questions. If you have been following this blog, you know that the focus here is science, science that can be done simply in outdoor settings. But we are more than scientists, and science has well defined limitations that need to be understood by everyone who does science or studies its findings. This winter I am using one post per week to develop my own viewpoint and biases, in particular sharing my take on the relationship between science and spirituality. In part this defines for me what these two realms of human experience are all about, and also develops the separate methods used for inquiry in each realm. I plan to place this paragraph in front of each entry in this series, so that those who are interested only in natural history or in scientific practice can skip these posts.

What is Meant Here by Spirituality?

I define spirit as an aspect of reality regarded as being incapable of perception through the physical senses in any objective way. It is experienced subjectively, through emotions or feelings, visualizations, artistic inspirations, peak experiences (epiphanies), mystical experiences, etc. Spirit often is thought to underlie and perhaps permeate the physical universe, to be connected to it but not dependent upon it (though the reverse may be true), and to be more essential, more important, or more permanent or eternal. Spirit often is regarded or intuited or perceived as being organized in some way. Various interpretations of this organizing principle lead to the various religions, and so this is as far as the definition of spirituality (attentiveness to spirit) can go without entering the more specified realm of religion. Examples of the organizing principle as it is regarded by different religions are concepts of God (Allah, Great Spirit, etc.) or a group of Gods, a Higher Power more vaguely or impersonally defined, the Great Tao, the Kami of Shintoism, the Spirit‑that‑flows‑in‑all‑things of certain Native American traditions, the Void, there are countless others. Also, the degree to which spirit is divisible (e.g., into more or less discrete “spirits”) varies according to different religious views.

Spiritual experiences appear to be universal, regardless of a person’s religiosity. Alister Hardy (1979. The spiritual nature of man: a study of contemporary religious experience) is a British student of this subject. His book outlines the results of interviews with thousands of people. He and his colleagues were interested in reviewing the results of these interviews to find patterns in which the spiritual aspect of the human being might be seen. “It seems to me that the main characteristics of man’s religious and spiritual experiences are shown in his feelings for a transcendental reality which frequently manifest themselves in early childhood; a feeling that ‘Something Other’ than the self can actually be sensed…” (p. 131).

Hardy found spiritual experiences to be very common, and catalogued and counted their variations. The most common sort of experience was a “sense of security, protection, peace” (on average, 253 mentions per 1000 accounts), followed by “sense of joy, happiness, well‑being” (212), “sense of presence (not human)” (202.3), “sense of certainty, clarity, enlightenment” (194.7), visions (181.3), and on through a total of 47 categories. Hardy also looked at circumstances which triggered these experiences. “Natural beauty” was one of a group of 4 such triggers that by far dominated the 21 types he listed (the other 3 main ones were “depression, despair;” “prayer, meditation;” and “participation in religious worship”). I’ll come back to the significance of beauty, later.

Another student of this topic was Abraham Maslow (1964. Religions, values, and peak experiences). Maslow was determined to remain within the confines of what he regarded as proper science: “I want to demonstrate that spiritual values have naturalistic meaning, that they…do not need supernatural concepts to validate them, that they…are the general responsibility of all mankind” (p. 4). Like Hardy, Maslow focused on the spiritual experiences of individuals. He concluded that all people have such experiences, whether the person is religious or not. The logical dancing Maslow did to avoid the taint of “supernatural” concepts is rather comical, in my view, but on the whole I think he succeeded in making the point that spiritual questions are important, that they are universal, and furthermore that they are the business of public education. Of course, Maslow was careful when defining “spiritual questions.” He was willing to acknowledge spiritual feelings and experiences, but chose to explain them in objective, physical terms. Nevertheless we find him pointing out, for example, that a typical characteristic of peak experiences is “that the whole universe is perceived as an integrated and unified whole…and that one has his place in it” (p. 59).

Literature Review: Tree Leaf Structure

by Carl Strang

A growing trend in the scientific world is on-line journals. Up until now, all the prestige among scientists has been connected with publishing in print journals. More than that, there is a prestige hierarchy of journals, with Science and Nature at the top, one or two leading journals in each discipline next, and so on. There is limited space in print journals, and a long lag time before a paper will appear in print. That is because each paper is submitted to a peer review, after which it will be accepted or rejected, and then it will take its place in the queue for upcoming issues of the journal.

Recent years have seen the emergence of a new group of peer-reviewed journals in on-line format. Some of these already have significant prestige associated with them. One in particular that I have begun to follow is PloS ONE. That first word actually is an acronym for Public Library of Science. It is a publicly accessible free website with a number of divisions by discipline.

Today I want to review a paper from that journal published last year.

Royer, D.L., et al. 2009. Phenotypic Plasticity of Leaf Shape along a Temperature Gradient in Acer rubrum. PLoS ONE 4(10): e7653. doi:10.1371/journal.pone.0007653

Leaves of different trees vary in shape and size. Some are relatively simple, like the aspen leaf in the photo above. Others, these maple leaves for instance, have lobes.

Evolution has in some cases pushed lobing to the point where the lobes become separate, as in the compound leaves of poison ivy.

Some leaves have toothed edges, again the aspen leaf is an example, while others have smooth edges as in these amur honeysuckle leaves.

Tropical trees are intriguing because their leaves are so similar, being simple and smooth edged to the point where you have no hope of distinguishing species by their leaf shape. So, this is the background for the study by Royer et al.

They looked at northern and southern strains of red maples, planting genetically known varieties of both strains in both Florida and in Rhode Island, and comparing degree of lobe cutting and of tooth number. Northern plants had more teeth and greater dissection, with genetic differences among strains accounting for 69-87% of the variation. Developmental response to differences in climate accounted for 6-19% of the variation. These contrasts are typical for northern versus southern plant species generally, and are thought to result from plants in the shorter northern growing season needing faster growth and nutrient delivery via sap flow. Leaves with more teeth and, to some extent, more lobes, tend to have more veins. More veins, teeth and lobes provide for more transpiration (evaporative water loss through the tiny gated stomata of the leaves) and guttation (production of droplets of water at the tips of teeth which, through evaporation, may draw more sap flow). Together these traits draw up sap more rapidly in the northern leaves, allowing their trees to achieve the more rapid growth they need.

Two Winter Marsh Plants

by Carl Strang

Today I want to compare winter and summer views of two plants that are common around Mayslake Forest Preserve’s stream corridor marsh. The first is one that I did not include in last summer’s phenological review because I could not get a satisfactory photo. Here is the best I could do then.

Here it is in winter.

The winter view does a better job of bringing out the plant’s distinctive structure. The other species bloomed prolifically around the fringes of the marsh last year: bur marigold.

This plant is in the beggar’s-tick genus Bidens. If you brush against members of this species when they are fruiting you will find bunches of seeds sticking to your clothing. Here are some bur marigolds in winter, still bearing some seeds.

Avoiding such annoyances certainly is one reason for learning to recognize plants when they are not blooming.

Winter Campfire 14

by Carl Strang

Winter is a time when we slow down and become introspective. Sitting and staring into the fire, we ponder the big questions. If you have been following this blog, you know that the focus here is science, science that can be done simply in outdoor settings. But we are more than scientists, and science has well defined limitations that need to be understood by everyone who does science or studies its findings. This winter I am using one post per week to develop my own viewpoint and biases, in particular sharing my take on the relationship between science and spirituality. In part this defines for me what these two realms of human experience are all about, and also develops the separate methods used for inquiry in each realm. I plan to place this paragraph in front of each entry in this series, so that those who are interested only in natural history or in scientific practice can skip these posts.

Barbour and Non-Time

One of the more radical physical theories I have encountered is the idea of British physicist Julian Barbour (1999. The End of Time). Barbour suggests that the Universe is composed of separate, static Nows (motionless configurations of the things of the Universe; he likens them to a deck of cards). Time doesn’t exist, just these Nows, some of which connect to form eternal sequences, on the basis of their similarity to one another, in particular the degree to which they contain records of one another. Barbour and Einstein share the concern that we only experience one moment at a time. This seems too limited a perception if we really live in the block-space-time universe suggested by relativity. Barbour points to problems with the block-space-time concept, and offers his own solution, but his framework also has many problems, for instance its dependence on parsimony. He admits, though, that in some ways block-space-time is close to his model.

Barbour’s theory seems to deny any true connection, such as Spirit, between Nows. I wonder if a spiritual dimension, perpendicular to all those of the physical universe, might allow such a connection. Our experience of the instants of time, and the decisions we make in them, would allow us to be co-creators of the whole. The importance of Story, and of being here now, i.e. of living in the present moment, are strong connections between Barbour’s model and the ideas I am developing in this series. Here is a relevant quote from his p. 329: “Why do we need time machines if our very existence is a kind of being present everywhere in what can be? … We are all part of one another, and we are each just the totality of things seen from our own viewpoint.” This is reminiscent of holographic models.

Time is a central paradox in both scientific and spiritual inquiry. I buy the contention of theoretical physicists that our everyday experience of time does not represent reality very well. In my view, fully accepting Eternity (whether in the form of block-space-time, Barbour’s deck of cards, or some other solution) is something that scientists in all other fields, and students of spiritual inquiry, should keep always in mind.

Mayslake Forest Preserve Overview

by Carl Strang

One of my studies is an ongoing natural history survey of Mayslake Forest Preserve in Oak Brook. That is where my office is located, so I can get out on the preserve on a regular basis. While I have mentioned various landmarks and places, I never have provided a geographic overview of the preserve.

Photo courtesy Forest Preserve District of DuPage County

Beginning at the preserve’s northwest corner, near the 31st Street (Oak Brook Road) entrance, here is a view of the parking lot marsh.

Just south of that marsh is the preserve’s oldest restoration project, the prairie.

Another prairie is developing around the stream corridor marsh.

Here is a view of the mansion from across Trinity Lake.

Trinity Lake drains into the preserve’s other lake, May’s Lake.

The north savanna embraces the north and east sides of May’s Lake.

Here is another view of the north savanna, looking south across the meadow.

The south savanna, between May’s Lake and the old friary building, had its brush cleared out a year ago.

The preserve is one of the smaller ones at 90 acres, but as you can see it has good habitat diversity.

Literature Review: Coyote Home Range

by Carl Strang

Here’s another paper I ran across in the Journal of Mammalogy for 2009:

Gehrt, Stanley D., Chris Anchor, and Lynsey A. White. 2009. Home range and landscape use of coyotes in a metropolitan landscape: conflict or coexistence? J. Mammal. 90:1045-1057.

Stan Gehrt has been conducting studies of carnivores in northeast Illinois for many years. The study area for this investigation included the north half of DuPage County and extended north into McHenry County. Gehrt and colleagues distinguished “transient coyotes” from “resident coyotes” after finding that some had very large home ranges (averaging 26.80 km2) while others’ were much smaller (average 4.95 km2). Resident home ranges were constant through the year, and did not vary with age or gender. Most coyotes included natural habitat in their home ranges, but a few had none. They “typically avoided land-use types associated with human activity (i.e., Residential, Urban Grass, and Urban Land)…Few coyotes were nuisances, and conflicts occurred when coyotes were sick or exposed to wildlife feeding by humans.”

This last comment underlines one of the two cautions we emphasize in my day job at the Forest Preserve District of DuPage County: don’t feed them, deliberately or inadvertently, and don’t leave pets (particularly cats and small dogs) unattended, even in a fenced yard. Coyotes are essentially everywhere in the suburbs, but most of the time are so good at staying out of sight that people are unaware they are around.

At 5 square kilometers per home range, 333 square miles in DuPage County and 2.59 square kilometers per square mile, a rough estimate of the permanent coyote population can be calculated:172 home ranges. If the home ranges are treated as territories, with a pair per territory, the number of coyotes is 344. That is a maximum, as much of the county’s area is composed of those land uses coyotes avoid, and it does not take into account pups or transient individuals, but does give a rough idea of the scale of the population. At around 1 coyote per square mile we are not exactly swarming with them.

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