Mayslake Animal Update

by Carl Strang

Every season contains the seeds of the next, and this was very true at Mayslake Forest Preserve last week. The migration season is well under way, though mainly it still features species that wintered in the southern U.S. rather than the tropics.

This winter wren was a classic example. Its kind invented skulking, but this one came out for a few seconds into plain sight.

This winter wren was a classic example. Its kind invented skulking, but this one came out for a few seconds into plain sight.

This male yellow-rumped warbler, in contrast, was not hiding. The challenge with him was that he seldom held still for more than a second. There was always another insect to chase.

This male yellow-rumped warbler, in contrast, was not hiding. The challenge with him was that he seldom held still for more than a second. There was always another insect to chase.

The wren and the warbler both nest well to the north, and will be with us only a short time.

Home hunting was another theme. The first bumblebee queen I saw this year was a Bombus bimaculatus.

She didn’t hold still, and didn’t stick around for long, but the yellow center of the second abdominal segment is visible in this blurry photo.

She didn’t hold still, and didn’t stick around for long, but the yellow center of the second abdominal segment is visible in this blurry photo.

Bumblebee queens in spring are probing for holes in the ground where they can start their colonies. Some animals make their own holes, and I found what may be a test dig by Mayslake’s pair of coyotes.

It was in an elevated site, and the hole was a foot in diameter, but not yet completely excavated. I’ll check on it occasionally. Coyotes only use dens to shelter their young.

It was in an elevated site, and the hole was a foot in diameter, but not yet completely excavated. I’ll check on it occasionally. Coyotes only use dens to shelter their young.

The abundance of the growing season still is in the future for most, however.

This fox squirrel was making do with some dried rose hips from the bush outside my office window.

This fox squirrel was making do with some dried rose hips from the bush outside my office window.

Clearly we are in a season of promise and preparation.

Another Year’s Squirrel Data

by Carl Strang

At the end of March I completed my third year of collecting data on habitat preferences of fox and gray squirrels at Mayslake Forest Preserve. The basic question is whether the usual preference of fox squirrels for savanna habitat and gray squirrels for forest will hold in an area where the savanna is high quality and the forest is low quality.

Fox squirrel

Over the first two years it was clear that both species preferred the savanna, but that preference has been stronger in the fox squirrel. This year the results were a little different. The area involved, 54.6 acres altogether, is 64% savanna and 36% forest. In the first year, 82% of fox squirrel observations were in savanna, 90% in the second year and 92% in this year just ended. The corresponding numbers for gray squirrels were 73%, 79% and 65%. That last number was perhaps the most remarkable, gray squirrels in the past year appearing in the exact proportions of the two habitat types on the preserve.

Gray squirrel

That is the only number in this entire study that shows no statistically significant difference from expected values (actually, the chi-squared test statistic is calculated from the numbers of observations rather than the percentage values; this year I had 157 observations of fox squirrels, 75 of gray squirrels). I continue to gather these data each year because the preserve continues to change, thanks to the efforts of the restoration team. High quality savanna is improving, and low quality forest is being cut back.

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.)

Fox Squirrel Dossier

by Carl Strang

This week’s species dossier is one of my larger ones.

Fox Squirrel

Fox squirrels are distinguished from our other common tree squirrel, the gray squirrel, by the reddish tones in the tail and belly.

This is a squirrel of woodlands and residential areas with trees. The fox squirrel is the only large tree squirrel of the Culver, Indiana, area. They nest in tree cavities or in leaf nests; some used leaf nests all winter at Willowbrook Forest Preserve, Illinois. Nest building involves cutting of leafy branch-ends. A leaf nest in cross section is made of those leafy twigs, woven into a framework of thicker sticks, with a fresh leafy lining. Overall it has a very thick wall with small insulated cavity within.

Squirrel nests are approximately the diameter of a basketball.

Fox squirrels feed on the ground and in trees. They begin to eat acorns and hickory nuts in August when those still are green. Hickory nuts and acorns are consumed in treetops, especially early in morning and late in afternoon, resulting in a distinctive rain of fragments as hulls are gnawed away. Squirrels (gray squirrels?) also ate black gum fruits in Pennsylvania on Reineman Sanctuary in late fall. Generally they open large nuts (hickory, walnuts) neatly, prying them open on the seams.

Fox squirrel with a pair of shagbark hickory nuts.

They also bury individual acorns, nuts, black cherry pits, etc., in the fall. Distinctive burying site goes into earth at a 45 degree angle or a little shallower, producing an oval shaped bare soil excavation site about 1×2 inches (wider than tall) in soft soil, smaller in hard soil. Mushrooms also are on the fall food list near Culver. Diet in early winter emphasizes excavated nuts buried earlier.

Squirrel tracks, right, follow a winding course as the animal sniffed for a buried nut. On the left is the hole where it excavated one.

Twigs and bark, e.g. of elm, eaten occasionally in mid- and late winter. Buds, e.g. of maple, are added as those expand in spring. Developing elm seeds are heavily consumed in May in DuPage County, generally twigs are cut and seeds eaten from them. Occasionally they gnaw bones.

Fox squirrel eating buds in spring.

Fox squirrels have two breeding seasons, typically, in spring and fall, with 2-5 young per litter. Young began to appear at the Willowbrook Wildlife Center hospital in mid-March (born mid-late February) and mid-August (born late July or early August). Young normally begin to emerge from the nest in May or late September. Young play in vigorous chasing and hiding games on tree trunks and in branches, occasionally extended onto the ground. Adults sometimes play as well, also tease dogs. Leap between trees. They use suspended wires as tightropes between trees and over roads.

These could be fox or gray squirrel footprints.

Tree squirrel tracks are distinctive, the 5-toed hind footprints about 1.25 inches long, with 3 parallel middle toes close together, pointing forward, and outer toes pointing out at angles. The 4-toed front footprints show more spread and independence of toes. The traveling gait typically is a gallop, with front feet leaving ground before back feet land. The back feet are side by side, as are the front feet. Slowing down causes front feet to get closer and closer to back footprints, until one or both front footprints are in front of the back feet. Acceleration also begins with a set of footprints showing the bound gait. Squirrels sniffing slowly over the ground sometimes use the diagonal walk. Fox squirrels show considerable ingenuity and acrobatic ability in overcoming bird feeder protections.

Early spring 1986, Taft Campus of Northern Illinois University, north central IL, with snow still on ground. A fox squirrel, opportunistically foraging in a temporary meltwater stream, looked much healthier than the many gray squirrels fastidiously foraging on the wet-snow-covered hillside nearby.

24NO86. Squirrel began to go onto a branch with 2 great horned owls. The squirrel stopped, tail twitching, sat still for a while, then backed and started to go on a branch over the owls’ heads. They were watching it. Finally it turned around and ran down the tree.

12DE86. Puffer Lake, Morton Arboretum, IL. Fox or gray squirrel tracks in snow that fell yesterday afternoon, on ice among cattails at edge of lake. The tracks were made early this morning. Diagonal walk first 7 feet onto ice, then slow gallop gait.

Fox squirrel, winter.

14MR87. Fox squirrel eating cherry and elm buds at Maple Grove Forest Preserve.

30AP87. Fox squirrel feeding heavily, frenetically, on large green silver maple fruits (seeds only; dropping wings). Also on 1MY, 8:30 a.m. both days.

4MY87. Squirrel-cut elm twigs with fragments of seeds on ground.

6MY87. Early evening, a fox squirrel feeding in an elm top at Willowbrook. Mostly clipped twigs first, then stripped them of seeds, and finally dropped them. The squirrel removed more foliage in 3 minutes than a noctuid caterpillar would in its entire life.

18DE87. 4 days after an abrupt 1-foot snowfall, little but rabbit and squirrel tracks can be seen in the Willowbrook Back 40. The latter are relatively few, restricted to woods.

25MY88. A squirrel when being stealthy carries his tail behind him like the cloak on a figure in an old novel.

This one looks pregnant.

29MY88. Fox squirrel numbers at Hartz Lake (in Indiana) appear limited by hickories. The few squirrels I’ve seen to date have been in parts of woods where hickories are (may simply be a preference, if hunters are keeping numbers low).

20SE88. A fox squirrel nest came into Willowbrook from Lombard with 3 young. The nest was made of leafy elm twigs, with grasses and a work glove toward the center. Overall shape was like an urn, with branches interwoven to nearly cover the entrance. Couldn’t tell for sure whether the entrance was on top or side. Nest blown out of tree by storm.

27JL89. Fox squirrel still feeding heavily on red half-ripe mulberries at Willowbrook after purple ripe ones have been available more than 1 month.

10MR90. Warrenville Grove Forest Preserve. Fox squirrel lunges up tree when climbing, pushing with all four feet at once. Toes catch in cracks, don’t appear to slip although a slight adjustment with a foot may be made now and then before the next lunge.

24JL90. Fox squirrel still eating mulberries.

15NO90. Willowbrook. A fox squirrel eating catalpa seeds right out of the pod, and letting the wings fall.

13JA92. Fox squirrel eating box elder buds, Willowbrook.

22AP95. Midafternoon, Warrenville Grove Forest Preserve. 2 fox squirrels feeding heavily on American elm buds in a 6″dbh tree.

13OC96. 3 fox squirrels in full bark, simultaneously, in Mom and Dad’s Culver front yard. A large cat was their target. They were turned so their bodies pointed in its direction and they were focused, looking straight at the cat.

Not a hibernator, the fox squirrel remains active all winter.

19FE99. Fox squirrel eating expanding silver maple buds, Willowbrook.

4MR99. At mid-day a gray squirrel emerged from a hole in a large, dead willow at Willowbrook to drive away an approaching fox squirrel. The gray immediately returned to the hole.

20AP99. Fox squirrel feeding on buds or expanding leaves of a black cherry tree with leaves much more expanded than those of other cherries at Willowbrook.

28AP99. Willowbrook. Fox squirrel eating silver maple seeds.

13OC99. Willowbrook. Young fox squirrel out of nest. Another fox squirrel eating box elder seeds.

21OC99. Willowbrook. Several fox squirrels gathering walnuts.

Synchronized acorn-eating team, Mayslake savanna.

27OC99. Fox and gray squirrels both are active. The former have been eating nuts in recent days, one this morning in a box elder eating seeds, another appearing to work on a broken down old nest.

28OC99. Gray squirrel with nut, fox squirrel eating box elder seeds.

1NO99. Willowbrook again. Fox squirrel eating box elder seeds.

17NO99. A gray squirrel (young) and a fox squirrel both eating box elder seeds at Willowbrook.

2DE99. Several gray squirrels and 1 fox squirrel foraging on the ground.

30DE99. Fox squirrel at Willowbrook building leaf nest 15 feet up in a buckthorn in a tall-brush area. Taking leaves from nearby small oak that had not dropped many of them.

2FE00. A fox squirrel carried a ball of snow up onto a branch and ate from it.

14FE00. Many gray and fox squirrels this winter in nests only 12‑14 inches outer diameter at Willowbrook.

25FE00. Willowbrook, afternoon. 2 fox squirrels eating buds from a mulberry tree rich in witches’ brooms. Temperature 70F.

2MR00. Willowbrook. 2 fox squirrels sharing a hole in the trunk of a large willow, 1 of them adding leaves picked up from the ground.

Grooming the fur.

4MR00. A gray and 2 fox squirrels feeding on the expanding buds of an American elm near the Joy Path of Morton Arboretum. As I left the path to approach the tree to identify it, the gray squirrel immediately left and ran to other trees. As I walked up to the trunk, the lower of the fox squirrels finally left, but the higher one remained.

15MR00. Willowbrook. Fox squirrel nest high in the very top of a red oak across the exhibit trail from the eagle cage (occupant barked at another fox squirrel lower in tree). A fox squirrel eating expanding sugar maple buds.

13AP00. A fox squirrel feeding on expanding sugar maple buds, Willowbrook.

19AP00. Willowbrook. 2 fox squirrels eating expanding sugar maple buds.

7MY00. West DuPage Woods F.P. 2 fox squirrels clipping American elm twig ends and eating the nearly ripened seeds, then dropping the twigs with leaves.

1JA02. A fox squirrel at the Arboretum eating honey locust seeds from a thornless tree on a very cold day. Sometimes it ate individual seeds from the pod attached to the tree, sometimes removed entire pods and took the seeds from them.

This fox squirrel was mobbed by a pair of Baltimore Orioles in June of 2009 until it left their nest tree.

5OC10. Mayslake. A fox squirrel chased a gray squirrel on the ground in the south savanna.

27JA11. Mayslake. Fox squirrels feeding in thornless honey locust in south (former) friary grounds, presumably getting seeds from pods.

1DE11. Fox squirrel eating honey locust seeds from pod on ground.

Worth the Effort?

by Carl Strang

On Saturday I went to Les Arends Forest Preserve in Kane County to watch a high school regional cross country meet.

The boys’ race, half a mile in.

While waiting between the girls’ and boys’ races, I sat and had lunch at a beautiful wooded edge.

Something caught my eye.

In the top of a spindly sapling 15 feet or so tall, there was a lump.

See it, near the top?

It proved to be a walnut, wedged in a fork of branches.

The sapling was not the source of the nut.

A walnut is a good bundle of calories for a tree squirrel, and one such rodent (probably a fox squirrel) had gone to the effort to grab a nut, husk and all, haul it out into the secondary growth perhaps 20 yards from the source tree, and carry it to the top of the sapling, wedging it well enough that recent storms have not dislodged it. Now, if that squirrel can just remember that the nut is there, and is not pre-empted by another sharp-eyed bushytail, the effort will have been worthwhile.

Another Mystery Death

by Carl Strang

Perhaps the question has occurred to you: moving through a wild landscape you see so many animals and signs of their activity. You know they all die, sooner or later. Why do we so seldom see the bodies? Part of the answer, I think, is that some animals die in hidden places, knowing they are vulnerable from illness or injury and wanting to avoid predators. Others are killed by predators and consumed. Scavengers can make quick work of corpses. Still, if you spend enough time in the out-of-doors, especially off trail, you will find bodies. Here is a recent example from Mayslake Forest Preserve.

This fox squirrel was beneath an oak in the north savanna. If I had stuck to the trails I never would have found it.

There was no sign of violence that I could see. I noticed fur missing from the squirrel’s belly.

One possibility was mange, or another hair-loss illness.

When I rolled the body with a stick, I saw that this was a mother squirrel. The hair was a normal loss around the nipples. Sadly, this implied that there were baby squirrels in a nest whose survival was unlikely, though this was near the time of weaning. There is a story here, but I don’t have the skill to discern more of it.

Another Year’s Squirrel Data

by Carl Strang

Fox and gray squirrels are familiar animals in northeast Illinois. They are easy to tell apart. Gray squirrels have pale gray belly fur, and their tails are mainly gray toned.

Gray squirrels also are smaller than fox squirrels.

Fox squirrels have reddish brown fur beneath, and their tails are reddish and black.

The orange pigment also occurs in a fox squirrel’s bones, and the lenses of its eyes. Fox squirrels have built-in sunglasses.

As I mentioned a year ago, fox and gray squirrels are adapted to different habitats. Gray squirrels are forest animals, while fox squirrels live in the more open savannas. Both species occur at Mayslake Forest Preserve, where the savannas are high in quality but the forests are poor. By “poor” I mean they have lots of buckthorn, very little diversity of herbaceous plants, and the trees are mainly young members of weedy (fast-growing, relatively short lived) species.

I have been keeping records of where I see fox and gray squirrels at Mayslake. As there is more savanna than forest habitat there, I expect to see more fox squirrels. To what extent do the two squirrel species stick to their expected habitats? Here are the results of two years’ study. Observations total 853 for fox squirrels, 209 for gray squirrels. As expected, the former species appears to be much more abundant.

If the two species had no preference, i.e. occurred in forest and savanna areas in proportion to those areas’ sizes, I would expect 528 of the 853 fox squirrel observations to be in savanna, 325 in forest. Instead the numbers are 726 and 127, respectively. This shows the expected strong preference for savanna (for what it’s worth, the χ 2 test statistic value is a whopping 194.8).

If gray squirrels were showing no habitat preference, I would expect 129 observations in savanna, 80 in forest. The observed numbers were 160 and 49, respectively. This likewise reveals a preference for the superior savanna habitat (chi-squared = 19.5, also plenty large).

The preference for savanna does not appear to be quite so strong in the gray squirrel, however. Is there a difference between the species? If I base my expectations for gray squirrels on the ratios seen in fox squirrels, I should have seen 178 gray squirrels in savanna, 31 in forest. Again, the observed numbers were 160 and 49. Here the χ 2 = 12.3, large enough to support a difference between the species’ degree of preference. I will continue to monitor these two species, to see if there are any changes over the years.

Baltimore Oriole Dossier

by Carl Strang

It’s time to share another of my species dossiers. This one brings together my experiences with a bird that at the moment is to be found in the tropics. Spring can’t come too soon.

Male Baltimore oriole.

Oriole, Baltimore

This bird’s song is very loud, composed of clearly defined, sharp notes, usually a bundle of several with mixed pitches. The Baltimore oriole stays near treetops in feeding, generally. They nest in residential neighborhoods and open woods, especially beside ponds, lakes and rivers. The nest is a distinctive, unusual hanging basket, usually attached to an exposed, slender branch tip over water or a road. One spring I watched part of a nest-building, the female bringing long fibers and weaving them into a bag that already had its basic form. The stroking, pulling bill movements of the bird used the new fiber to fill a space and strengthen the bag.

Even as it deteriorates in winter, a Baltimore oriole nest is a beautiful object.

3JE86. A male foraged low in a crabapple, moving fairly quickly between perches, moving 2-3 feet at a time, looking among leaves, often burying his head among them and searching. Once he dropped to the ground in pursuit of a prey that jumped to evade him.

14JE87. Adult eating mulberries at Culver fish hatchery.

7MY88. Singing at Culver.

4MY99. First migrant noted at Willowbrook. Last spring migrant observed there 27MY.

11AU99. First fall migrant noted at Willowbrook. Last one noted 24AU.

This nest is relatively visible.

17JE00. Arboretum, Joy Path. Adult male foraging in the branch tips of a bur oak where leaves are clustered. It was searching and probing into clumps of dead leaves. It caught an adult moth, removed the wings, then flew straight to its nest overhanging the path at least 20 feet up. The moth was fairly large and heavy bodied, perhaps a noctuid. The nest is within a clump of leaves so that it does not appear suspended. Later, both the male and female were carrying food to the nest. When they were there, and for a few seconds after they left, a chorus of faint peepings was audible.

2JE01. Meacham Grove, east part. A female oriole led me to a nest that was so woven into the cluster of leaves at the end of a bunch of slender twigs that the nest was practically invisible.

There is a Baltimore oriole nest here, but it is well buried among the leaves.

16JE01. Newly fledged orioles still were close to the nest at the Arboretum, Heritage Trail. The nest was above a service road-trail just inside the fence separating the savanna area from Hidden Lake Forest Preserve, on the end of a descending oak branch’s lowest twigs. One of the fledglings was still perched just above the nest, the others were scattered on that branch and in nearby branches of other trees. They were essentially motionless for a long time, but very vocal, with distinctive calls: 3 quick identical notes that sounded like uninflected robin notes.

31AU02. A Baltimore oriole in full male breeding plumage, singing at Lincoln Marsh from the very top of a tall tree. Not full volume, and only little chattering phrases, but clear oriole voice tones, whistles. Sang for several minutes.

27JE08. Baltimore oriole fledglings have a call that is a rapid series of clear notes rising as on a scale.

2MY09. An oriole at Fullersburg was taking nectar from buckeye flowers.

4MY09. Mayslake. Series of photos of an oriole probing clusters of oak flowers and opening leaves.

Foraging oriole at Mayslake.

1JE09. Mayslake. Pair of Baltimore orioles mobbing a fox squirrel in the medium-sized cottonwood closest to the SE corner of May’s Lake. They gave frequent, loud, identical, slightly slurring notes but did not attack the squirrel. I found the nest at the end of the lowest branch on the east side of the tree, 15-20 feet up. The squirrel eventually jumped to another tree without finding the nest, escorted by the male oriole, and the female almost immediately returned to the nest.

Here is the female giving her alarm calls.

10JE09. The same pair of the previous entry is feeding a cowbird fledgling just outside their nest. In the brief time I watched, the female fed the cowbird once, the male fed it once and a nestling once.

Cowbirds and orioles are in the blackbird family.

Apparently this episode of nest parasitism doomed the orioles’ own young, as I never saw any oriole fledglings from that nest.

Literature Review: Short Term Genetic Change

by Carl Strang

Today I will attempt to tie together four different studies published last year that focused on a wide range of different organisms but had in common the theme of rapid genetic change, casting a new light on evolutionary processes. We’ll begin with fox squirrels.

Fox squirrels are revealed to have changed rapidly in postglacial times.

This first study (Moncrief, Nancy D., Justin B. Lack, and Ronald A. Van Den Bussche. 2010. Eastern fox squirrel (Sciurus niger) lacks phylogeographic structure: recent range expansion and phenotypic differentiation. J. Mammal. 91:1112-1123) looked at the divergent populations of fox squirrels across eastern North America. Body size and coat color variation across 10 subspecies groups had been associated with a model of expansion from separate glacial refugia in Florida and Texas. In other words, once the glacier melted away, woodlands expanded northward and the squirrels went with them. Populations north of Texas were expected to have connected to those that survived the thousands of years of glaciation in Texas, with a similar connection between more eastern populations and a Florida refuge. Study of the genetics of these populations showed no such connections, however. The data suggest a rapid postglacial expansion, with the observed differences in size and coat color evolving in place, indicating “rapid morphological divergence within the past 14,000 years.”

Millenium Park, Chicago. How does a forest ant make it in the big city?

Now we get out the magnifying glass and look at a smaller creature (Grzegorz Buczkowski. Extreme life history plasticity and the evolution of invasive characteristics in a native ant. Biological Invasions, 2010; DOI: 10.1007/s10530-010-9727-6. As described in a ScienceDaily article). The odorous house ant is a native forest species, in its original configuration with a colony of a single queen and around 50 workers, living in an acorn shell or other small space. In urban areas they expand to supercolonies with as many as 6 million workers and 50,000 queens. They are one of the most common house ants, named for a cocoanut or rum odor when crushed. Buczkowski, a researcher out of Purdue University, has found an intermediate state in urban parks, with 500 workers and a single queen. Other species have not made this kind of transition, which is ecologically extreme, from a K-selected life history strategy (focused on persisting in a narrowly defined competitive situation, with the production of few, well-equipped offspring) to an r-selected life history strategy (focused on high reproductive output, wide dispersal, and high mortality of less well provisioned offspring).

The next study focused on butterflies in the western mountains.

Sticking with insects, we look next at the process by which one species evolves into two (McBride CS, Singer MC (2010) Field Studies Reveal Strong Postmating Isolation between Ecologically Divergent Butterfly Populations. PLoS Biol 8(10): e1000529. doi:10.1371/journal.pbio.1000529). They looked at populations of the Edith’s checkerspot butterfly Euphydryas editha on western mountain slopes. Caterpillars of different populations develop on different plants, some on Collinsia torreyi (blue-eyed Mary) and others on Pedicularis semibarbata (pine lousewort). The plants grow together, but at any given spot the caterpillars are found on only one of them. When brought together in the lab the butterflies hybridize, but experiments demonstrated that the hybrid offspring are at a strong disadvantage. Collinsia-feeding populations lay small clutches of eggs near the tops of the plants, Pedicularis feeders lay larger clutches near the bottoms. Hybrids are intermediate, and so have poor survival. They miss the fresh leaves of each species, and they either overwhelm the Collinsia food source or are inadequate to match egg mortality on Pedicularis. This study is significant in providing a clear example of incipient speciation in which the process of extrinsic postzygotic isolation is important. “Extrinsic” means that the hybrid offspring are themselves fully healthy and functional, but external environmental factors work against them. “Postzygotic” is a reference to the fact that the different varieties of the butterfly are willing and able to mate with one another, but selection acts on the offspring.

All of the above studies are given some context by the final one I include today (Stephan Ossowski, Korbinian Schneeberger, José Ingnacio Lucas-Lledó, et al. 2010. The rate and molecular spectrum of spontaneous mutations in Arabidopsis thaliana. Science 327:92-97). They directly measured the number of mutations appearing in genomes of this plant species (mouse-ear cress) over 30 generations. The results, if translated to human genetics, would represent 60 DNA base pairs in an average individual that are mutated to be different from those of the parents. This is a larger quantity than anyone would have expected, and it has the highly significant meaning that in a large population, genetic material could change rapidly, allowing for significant genetic flexibility on which natural selection can work. “’Everything that is genetically possible is being tested in a very short period,’ adds Lynch [a co-author, interviewed in a ScienceDaily article about the study], emphasizing a very different view than perhaps the one we are all most familiar with: that evolution reveals itself only after thousands, if not millions of years.” Squirrels, ants and butterflies appear to show that this result is not limited to plants.

Digging Squirrels

by Carl Strang

Tracking is a valuable way to learn about wildlife. So is familiarity with the scientific literature. Today we combine the two, benefiting from both. The recent first snowfalls of the season have made clear the extent to which tree squirrels are digging up their buried food. In northeastern Illinois we are talking about both fox squirrels

Fox squirrel. Note the red belly and tail color.

and gray squirrels.

Gray squirrel. Here the tail is edged in white; the belly likewise is pale.

In my walks around Mayslake Forest Preserve over the past couple of weeks it is clear that squirrels have been digging like crazy, excavating previously buried acorns and nuts.

Squirrel excavation site. Note how the squirrel sniffed around for a while to the right before zeroing in on the buried food. An earlier study, the reference to which I am too lazy to dig out at the moment, found that squirrels remember only the general areas in which they have buried food. They find the precise spot with their sensitive noses.

Doesn’t it seem awfully soon to be digging out food that was buried only a few weeks ago? This is where the literature familiarity helps. Last year I described a study of the discriminatory behavior of tree squirrels.

It turns out that these squirrel guys and gals are fattening in the fall on the lower quality acorns and nuts. They bury the better ones. By now these foods have all been eaten, stored, or have germinated and thus rendered unavailable as food. So it makes sense immediately to return to the stores and begin exploiting them.

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