Mayslake Birds

by Carl Strang

Bird action at Mayslake Forest Preserve has sped up to the point of being hard to follow. Migrants have been stopping by in good numbers.

Baltimore orioles are scattered through all the woodlands. Some will stay and nest.

Baltimore orioles are scattered through all the woodlands. Some will stay and nest.

Warbling vireos are another recent arrival.

Warbling vireos are another recent arrival.

Savannah sparrows haven’t nested at Mayslake yet, but one day last week the meadows and prairies were full of them.

Savannah sparrows haven’t nested at Mayslake yet, but one day last week the meadows and prairies were full of them.

I know this is a broken-record theme for me (for those of you old enough to know what that expression means), but note how in the face-on view all those head stripes converge on the bill, accentuating it for rival intimidation (maybe). I’m reminded of Maori facial tattoos.

I know this is a broken-record theme for me (for those of you old enough to know what that expression means), but note how in the face-on view all those head stripes converge on the bill, accentuating it for rival intimidation (maybe). I’m reminded of Maori facial tattoos.

This Canada goose brood appeared on Mays’ Lake.

This Canada goose brood appeared on Mays’ Lake.

On the same day, the nest in the nearby stream corridor marsh was empty, with open eggshells, almost certainly that brood’s origin.

On the same day, the nest in the nearby stream corridor marsh was empty, with open eggshells, almost certainly that brood’s origin.

The other nest, in the parking lot marsh, has been abandoned. Three unhatched eggs are visible. The highest water levels in recent rains may have reached their undersides.

The Cooper’s hawk nest is under incubation just off the preserve in a neighbor’s yard.

The Cooper’s hawk nest is under incubation just off the preserve in a neighbor’s yard.

The nest was found by Vicky S., a former student of mine who went on to mentor with some of the area’s top birders and should be regarded as one of their number at this point. There’s some satisfaction to be had in being surpassed by one’s student. She pointed out that this is an unconventional structure, the hawks having added a layer of sticks to the top of a squirrel nest.

Bobber-Eating Tree

by Carl Strang

Winter reveals much that was hidden in the growing season. When the deciduous trees and shrubs have dropped their leaves, green walls are replaced by vistas. Smaller things now come into view as well, including a bobber-eating tree at the edge of Trinity Lake in Mayslake Forest Preserve.

How many red and white ball bobbers can you find?

How many red and white ball bobbers can you find?

I am reminded of the kite-eating tree of Charles Schultz’s Peanuts cartoons. This is right above a popular point on the lake shore for fishermen in summer. It is not entirely innocent, though, as those bobbers are attached to lengths of fishing line that are a potential entanglement hazard for birds. As I have previously documented here, orioles make use of some of the discarded line in their nest-building.

Mayslake Birds Update

by Carl Strang

We have entered the time when most birds are focused on raising young. It is much quieter at Mayslake Forest Preserve now that territories are established and the effort of feeding nestlings occupies the parents’ time and energy.

This Baltimore oriole’s nest hangs above the trail near the northeast corner of Mays’ Lake.

This Baltimore oriole’s nest hangs above the trail near the northeast corner of Mays’ Lake.

The nest is sufficiently concealed by black cherry leaves that its composition is difficult to read, but I would be surprised if it is not constructed largely of fishing line, as has been the case for all recent oriole nests there.

Red-winged blackbirds are ever-ready to cuss out any person who comes anywhere near their nests.

Red-winged blackbirds are ever-ready to cuss out any person who comes anywhere near their nests.

The preserve’s pair of eastern kingbirds is much quieter than they were before nesting.

The preserve’s pair of eastern kingbirds is much quieter than they were before nesting.

Some broods already have fledged.

Yesterday this tree swallow brood occupied a dead tree at the stream corridor marsh.

Yesterday this tree swallow brood occupied a dead tree at the stream corridor marsh.

A final, sad note was the find of a dead chimney swift in Mayslake Hall.

It’s not clear how the swift got inside, or how a bird that nests in dark chimneys could have met its end in a room as spacious as the Event Hall.

It’s not clear how the swift got inside, or how a bird that nests in dark chimneys could have met its end in a room as spacious as the Event Hall.

Swifts have stiff tail feathers, which they use to prop themselves against interior chimney walls.

Swifts have stiff tail feathers, which they use to prop themselves against interior chimney walls.

I took the swift to Willowbrook, which periodically delivers specimens to the bird department at the Field Museum of Natural History in Chicago.

Rose-breasted Grosbeak Species Dossier

by Carl Strang

As usual, the dossier begins with the paragraph that established the file in the mid-1980’s. In this case I didn’t have much to say because my experience with the species was limited. Since then, dated notes have appended observations that I felt added to my understanding of the species.

Grosbeak, Rose-breasted

This species was relatively rare around my home town of Culver, Indiana. My first were a pair in my neighborhood in the town. The male sang from high in trees or TV aerials. His song began with a phrase much like the theme of the “Guestward Ho” TV series which was current then. That mnemonic has helped me recognize it elsewhere in Indiana as well as Pennsylvania and Illinois. They also have a loud “pick” call distinctive in quality from their close relative the cardinal. Foraging movements are slow, taking their time while visually searching for insects at mid to high elevations in trees. They are uncommon during the breeding season (though abundant in migration) in DuPage County, with occasional single pairs here and there in savannah-like forests. They are especially common for a couple of weeks during migration in May.

Adult male rose-breasted grosbeak

Adult male rose-breasted grosbeak

5MY87. First song of the year heard at Willowbrook Forest Preserve.

25JL87. Hartz Lake, Indiana: An adult male fed 10-15 feet up in saplings. Deliberate: about 10 seconds per perch, looking apparently over a radius of several feet, moving 2-5 feet between perches.

A male reaches for a food item. They can look very parrot-like in this maneuver.

A male reaches for a food item. They can look very parrot-like in this maneuver.

13SE87. A female was in a mixed flock with a red-eyed vireo, a Tennessee warbler, and several catbirds and robins.

7MY88. First song of the year, Culver, Indiana.

11MY88. A female was in Willowbrook Forest Preserve.

8MY89. I saw grosbeaks today and on May 6th at Willowbrook.

Singing posture

Singing posture

4MY99. First migrant noted at Willowbrook. Last observed there 14MY.

26AU99. First migrant noted at Willowbrook. Last one noted 29SE.

4SE99. A grosbeak in female plumage at Willowbrook produced “pick!” notes and bits of low-volume warbling song.

11JE00. Rose-breasted grosbeaks were in a diverse forest near Langlade, Wisconsin, associated with the Wolf River riparian edge and with savanna-like areas where trees were more scattered. Deciduous trees were abundant in those areas. Other birds in those habitats were least flycatcher, Baltimore oriole and black-throated blue warbler.

23-4SE00. Grosbeaks were numerous along the Prairie Path just east of Industrial Drive and bordering the West Chicago Prairie, in the hedge-like edges.

21MY08. Fullersburg Woods. A rose-breasted grosbeak nest was on Willow Island, midway along the east side. It was 10 feet up in the top of a buckthorn, 15 feet in from the trail, female incubating. The nest structure resembles that of the cardinal but thinner so you can see through it in places.

Baltimore Oriole Nest Addendum

by Carl Strang

I ended Monday’s post by asking whether the heavy use of fishing line as nest material by a Baltimore oriole at Mayslake Forest Preserve was a peculiarity of the individual builder, or a consequence of the availability of material that any female might prefer. I have a tentative answer to that question. As leaves are falling from the trees, more nests are becoming visible. I was aware of a second Baltimore oriole nest by a different pair at the north edge of the savanna. A couple days ago I checked it out.

Despite being more than 50 meters from the lake, this nest likewise has much fishing line.

I know that this nest was made by a different female, as it was active at the same time as the one featured on Monday. I also found a third oriole nest from this season.

This was between the other two nests, and probably was a second nest of one of the two pairs. Again, much fishing line was used.

So it appears to be the material rather than the bird. These last nests concern me, as there is much line freely extended from them. Though birds probably will be able to stay clear, entanglement is a potential hazard.

Synthetic Oriole Nest

by Carl Strang

[Note: this post first appeared as a Nature Note in the Observe Your Preserve website]. Back on May 11 I watched a female Baltimore oriole as she attempted to collect some monofilament fishing line tangled in a shrub at the edge of May’s Lake in Mayslake Forest Preserve. After at least 5 minutes of effort she gave up and flew away. A couple weeks later, a member of a group I was guiding spotted an oriole flying to a nest in a large oak tree near that point on the lakeshore. Early last week I found that nest on the ground beneath the tree, apparently detached by one of our recent wind storms.

The odd color first drew my eye.

It soon became clear that the nest was composed largely of fishing line and other plastic fibers like those woven to form blue tarps. Perhaps inevitably, some of the line had a fish hook tied to the end.

Fortunately the hook was hanging from the outside of the nest, though it was close to the top edge.

This is a rare instance when leaving litter, in particular fishing line, had a harmless or perhaps helpful impact on the local wildlife. Most of the time such material is dangerous, posing an entanglement hazard that could result in death or serious injury to wild animals. That line is designed not to break easily. In time it may physically erode, but it will not decompose and it potentially puts wildlife at risk for years. The importance of picking up your litter cannot be overemphasized.

To this point the story was worth posting about, and I did so in the Nature Note at Observe Your Preserve last week. It turned out that there was an additional chapter to come, however. Later in the week, as I walked along the top of the savanna ridge not far from where I found that nest, I looked up and noticed that last year’s Baltimore oriole nest still is attached and largely intact.

This is the photo I took last week.

It proves to have much fishing line and at least one strand of a similar blue plastic weave. A comparison to the photo I made last December confirms that it is the same nest, and that there has been very little change, except that the supporting twigs have grown.

Some of the plastic fibers remain in exactly the same position after nearly a year.

This underlines the persistence of these plastic materials, and it raises other questions. Were the two nests woven by the same female, one with a preference for these synthetic fibers? The nests were, after all, built only a few trees apart from one another. Alternatively, would any oriole take advantage of the availability of such fibers?

Mayslake Avian Update

by Carl Strang

With the frantic migration season fading away, birds have entered the frantic breeding season. Indeed, some birds already are on their second brood.

I took this photo of a robin fledgling back on May 22, and saw some second nests under incubation last week.

Birds continue to wander, however, and unexpected individuals pop up from time to time.

This coot showed up on May’s Lake one day last week, for example.

There always is something new to learn. On Thursday of last week I saw a female orchard oriole in the north savanna. She seemed to be at home, and so I returned there on Friday, mixing plant survey work with a wish to gain more information on the orioles’ presence.

It didn’t take long to find the male.

He was fairly vocal, but his song and call were more similar to those of the Baltimore oriole than other orchard orioles I have observed in the past (though lacking the loudly whistled “hey batter batter batter” call of that baseball-oriented bird). I had no record of this species at Mayslake last year, but now I wonder if I was hearing this male and labeling him a Baltimore oriole. There always is something new to learn.

Species Dossier: Brown-headed Cowbird

by Carl Strang

Cowbirds haven’t arrived in our area yet this spring, but it won’t be too long. The following represents my limited knowledge of this, our main local nest parasite.

Cowbird, Brown-headed

Male brown-headed cowbird

This blackbird has been common essentially everywhere in the eastern U.S. I’ve gone. They feed in and around open areas and fields. Females lay eggs in other birds’ nests, early examples observed in warbler nests of a few species. They sometimes stayed around Culver, Indiana, in winter, taking seeds from feeders.

31MR99. First of season noted at Willowbrook.

29MR00. Willowbrook. Cowbird males displaying in high, bare tree tops: a group of 5, and a group of 3 (one of the latter had left the first group). No females were present with the group, but a female was present elsewhere on the preserve. The display consisted of fanning the wings out to the side, fanning the tail and lifting it above back level, then bowing or leaning forward to the point of sometimes losing balance. While performing the display, the bird at least sometimes gave its high‑pitched call. (I call this the falling-down-drunk display.)

Falling-down-drunk display, closely watched by a female.

1JL00. A female yellow warbler fed a cowbird fledgling near the south end of Silver Lake at Blackwell. Earlier this week a pair of scarlet tanagers fed a cowbird at Willowbrook, and half a dozen times this spring I have seen male cardinals feeding them (some were the same pair, but at least 3 different broods were involved), also at Willowbrook.

12OC02. After not seeing many in recent weeks, a couple individual cowbirds appeared earlier in the week at Willowbrook, and today, a number of them, especially young ones, were at Fermilab.

19JE08. A pair of gnatcatchers fed a cowbird fledgling at Fullersburg.

20JE09. Last year I also saw song sparrows feeding a cowbird at Fullersburg. This year at Mayslake I have seen cowbirds fledged by phoebes and Baltimore orioles.

Fledgling cowbird being fed by a female Baltimore oriole.

15JL09. Mayslake. Yesterday in the south savanna a cowbird fledgling was being attended by a song sparrow. Today another fledgling was in the north savanna being fed by a phoebe, clearly a different brood or pair than the earlier one (last observed 3 July).

The Only Oriole Nest

by Carl Strang

Compared to the previous two years at Mayslake Forest Preserve, 2011 seemed relatively depauperate in orioles. Where there had been a pair of orchard orioles in each of the previous two seasons, this year there were none. Where there had been 4-6 pairs of Baltimore orioles, this year all the observations pointed to a single pair. This was supported by my recently finding the nest.

Still intact, the nest contained some synthetic fibers that may have come from a disintegrated toy left behind at the nearby off-leash dog area.

The nest was at the center of the area where I noted orioles this year. Though it was right above one of the trails I regularly use, as you can see in the photo it was buried in an oak branch tip. It would have been well concealed by leaves when it was in use.

I do not know why orioles were so few this year. Without the season-long sets of observations I would not have realized there was even a difference. This exemplifies the value of frequent visits to a monitored area, and taking careful notes that can be reviewed for patterns at the end of a season.

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.

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