Testing the Birds and Buckthorn Hypothesis

by Carl Strang

A year ago I posted a hypothesis that this most unusual of seasons will allow me to test. To recap: When restored savannas are compared to woodlands with buckthorn and honeysuckle thickets in the understory in early May, when the bird migration is entering its peak, it seems that the birds prefer the invasive-degraded areas to the native savannas. Some birders take this as evidence that restoration is bad for birds. My hypothesis was that this observation is tied to the fact that oaks, the dominant trees in our savannas and woodlands, are among the latest trees to break bud and leaf out. Therefore they are not supporting leaf-eating insects, and also not providing the shelter that the birds need on their daytime migratory stops. As I pointed out a few weeks ago, like our flowering phenology, the oaks broke buds a few weeks early this year.

Remember this photo? I took it in early April, more than a month before oaks typically reach this point.

The stage thus is set. I have the records of where I saw the migrants last year, a late year when the oaks were not leafing out until the second half of May. I remarked in my notes that they were doing so around May 19, so I will take that as my dividing point. I can look at last year’s data, and this year’s, and see if the birds lose their apparent preference for the buckthorn woodlands now that they have leafy oaks as an alternative.

As a starting point I compared the bird counts from April 20 to May 18 last year to those from May 19 to May 31, when migration was essentially done. I considered only species that spend their winters south of the continental U.S. and that do not breed on the Mayslake preserve, to keep things as uniform and unbiased as possible. Even with those restrictions, I had 22 species to work with. For the moment ignoring species by species comparisons, here are the 2011 totals. In buckthorn woodlands before May 19, I made 80 observations of birds in the target group. The corresponding total for restored savanna areas in that same time period was 34 (these counts are not normalized for the relative areas of the two habitats, but the buckthorn area I used for this comparison is smaller, at 5.7 acres, than the savanna at 8.5). So the data support the notion that, at least early in the migration season before the oaks leafed out, the lower quality, buckthorn- and honeysuckle-dominated woodland harbored more birds. What about the latter part of the migration season, after May 18? Things had slowed down at that point, and the migrant species composition changed somewhat, but the totals last year were 24 observations in the buckthorn woodland and 28 in the savannas. Clearly the tide turned after the oaks began to leaf out (for the statistics cognoscenti, the chi-squared contingency table produced a test statistic value of 14.36 at 1 degree of freedom, highly significant). I will report on what happens this year, but if my hypothesis is correct, the oak savanna should prove more attractive to these migrants this year in both parts of the season.

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Birds and Buckthorn

by Carl Strang

Birds eat bugs. That’s a 3-word description of the main action going on these days as migrant songbirds drop into our woodlands, refueling during the day before they continue on their way north at night.

Buckthorn provides no bugs, nor does honeysuckle. These Eurasian shrubs might as well be made of plastic, as far as our native insects are concerned, and so support none of the fuel needed by those feathered foragers.

So, why does it so often seem that more migrants can be found in woodlands with buckthorn and honeysuckle understories rather than restored woodlands with a diversity of herbaceous native plants beneath the trees?

This has been the hottest part of Mayslake Forest Preserve in recent days for diverse migrant songbirds. Its dominant understory plant is buckthorn. The nearby restored savanna, rich in native herbs, has some migrants, but not nearly so many species or individuals.

Some people who are excellent birders (but uninterested in ecology or any other aspect of natural history) have made similar observations, and so have a negative view of restoration.  It’s hard to blame them, given their data and focus.

So, what’s going on here? I have a hypothesis, but it needs testing (unless someone already has done so and I haven’t encountered the paper). I think the issue is security.

Here a Wilson’s warbler rests in the dense foliage of a buckthorn bush in the same area at Mayslake.

Both the savanna and the buckthorn-infested woodland have plenty of trees, and most of the insects these birds are after are feeding on the trees’ flowers and tender new leaves. The herbaceous plants in the savanna will provide abundant insects later in the season, but not much to speak of, this early. In other words, food availability probably is similar between the two kinds of places during this peak migration time (a test of my hypothesis would require measurements to confirm that statement, however).

I suspect that the buckthorn’s appeal is that it provides a ready hiding place for the migrants. They want a secure retreat if a hawk comes along, and the blanket of dense shrubbery beneath them has that quality. As dawn breaks, birds that have been flying all night are looking for a place to spend the day. Trees provide the food, and the dense patches of understory shrubs complete a clear target for weary, hungry, safety conscious birds.

Cedar Waxwing Dossier

by Carl Strang

One delightful bird which can be seen in northeast Illinois throughout the year is the cedar waxwing. Today I share my dossier for the species, consisting entirely of my own observations. Though references are valuable it also is important, I think, to keep track of one’s own experiences with a species.

Cedar waxwings are smaller than robins but larger than sparrows, crested, soft brown and yellow in color with bright yellow follow-me bands on the tail tips.

Waxwing, Cedar

My principal childhood memory is of waxwings that nested around brushy thickets and willow clumps along the Tippecanoe River near Monterey, IN. Adults hunted insects in flycatcher fashion from bare twigs over the river. In DuPage County they are evident in wandering flocks through all parts of the year except the breeding season. They travel in flocks, staying one to many days in an area and feeding on berries in fall and winter. This also occurred in Cumberland County, PA. Mountain-ash berries were a favorite food in both places. Also consumed are dogwood, and buckthorn berries. Flock cohesion is aided by the bright-yellow tips of the tail feathers, and by the unique high-pitched thin contact call. First winter birds have breasts striped longitudinally with cream and the soft brown adults’ breast color. At the Willowbrook Wildlife Center clinic, waxwings frequently came in with broken wings and other injuries suffered in collisions with windows. In the cages they showed an open-mouthed threat display, possibly made more effective by the black facial markings. In mid-September at Herrick Lake, a single waxwing perched in an old-field treetop gave a single loud note and flew away into thicker trees. Several seconds later a sharp-shinned hawk flew by the waxwing’s original perch, heading in the same direction. (This first paragraph, written from memory, established the dossier in the early 1980’s. Subsequent additions begin with date codes.)

When not feeding, cedar waxwings typically perch high in trees.

30OC86. Willowbrook Back 40. Waxwings feeding heavily from honeysuckle (berries and leaves still on bushes).

16OC87. First autumn appearance of a flock at Willowbrook Back 40.

13JA88. Lots of waxwings in Back 40.

27OC88. Feeding on honeysuckle berries, Willowbrook Back 40.

13DE88. Waxwings abundant in Back 40, stuffing down rose hips.

3SE89. Mixed young and old waxwings eating honeysuckle berries, Island Park, Geneva.

JA99. Waxwing flocks frequently at Willowbrook. Eating, among other things, Asiatic bittersweet (Celastrus) berries.

11MR99. Last of winter waxwings noted. Not seen again at Willowbrook until 25MY. Then after 1JE another gap until 12&20JL. Became a frequent visitor again in early August.

These waxwings are drinking meltwater where snow is being warmed on a roof at Mayslake Forest Preserve. Much energy is saved by drinking, even if the water is cold, instead of eating snow.

7JA00. Waxwing eating buckthorn berries.

31JA00. Waxwing, again at Willowbrook, again eating buckthorn berries.

8FE00. Waxwings eating buckthorn berries at Willowbrook.

17FE00. Several waxwings on the ground eating snow (buckthorn berries available on bushes nearby).

19MY01. Many flocking waxwings spread out over a large area at the Arboretum, mainly in treetops in forest as well as more open areas.

12MR06. Cedar waxwings delicately picking anthers from silver maple flowers in the yard. [Note: studies have shown that waxwings use protein from pollen to render certain berries more digestible]

13JE06. Tri-County State Park. Cedar waxwing working on a nest in the topmost leaf cluster in a 25-30-foot box elder within 30 yards of Brewster Creek. Weaving, using long slender strands, at least some of which are stripped from grape vines. Spending considerable time with each strand. Mate perched in same cluster of trees. Bird completely concealed when weaving.

This is the tree where waxwings built a nest at (then) Tri-County State Park in 2006.

16JE06. The nest looks complete, a significant lump in the first branching of twigs about a foot from the tip.

22MY08. Fullersburg. An interesting display between 2 cedar waxwings, appears highly stereotyped. They were perched side by side well up in a tree in SW Butler Woods. They took turns quickly hopping away from the other bird a few inches, and returning, at which point the two birds touched or nearly touched beaks, which were angled up. Each of these cycles (or half-cycles, for each bird) took 1-2 seconds, and there were perhaps 20 reps that I observed (i.e. at least 10 per bird). At first they faced the same way, at some point one turned to face the other way and they continued. Eventually one moved to a different twig, but still was close. [Note: this is called the Side-hop display in the Stokes bird behavior guide, and is part of courtship].

6JL09 Mayslake. 14 cedar waxwings foraging like swallows out over May’s Lake. (This was repeated over several days.)

1JA10. Hidden Lake. Waxwings and robins feeding on buckthorn berries.

Eastern Bluebird Dossier

by Carl Strang

A couple weeks ago I shared my dossier on the great blue heron. Today’s choice is an example of a species for which I have not made a lot of observations, and so my personal knowledge is more limited.

Eastern Bluebird

As a child, occasionally I saw these at the horse-jumping practice ground in the Culver Military Academy’s Bird Sanctuary near Culver.

They nested in birdhouses mounted on posts in a tall-grass meadow with widely scattered trees at the Tyler Arboretum near Philadelphia in 1980.

I saw them in a similar area in spring 1986 at Waterfall Glen Forest Preserve, DuPage Co. I also saw them in southern Illinois at Giant City State Park. [Bluebirds once were so uncommon that simply listing the places where I had seen them was most of what I could write when I first created this dossier].

23MR88. A bluebird singing from the top of a nest box, one of those posted out from a fencerow. [Location not indicated; Blackwell?]

29AP90. Indian Knoll Schoolyard, near Winfield Mounds Forest Preserve. Bluebird foraging on mowed lawn by perching 8-15 feet up and sallying out 20-40 feet from perch to land on ground and take food, then returning to same perch or moving to another. [I since have concluded that this version of sit-and-wait foraging is their primary hunting method. Other birds I have seen hunting in this way are Australia’s kookaburras. Of course, the latter are after larger insects, small lizards, etc.]

20FE93. Bluebirds at the boundary between Hidden Lake F.P. and Morton Arboretum.

6FE99. Bluebirds wintering in a savannah area in the Morton Arboretum.

29AP00. Apparent territorial boundary dispute between two male bluebirds near prairie at Morton Arboretum. Song “peer, peer, poowee,” wings flutter when singing. Flying bird has an appearance like horned lark or swallow.

8OC00. Flock at West Chicago Prairie.

26MY01. A protracted dispute between a pair of bluebirds and a pair of tree swallows at a nest box in the prairie area at the Morton Arboretum’s Heritage Trail. The male bluebird was at the entrance on the outside of the box, with the female on the ground nearby, when the swallows arrived. At first it appeared that the swallows were attempting to chase the bluebirds away, but then the male bluebird became vigorous in chasing after the swallows. After 5 minutes of this, the bluebirds backed off and a swallow took the perch on top of the house. Soon, though, the bluebirds returned and the male resumed his attack. I never saw any of the birds enter the house.

5JA06. Fullersburg. A small flock of bluebirds feeding on honeysuckle berries near the Visitor Center bridge. (These stayed around for another week or so).

4AU09. Mayslake. Bluebirds nesting near the chapel have fledged at least one youngster.

(Dates are coded with the day, two-letter month code, and two-digit year).

Culver Seedling Identified

by Carl Strang

This story began in February. On a visit to Culver, Indiana, I found a seedling, surprisingly sprouting in winter.

February cotyledons b

I did not recognize it, and was determined to identify it. What seed germinates that time of year? On several subsequent visits I watched the seedling’s continuing development. Here it is in mid-May.

Seedling 16MY 2b

Finally at the end of May I took the time to survey nearby plants to find the best match. By this time I was satisfied that the seedling was a woody plant, and a shrub rather than a tree or vine. Possible parent plants in the vicinity included spicebush.

Spicebush Culver b

But spicebush has an alternate leaf arrangement. I am familiar enough with two of the other 3 similar candidates to rule them out. It’s not a honeysuckle.

Honeysuckle Culver b

Leaf shape and growth form are wrong. It’s not a buckthorn.

Buckthorn Culver b

Though buckthorns have semi-opposite leaves, their leaves are toothed. Besides, buckthorn seedlings have this odd, distinctive look:

Buckthorn seedlings b

One candidate remains. I showed its photo a couple weeks ago, and Scott N. of the Through Handlens and Binoculars  blog (link in left margin of my blog’s frame) suggested common privet. I remembered encountering a colony of that European shrub at Fullersburg Woods in DuPage County last year. It was flowering in mid-June.

Common privet 1b

As I wound my way through the woods in Culver surrounding the mystery seedling’s seep, I found a lot of these shrubs. There were a few that had survived in the wet low area, but most were thriving in the drier, more elevated locations. None were flowering, but many had flower buds. They will bloom in June.

Privet Culver 2b

The type of flower clusters, their location at the tips of twigs, and their incumbent white coloration confirms the identification.

Privet Culver 3b

The mystery seedling is a common privet, Ligustrum vulgare. The limited resources I have checked say nothing about its capacity to germinate in mid-winter. That may be unusual, and my interest is reduced somewhat by the plant’s not being a native species, but the experience has been satisfying and worthwhile, nevertheless.

Mystery Seedling Grows

by Carl Strang

I paid a quick visit to Culver, Indiana, over the weekend, and had a few minutes to visit my mystery seedling. It has been largely overtopped by skunk cabbages.

Seedling 16MY 1b

You may see it as a tiny plant between the big skunk cabbage leaves in the middle of the photo. Here it is close up.

Seedling 16MY 2b

I continue to think shrub, and took a look at the nearby shrubs, seeking a match. One possibility was this:

Seedling candidate 3b

Though this candidate and the seedling continue to remind me of the bush honeysuckles, these were not flowering, and their bark was not the shredded wheat pattern of the Lonicera I know.

Seedling candidate 5b

The leaves also show more width toward the tip than I am accustomed to seeing in honeysuckles.

On a related point, the cress I mentioned in earlier posts was flowering on May 16, and proved indeed to be bulbous cress as Scott N. suggested.

Bulbous cress b

The late blooming date, white flowers and habitat are conclusive.

American Robin Dossier

by Carl Strang

 

Today’s post is another in my series of species dossiers. It begins with the summary paragraph written when I established the dossier in late 1986 or early 1987. I have edited out some less informative entries.

 

robin-1b

 

American Robin. Familiar bird of natural and artificial savannas. Primarily a summer resident, although small numbers remain in northern IN and IL around fruit-rich areas as long as winter weather is not too severe. Waves of migrants seen each spring and fall. Nest typically on branches of broadleaf trees, or in shrubs. Nest of grasses and mud, with deep inner cup. Sometimes grasses dipped in mud before delivery to nest. Eggs deep sky-blue. Young may get out of nest a short distance a couple of days before fledging, but after early-morning departure from nest they tend to travel some distance and do not return. Young scattered, tended individually by parents, who swoop and may peck at people or mammals which approach the young. Fledglings have dark spots on breast. Worms and insects hunted on ground in summer; fruit the winter food. Mulberries eaten by both adults and young in early summer. Winter berries include buckthorn, mountain ash. Song dominates habitat in early morning and dusk. A musical series of phrases, each composed of 2-3 clear, slurred whistling notes sung from mid to high perches in trees, on aerials, etc. Alarm call “cheet’-der-der-der-der.” Occasional battles, presumably territorial, take place. Striking white spots on tips of tail feathers may be “follow-me” signals. Preyed upon by cats, on occasion. When hunting worms, run 2-20 feet over the ground, stop, then may move a short distance, lean down with side of head turned toward Earth, then possibly reach down and pull up worm with beak.

26AP80. Pennsylvania. Robins, when startled into flight across the path of an approaching car, appear to use body-twisting and turning tactics more appropriate to flight from a hawk.

14JE87. Young-of-year eating mulberries at Culver Fish Hatchery.

9SE87. Large flock in Willowbrook Back 40. One ate grapes.

16SE87. In the evening, within a half-hour before sunset, robins were migrating south over Willowbrook. They flew just above treetop level, in flocks of 3-30, occasionally perching to rest for a time in the treetops, then moving on. The birds occasionally called to one another in flight, alternately flapping in short bursts, and gliding.

29AP88. A robin on a nest at Pratts Wayne Woods Forest Preserve, 6 feet up in crotch of a 15-foot, 3″dbh fencerow box elder.

7AU88. Young robin, apparently independent but still with spots, eating black cherries in Willowbrook Back 40.

30AU88. Lots in Back 40, mostly on ground but 1 in black cherry going after fruit.

5OC88. Robins eating grapes, Back 40.

6OC88. Robins eating gray dogwood fruits, Back 40.

12OC88. Robins eating honeysuckle fruits, Back 40.

17JE89. A broad-wing calling repeatedly, in north end of Maple Grove Forest Preserve. Robins definitely disturbed, with nervous dee-dee-dee’s every 20 seconds or so.

28AU89. Robins eating gray dogwood fruit, Back 40.

21OC89. Robins eating buckthorn berries, West DuPage Woods Forest Preserve.

3JA90. A robin singing very softly at Herrick Lake Forest Preserve. Temperature ~40F, sun.

 

robin-b

 

14JA90. A large robin flock, scattered in woods on ground, moving as they do when hunting worms. Ground frozen. Saw occasional reaches to turn over a leaf, but no feeding.

7AP90. Robins in forest at Winfield Mounds Forest Preserve, throwing leaves with beaks to find food.

2JE90. Culver. A robin foraging on lawn (20 feet from nearest shrub) singing, 7:30am.

14SE90. Willowbrook, robin ate a couple small grapes, swallowing them whole.

JA99. Robins present on Willowbrook preserve all winter. Heavily fruiting asiatic bittersweet (Celastrus vine) a particular attraction.

6FE99. At Morton Arboretum, in an area thick with honeysuckle beneath a mesic forest, many robins feeding on the ground, vigorously throwing leaves aside and eating very small things too quickly to identify. I dug, found a mix of insects and fruit-like items.

9SE99. 2 robins eating buckthorn berries at Willowbrook.

13OC99. Robin occasionally singing at Willowbrook.

8FE00. Robin eating buckthorn berries at Willowbrook. They are fewer and more intermittent than last winter, 1 or 2 at most at any time.

13AP00. Willowbrook. One robin chasing another in the savanna. Could robins have nested in prairie savannas in years when fire burned off the tall plants beneath the trees? They might have fledged an early brood before the new plants got too tall for them.

16AP00. Willowbrook. A robin carrying nesting material.

1JE00. Arboretum. Along the Joy Path, a robin was perched in the lower branches of a maple, well concealed from above by leaves, sitting absolutely still and barely opening its beak at intervals to give a high-pitched note, somewhat waxwing-like but louder, better defined, that was difficult to locate.

15JE00. Arboretum. Near Parking Lot 7, when I arrived around 8am, 3 robins were giving the high‑pitched thin call repeatedly, and the forest otherwise was relatively quiet. After 10 minutes, a Cooper’s hawk started calling nearby, then flew out away from the forest edge until an eastern kingbird started to chase it. It immediately turned around and flew back the way it had come, and kept going. The robins then were quiet.

16JE00. Willowbrook. In the afternoon, a Cooper’s hawk perched near the west edge of the prairie, drawing alarm calls from a robin (the hawk‑whistle warning call) and a cardinal, and a chorus of 7 loudly mobbing jays.

5JL00. Willowbrook. Many robins, adult and first‑year, on the preserve today. A young one, and also a red‑bellied woodpecker, sally‑foraging for insects, possibly flying ants, from the top of a tall dead tree near the stream. (One passing insect was observed for a few seconds before the robin flew out and caught it).

11MR01. A robin singing loudly, Timber Ridge Forest Preserve.

28JL01. A newly on-its-own robin chased a cicada through the air, the insect giving its predator-discouraging call, but broke off the chase and flew back the way it came. The robin was never close to the cicada during the part of the chase I saw.

13MR02. First morning of robin (or any) dawn chorus at my house.

Culver Seedling Check

by Carl Strang

 

I was back in Culver, Indiana, over the weekend, and stopped by the little skunk cabbage seep to check on the seedling that appeared there in February. Here is its April 25 appearance.

 

seedling-25apb2

 

It proves different from the herbaceous plants I noticed nearby a month ago. Those are not quite flowering yet, but appear to support Scott’s (of the Handlens and Binoculars blog) suggestion of one of the Cardamine cresses, probably C. bulbosa, the bulbous cress.

 

cardamine-bulbosa-maybe-1b

 

It has smooth stems, the flower buds look like their petal color will be white,

 

cardamine-bulbosa-maybe-4b

 

it will be flowering later in the spring, and this species is listed by Swink & Wilhelm as an associate of skunk cabbage and of marsh marigold, the latter of which was blooming nearby on April 25.

 

marsh-marigold-b

 

As for the mystery seedling, its leaves are different in shape and venation pattern from those of the Cardamine, and had an opposite arrangement along the lengthening stem. Furthermore, the persistent cotyledons, which always have been relatively thick and large, have me thinking shrub, now, rather than herb. Could it even be (gasp of disappointment) a bush honeysuckle (Lonicera sp.)? Some of those were present, and one of the reasons they are so successful at displacing our native plants is their extended growing season. I don’t think it is usual for their seedlings to appear so early, though, if the one I am following should prove to be a Lonicera.

Biology Along the Way

by Carl Strang

 

Though my trip to Canada had as its primary goal an exploration of the route of the Lake Michigan lobe of the Wisconsin glacier, an old wildlifer like me was not going to ignore the vegetative communities and wildlife along the way. I was especially interested in what I would find in the highway loop through Timmins and Hearst, Ontario, as I had never been in that area before. It’s far enough north that I passed a sign marking the watershed for rivers flowing north to the Arctic Ocean and those flowing south.

 

watershed-sign-2b

 

Potholes Provincial Park along Highway 101 had a little trail going to some beautiful places. The trees along the edge of this photo are black spruces, a tree of special interest because we found a couple cones of this species in the mastodon dig this summer (more on that in future posts). Black spruce was the dominant tree in many places this far north, though it no longer occurs closer to Illinois than central Wisconsin.

 

potholes-13b

 

Kettle Lakes Provincial Park has a great trail system. Here are some photos showing a segment through paper birch,

 

kettle-lakes-1b

 

another past savanna-spaced pines,

 

pine-savanna-b

 

a closeup of lichens and a club moss.

 

lichen-and-club-moss-b

 

There were edible blueberries,

 

blueberries-1b

 

beautiful bunchberries,

 

bunchberry-b

 

asters still flowering in September

 

aster-1b

 

but the changing colors of plants such as these honeysuckles revealing the season.

 

honeysuckle-sunset-setting-b

 

Signs of animal life included a beaver lodge in every little lake,

 

beaver-lodge-kettle-lakes-b

 

dew-highlighted spider webs,

 

spider-web-b

 

and a spruce grouse.

 

 

spruce-grouse-2b

Tomorrow I’ll conclude with wildlife at Nagagamisis Provincial Park.

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