Almost two weeks ago we solved the mystery of what warblers were eating in the streets of south Oak Park: Beetle larvae!
Well, the beetle larvae are not longer tumbling from our elm trees, but the warblers and thrushes and Indigo Buntings keep coming, along with tanagers and orioles and more! So, to find out what the birds are eating now, I grabbed a white plastic box lid, held it under some low elm branches, and started shaking:
Here’s what I found: Little green caterpillars! (I put the dime there. Money doesn’t grow on trees in our neighborhood.)
Just in case someone out there can identify what type of moths or butterflies these become, here are some closer views:
I can’t identify the caterpillars, but I do know they taste good to birds. During the past week, we’ve seen 23 kinds of warblers feeding in and under our elm trees:
Golden-winged Warbler
Tennessee Warbler
Orange-crowned Warbler
Nashville Warbler
Northern Parula
Yellow Warbler
Chestnut-sided Warbler
Magnolia Warbler
Cape May Warbler
Yellow-rumped Warbler
Black-throated Green Warbler
Blackburnian Warbler
Palm Warbler
Bay-breasted Warbler
Blackpoll Warbler
Black-and-white Warbler
American Redstart
Ovenbird
Northern Waterthrush
Mourning Warbler
Hooded Warbler
Wilson’s Warbler
Canada Warbler
Feeding along with the warblers we’ve seen:
Yellow-throated Vireo, Warbling Vireo, and Red-eyed Vireo
Veery, Gray-cheeked Thrush, and Swainson’s Thrush
Gray Catbird
Summer Tanager and Scarlet Tanager
Rose-breasted Grosbeak
Indigo Bunting
and Baltimore Oriole
These birds are all spring migrants. The Catbird is the only one who’s likely to stay and nest in our neighborhood. The caterpillars in our elm trees have helped them survive and refuel before the next night with southerly winds to speed them on their journey north.
Did I mention that last week we found thousands of tiny caterpillar poops on our cars each morning? The polite term for caterpillar poop is frass. This morning our cars were almost frass-free, although there was lots of bird poop on our windshields.
We’ll finally get some southerly winds later this week, so we expect most migrant birds to continue north. In their wake we expect our elms to enjoy an almost caterpillar-free summer.
Now if we could just find a biological control for the bark beetles that spread Dutch Elm Disease….
Every spring there are a few days in late April and early May when we see warblers in the streets, feeding on something. Two years ago it happened in late April, as seen in these photos of Yellow-rumped Warblers on our south Oak Park block:
Well, it’s been happening again the past few days. It’s like a block party for the birds, and it got me wondering–what’s for breakfast, lunch, and dinner? What tasty things are the warblers feeding on?
My best guess was that there was some sort of insect feeding on the opening leaves of the American Elms that tower over many sections of our block. Every spring there are also warblers feeding on something in the treetops, and every year there are tiny holes chewed in the leaves:
So, I was thinking that maybe whatever was feeding on the leaves somehow fell to the ground, where sharp-eyed warblers could spot them on the asphalt and continue their meals.
To test my hypothesis, I placed a white plastic lid where it could catch whatever was falling. I left it there from late afternoon yesterday until early this morning:
Then, this morning, I brought the lid inside to see what I could find. It was covered with tiny, pale yellow grub-like insect larvae!
So, one question answered: That’s what’s falling from the trees, and probably what the warblers are eating. But many questions remain:
What are these things? Hatchling caterpillars, or some other kind of insect?
Why are so many falling from the trees? Shouldn’t they be better adapted to hang onto the leaves? Or do they “jump” whenever a bird is picking at their leaf?
Once they hit the ground, they are still alive–you can see them moving. Can they somehow continue to live on the ground, perhaps feeding on fallen elm leaves and elm seeds? If so, when they are larger and stronger, would they climb back up into the trees?
So, I guess our next challenge is to try to raise a bunch of the larvae until they are large enough to identify. And once they are bigger we can put some of them at the base of an elm tree and see what happens.
I’ll let you know what happens!
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A few hours I posted this, a Facebook friend and garden designer made this comment (Thanks, René!):
“I’m no entomologist, but after some research, my best guess is Elm Leaf Beetle. These guys feed on elms and drop to the ground in large numbers as little yellow guys to pupate. Sounds like the yellow-rumped Warblers are doing a good job of natural pest control.”
As I monitored birds this morning in Columbus Park, I did an experiment. I took photos with my iPhone and uploaded them live to Facebook. It was kind of like a virtual nature walk!
We’ve been following a neighborhood Tulip Tree as it cycles through the seasons. The last time we posted photos was way back on June 18, when the seeds were green, but ripening. The seeds remained that way through most the summer, then gradually started turning brown. Once the leaves had turned bright yellow in late October, the seeds looked like this:
The Tulip Tree seeds are framed by yellow leaves. Also note the duck-bill shaped bud to the left of the seeds.
Soon the leaves were swept off the tree by a wind-drive rain, and something — probably squirrels — found the ripened seeds to their liking. Here is one of the last remaining seed clusters, photographed in early November:
This was one of the last seed clusters remaining on the Tulip Tree.
Once the seeds have all been eaten or fallen to the ground, the tree will be back to where it started last spring.
Earlier this year Neighborhood Nature showed the earliest examples of spring flowers we could find. Now that November’s two-thirds gone, I guess it’s time to show the last wildflowers still blooming in Columbus Park. (I’ll do my best to give their names, but bear with me — I’m not a botanist!)
It was sunny and almost warm during this morning’s bird monitoring in Columbus Park. However, some parts of the Park were devoid of birds, so I had time to look down as I listened hard for any birdlike sounds. These nickle-sized flowers caught my eye — I’m pretty sure they’re Daisy Fleabane. (You can see a photo of the entire plant here.)
Although these look like daisies, the flowers are much too small. So I think it's Daisy Fleabane.
The small patch of prairie habitat beside the lagoon held two plants in flower. The first one looked like a very small example of Queen Anne’s Lace (aslo called Wild Carrot) — the flower head was less than two inches across. (You can see a photo that shows the leaves here. Please use the comments, below, to correct me if I’m wrong.)
This one looked like a very small example of Queen Anne's Lace (also known as Wild Carrot).
I’m also uncertain what this plant is called. I’m guessing this might be False Dragonhead, a kind of mint. Another name for this species is Obedient Plant, since if you push the flowers to one side, they stay there until you push them back. However, I forgot the try that test today, so my identification has not been physically confirmed. Also, this flower looked more pinkish in the field — I’m not sure why the photos don’t do justice to the color. (You can see a photo of the entire plant here.)
I'm guessing this is False Dragonhead, a kind of mint. (Again, use the comments, below, to help me out!)
My final flowers were just hanging on — most of the others on this plant had gone to seed. It was a kind of thistle, found in Austin woods — but don’t ask me what kind of thistle, I wouldn’t have a clue. (Again, these looked more pinkish in the field. You can see a photo that shows some leaves here.):
A few thistle flowers remained, but the rest had gone to seed.
“Gone to seed” is where all these flowers are bound. Food for birds, and sometimes a feast for the eyes despite the lack of color. Check out these goldenrod seeds, which may be Showy Goldenrod, one of the most beautiful of its kind. (You can see a photo that shows more of the plant here.)
Even gone to seed, goldenrods are beautiful.
So, are these the last wildflowers I’ll see this year in Columbus Park? I’ll keep looking for more on future visits. (And I’ll also try to tame that possible Obedient Plant.)
For the past few weeks our neighbors have been raking and blowing fallen leaves into the streets to be hauled away to someone else’s compost heap. Soon all out trees will be bare, and most our leaves will be gone — only memories of a leafy summer will remain.
Or so I thought. Until I saw this:
Naturally made prints of maple leaves on a concrete sidewalk.
Some leaves remained as ghostly stains on the sidewalks of south Oak Park! I found the first leaf prints after a week of wet weather had given way to the first dry day. Perhaps water-soaked leaves had been plastered to the sidewalk for days, leaching biochemical stains into the sidewalk cement.
The best individual prints were along this stretch of sidewalk:
This stretch of newer sidewalk, with widely spaced young trees, had the best individual leaf prints.
The sidewalk here was pretty new, smooth and fairly flat, and the trees were small and evenly spaced. When leaves were scrunched instead of flat, or when sidewalk blocks were tilted, the prints were less than perfect:
This leaf was scrunched up in the middle, so the print was incomplete. And the sidewalk here was tilted, so the stain left a streak mark as it leaked out from under the leaf and towards the street. (These imperfections provide clues to how the leaf prints formed.)
When trees above were large or closely spaced, the prints were crowded together and often overlapped:
When too many leaves were plastered on the sidewalk, their prints overlapped and blended together.
That must be why concrete street gutters are stained brown this time of year:
Concrete gutter stained brown by mounds of water soaked leaves.
The first prints I saw were maple leaves — I wondered if other leaves could make prints, too. Searching the neighborhood sidewalks, I found some oak leaf prints, but they were on a older stretch of sidewalk, so weren’t as well defined:
This oak leaf was printed on a stretch of older, rougher sidewalk.
Then I found some clearer oak prints on a newer sidewalk — but they were black instead of brown:
These oak leaf prints were different — they brushed away. They were made of dark, dusty dirt, not brown stain.
I looked closely and saw that these prints were made of dark dirt trapped in tiny rough spots on the sidewalk. They were dust-prints, not stains, because I could brush the prints away. I noticed that dust-prints had only formed in a sheltered spot, by a recessed door:
The oak dust-prints had formed in a sheltered spot beside a little-used, recessed door.
So, here’s my guess about how these prints formed: I think a layer of dust accumulated in the sheltered spot beside this little-used door. Then oak leaves blew onto the dusty sidewalk. The previous week’s rains had first plastered the leaves to the sidewalk — protecting the dust below — and then washed away the dust between the leaves. As the weather cleared, the oak leaves dried and blew to one side, exposing the leaf-shaped patches of dusty concrete below.
Now, here’s a question: If humans provide the concrete canvas, but nature does the rest, are these leaf prints art? I think not. But an artist inspired by these prints could make art using nature’s techniques. All that’s needed for stain-prints would be a stretch of newer sidewalk, leaves, water, and time — at least several days, I’d guess. To make the dust prints, you’d need new sidewalk, dust, leaves, and water. If I’m right about how these prints formed, you could make them in a few hours.
And if you try to do the art, you will also be testing my ideas about how the leaf prints formed. If my hypotheses prove wrong, then your art will fail, too. Hypothesis testing is science — so you’d be doing art and science at the same time!
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Go here to read about the biochemistry of leaf stains. The stains may be made by tannins, or perhaps by pigments called anthocyanins.
Ghost leaves or tannin shadows (steef’s contributions)
Leaftovers (krippledkonscious’s idea)
Foliagraph (contributed by Terminal Verbosity)
If you don’t like leaf stains and want to make them go away, try here or here. (I can’t personally vouch for either site, though — you’re on your own with this issue!)
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Note added Friday, November 13, 2009: On this morning’s walk I found examples of a third type of leaf print on a concrete sidewalk. Here’s a photo of imprints made when leaves fell onto a concrete sidewalk right after it had been poured — when the cement that would eventually bind it all together was still soft and wet:
These prints were made when Elm leaves fell onto concrete when the cement was still soft and wet.
On a 20 foot stretch of sidewalk there were at least 50 prints of two types of leaves (plus a trail of squirrel footprints — more about that in another blog post). In addition to the Elm leaves, there were also a dozen prints that looked like a type of Basswood or Linden:
These prints include a Basswood or Linden leaf above and two Elm leaves, below.
Although it’s hard to tell from these photos, the leaf prints were a couple of millimeters deep — that’s why I called them imprints. Because many of the prints were so perfect, I imagined that the leaves must have stayed in the concrete until after the cement had set, perhaps rotting in place. However, as shown in the photo above, some prints were not perfect — the leaves were folded or had slipped to one side after they had fallen into the soft cement.
So, I’m wondering if we can tell anything more from these imprints. Because there are so many leaf prints, does that mean the sidewalks were poured during autumn, when leaves were falling? Did strong winds blow the leaves onto the concrete and then fold or slide some once they were embedded in cement? Perhaps the evidence can’t rule our other possibilities, but it’s interesting to speculate.
By the way, other folks have posted photos of similar leaf imprints on the web. Some folks call them “sidewalk fossils,” and teachers sometimes use them to get students thinking about how fossils form:
Way back on June 18 we did a Neighborhood Nature blog post about Hackberry Nipple Galls, which you can read here. On this morning’s walk I found two Hackberry trees with half a dozen or more Yellow-rumped Warblers in them, hunting for bugs to eat. That got me thinking that maybe some of the bugs they were eating had grown up inside Nipple Galls. The warblers wouldn’t let me get close enough to see what they were eating, so instead I found some Hackberry leaves with lots of galls on them and took them home to dissect.
Before I picked them, the leaves looked like this — covered with nipple-shaped growths, called galls, that grew when insects called Psyllids (SILL-lids) laid their eggs on the leaves:
These Hackberry leaves are covered with Nipple Galls. The galls formed when insects, called Psyllids, laid their eggs on the leaves. The gall became a nursery for the baby Psyllids, which fed on the insides of the gall. The gall provided shelter and food at the same time.
After I cut open one of the galls on our kitchen table, it looked like this:
The cut-open nipple gall had a tiny Psyllid insect inside a hollowed-out cavity.
I cut open a few more galls, and more tiny Psyllids crawled out. They were about as big as the head of a straight pin:
The pinhead-sized Psyllid on the lower left was walking around, but the Psyllid on the upper right was upside down. You can tell these Psyllids are not yet fully grown, because they don't have wings. They just have "wing buds" behind the head, which will become wings after they shed their skins another time or two.
So, maybe the warblers were eating adult Psyllids that had emerged from galls on the Hackberry trees, or maybe they were eating something else. But what I really want to know is if any birds peck open Nipple Galls to catch the not-yet-fully grown Psyllids. (I’ve seen Downy Woodpeckers break into Goldenrod Galls, but those galls are somewhat larger.) I guess I’ll have to keep a close eye on any birds I see in Hackberry trees this fall. I’ll also search through Hackberry leaves for galls dissected by bird beaks instead of knives.
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Update added two days later (October 22, 2009): Rather than throw the gall-covered Hackberry leaves outside, we put them in a container with a lid and waited to see if adult Psyllids would emerge. When we opened the container this morning, this is what we found:
There were at least four of these winged adult Psyllids in the container with the gall-covered Hackberry leaves. (Because of the wings, they were twice as long as a pinhead is wide.)
Now, doesn’t that look like a good snack for a warbler?
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You can read more about Psyllids and Nipple Galls here and here and here.
On the first Friday in September I noticed ripe Pokeweed berries in our backyard:
These are the first ripe Pokeweed berries I've seen this year, and they are in our backyard!
Soon there will be catbirds, thrushes, and many other birds with purple-stained beaks!
Gray Catbirds have spent the last five summers in backyards on our block. They stopped defending their breeding territory weeks ago, but I’ve seen a Catbird visit our Pokeweed once or twice since then. I think they keep track of berry bushes in the neighborhood so they can be the first to feast once the berries are ripe.
Swainson’s Thrushes breed up north, and then migrate south through our area starting late summer. Yesterday I saw two in the woods at nearby Columbus Park. Last September a Swainson’s Thrush stuck around our neighbor’s yard for two weeks feeding on her Pokeweed berries. A few weeks later a Hermit Thrush stopped by to eat its fill.
One nice thing about Pokeweed is that it keeps producing berries for many weeks, September through October. In this photo you can see ripe berries and a tiny flower stalk just starting, plus all stages of flowers and green berries in between:
The ripe Pokeweed berries are hidden among the leaves. A newly opening white flower stalk is to the left and above the berries, and in between stages are scattered elsewhere on the plant. By the way, the oval leaves are Pokeweed; the larger heart-shaped leaves are a type of Morning Glory.
So, this fall’s backyard catbird and thrush watch starts today, and then continues for almost two months!
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Note added Friday, September 4, at 2 p.m.: Early this morning we saw the first bird of the season feeding on our Pokeweed. It was an American Robin (which is a kind of thrush). Then, while monitoring birds at Columbus Park (less than a mile from our house), I saw about a dozen Swainson’s Thrushes and three Catbirds. Three of the Thrushes and one of the Catbirds were feeding on Pokeweed berries.
Note added Sunday, September 6, at 3 p.m.: We just saw three Swainson’s Thrushes in our Pokeweed patch! Aaron got the following for-the-record photo through our back window:
One of the three Swainson's Thrushes we saw on our backyard Pokeweed. Note the olive-brown back, lots of spots on a pale breast, and big buffy "spectacles" around its eyes. Photo by Aaron Gyllenhaal (shot through a sunlit back window).
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You can find more information about Pokeweed on Wikipedia. Cooked Pokeweed greens can be eaten, but raw Pokeweed can be poisonous to humans, as described on this National Institutes of Health web page.
During a break in this afternoon’s rains, I was walking along our street checking for migrant birds. Something caught the corner of my eye — I looked down and found this:
I found this three-inch sphinx moth caterpillar laying motionless on the street, under an American Elm tree. The head is on the left, the hind end (with its horn-like projection) on the right.
We find at least one of these caterpillars each summer, always on the street or sidewalk under an American Elm tree. The green color, overall shape, and especially the pointed projection on the tail convinced me that this must be some kind of hornworm — the caterpillar stage of a sphinx moth.
The caterpillar was motionless. I wondered if it had fallen 30 or 40 feet from the tree above and died. Just in case it was merely stunned, I brought it in our house and put it in a plastic box with some elm leaves. When Ethan and I checked it a few hours later, it was moving its head slowly, stiffly swinging back and forth, so it was still alive. Maybe we could save it!
Then we had a brainstorm. We knew that many hornworms dig into the ground and make a pupa — the transition stage from caterpillar to moth — without spinning a cocoon. And caterpillars often stiffen up before they split their skins, revealing the pupal stage within. Maybe this caterpillar had dropped to the ground on purpose, but had the bad luck to land on the street rather than soft soil. So we added some damp sand to the box, set the caterpillar on the sand, and waited.
Two hours later Ethan checked the box — the caterpillar had disappeared! However, a bit of digging revealed that it had merely dug its way into the sand and curled up into a tight C-shape. We left it alone, because pupating caterpillars can get all messed up if you bother them during this critical transition.
We’ll check again tomorrow and let you know what happened.
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Update: The caterpillar continued burrowing in the sand, digging all around the container and finally settling into a rounded cavity just below the surface. Then, after about a week, it died without making a pupa. It turned out to be a tragedy after all. We were very sad.
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Follow these links for more information about sphinx moths:
Elm Sphinx (Ceratomia amyntor). This web page shows the Elm Sphinx as having four horns — the one we found only has one. So, even though it seems to eat elm leaves, it must be a different species.
A week ago I cut through a Buckeye husk and found the full-sized nuts were still white — not the rich brown Buckeye color that’s so beautiful. (You can see the unripe nuts here.)
Well, I set the unripe nuts and husk on a top shelf in our kitchen, out of reach of cats and squirrels. A week later, this is what I found:
Last week the unripe Buckeye nuts were white -- today they were brown and shiny!
The nuts had turned brown and shiny! However, they had also shrunken and wrinkled just a bit. The husk had shriveled and split, revealing a third nut hidden inside.
I’ve got eight or ten more Buckeye husks set aside. I was thinking of cutting them open at the block party this Saturday and making Buckeye crafts (see ideas here). But there are two things that worry me: Some kids on our block have nut allergies — would those extend to Buckeyes? (Others have pondered this question.) Also, many references say fresh Buckeyes are poisonous to fish and other living things (for instance, here). So, maybe Buckeye husking will be a demonstration and not an activity.
Neighborhood Nature 