The weather forecast says we’re headed into an extended spell of cold weather, with freezing temperatures predicted for the end of the week. So, it’s time to put some water jars on the front porch to see what happens. This year we’re going to be a bit more organized than usual and set up the jars as an experiment. There are reasons we’re setting it up this way, but we’ll let you try to figure out what those reasons are (with a few hints at the end of this post).

First, here’s our experimental setup: Four PLASTIC jars of water set on our front porch rail this afternoon, here in Oak Park, Illinois:

Here are our four experimental jars of water (all made of plastic). Read the descriptions to see how they differ from one another. We started this experiment on November 29, 2009.

Jar A, on the far left, was filled with cold, fresh tap water. It’s lid has holes in it, so air can get in.

Jar B, just left of center, was filled with warm, fresh tap water. It’s lid also has holes in it, so air can get in.

Jar C, just right of center, also was filled with warm, fresh tap water. It’s lid has NO holes in it, so NO air can get in.

Jar D, on the far right, was filled with cold tap water, then a couple of handfuls of rock salt were added — the same kind of salt you may put on your steps or sidewalk when it snows. It’s lid has holes in it, so air can get in.

So, we are experimenting with the following variables:

• Does the water start out cold or warm?
• Is the water exposed to the air or not?
• Is the water fresh or salty?

Why do we want to experiment with those variables? Maybe you can guess if you check out these blog posts from last winter:

• Imported Water Turns to Ice

• Hurrah! The Ice and Snow Are Back!

• Salty, Super-Cooled, Heat-Sucking Slush — and Homemade Ice Cream

And now, here’s the big challenge:

What do you think will happen to each jar once the weather gets really, really cold?

You will need a separate guess — or “hypothesis” — for each jar, A through D. You can list your hypotheses in the comments section, below, or send them to me by e-mail (eric@saltthesandbox.org) or Facebook.

Think hard, and good luck! (Or should I say, “good skill”?)

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Note: I revised this post later the same day to make it clear that the jars are made of plastic. (Although it might be fun to try it with glass some day. Fun in a Mythbusters kind of way….)

Late this morning I saw at least 14 American Crows in Columbus Park. To me that’s really great — I love crows, but their local population was decreased a few years ago by West Nile Virus. Now that they’re coming back, there’s reason for excitement — you never know quite what’s going to happen when crows are around.

The first crows I saw — a group of nine — were foraging in the woods by the lagoon. Two of them were tearing up a hornet nest. (I’ll post about that later.) They took off when they saw me, heading east and out of the Park.

The next group of crows was only five in number, but they were making lots of noise when I encountered them in the woods along Austin. At first I figured they might be looking for hornet nests — they were in the same trees where I found the nests in this blog post. But they just landed in the trees, took off again, circled over the golf course, then returned to the same trees — calling constantly. The second time they landed it was obvious that they weren’t just calling — they were calling at something. It seemed that they might be “mobbing” a hawk, so I scanned the trees with my binoculars. I thought I might find a Red-tailed or Cooper’s Hawk, which are common in the Park. Instead, this is what I saw:

The crows had located a Great Horned Owl -- the first owl I had ever seen in Columbus Park.

The Great Horned Owl was the very first owl I had ever seen in Columbus Park! A few minutes earlier I had walked right under that tree, scanning the surrounding tree tops as I went, but I had completely missed the owl. Good thing the crows helped me out — the owl was sleeping away the day in a White Oak tree. Oaks hold their leaves longer than the other trees in Columbus Park, and the leaves helped hide the owl from view.

I walked a little closer, taking photos as I went. I got within about 75 feet and took this shot:

This closer view shows the owl's tufts of feathers, which look like horns to some. It also shows the white neck band, which helps distinguish Great Horned Owls from other species with horn-like tufts.

After a few more photos, I backed away. The crows had left, and I decided to do the same. Time to let the owl get back to sleep.

I hope the crows stick around all winter and beyond. Who knows what they’ll find next time! And I hope the owl finds lots to eat tonight in Columbus Park.

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.

You can see our first photos of Tulip Tree buds at the bottom of this post from April 8, 2009.

Go here for our most complete post about Tulip Trees, which starts with the flowers and then goes back in time to how the tree looked as the buds were opening.

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.)

Now that most trees have lost their leaves, we find out what was hiding in their branches all summer long. Bird and squirrel nests are suddenly visible, and hornet nests turn out to be much more common than we ever imagined. I almost never see a Bald-faced Hornet in summer, but now I’m finding their nests in many trees in Columbus Park and throughout our Oak Park neighborhood. They look like big gray basketballs silhouetted against the sky:

Hornet nests look like big gray basketballs or balloons stuck in trees.

But when you get closer, you can see the arcs of hornet-made paper, glued by hornet “spit” to build the outer layers of the nest:

Hornets chew up dead wood, mixing it with saliva to make their own brand of paper.

Some brave creature tore off the bottom of this nest:

I'm hoping whoever tore into this nest waited until all the hornets were gone. (Worker hornets die off each fall, and next year's queen hornets burrow into soil or rotten logs to spend the winter in suspended animation.)

The outer layers of protective paper were torn away, exposing the inner cells — hexagonal tubes that look a bit like honeycomb:

Although the inside of a hornet nest looks like the honeycomb inside a bee hive, hornets build their entire nest with home-made paper (not beeswax).

Now, I’m not going to get all didactic and lecture you about the differences between honeybees and hornets. Let’s just say they both sting if you get too close, you’re not going to get much honey from a hornet, and honeybees won’t help control the fly population around your home. If you want to learn more, check out these online references:

• Who Are You calling a Bee, Mister?! Identifying Bees, Wasps, Hornets and Their Nests
• Wikipedia on Bald-faced Hornets
• Iowa State University on Baldfaced Hornets (I guess there’s more than one way to spell it.)
• Ohio State University Honey Bee Laboratory on Paper Wasps and Hornets
• Wikipedia on a bunch of other wasps that are also called hornets

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One of my Facebook friends had some advice for anyone who might consider bring a hornet nest inside for the winter. Patrick wrote, “I remember, as a kid, bringing one inside before the cold had done its deed to the hornets.” In other words, wait until there have been a couple of good hard freezes to kill off any remaining hornets (or other insects) inside the nest.

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P.S. Thanks to the Columbus Park walker who told me where to find the broken-open nest!

For the third day in a row we had a juvenile Cooper’s Hawk trying to pluck House Sparrows from our backyard brush pile. For the third day in a row it came up empty clawed.

Here’s is Monday’s drama. The hawk kept trying to find a route to the very center of the brush pile, where a sparrow cowered on the ground:

As the hawk jumped down to the far south corner of the brush pile, the sparrow scrambled out from the north edge and took off, flying over the fence and through the neighbors’ yards. The Cooper’s Hawk followed as fast as it could, but gave up four backyards north. It flew back to our yard and landed on the fence, were it was greeted by a Gray Squirrel:

Juvenile Cooper's Hawk faces off with a Gray Squirrel. This time the squirrel blinked first, jumping down to forage while the hawk held its perch.

I thought we would be in for another bird-mammal confrontation, which our Cooper’s Hawks always seem to lose. Instead the squirrel calmly jumped into our backyard, where it resumed foraging for stray sunflower seeds.

Since then, we’ve seen the juvenile hawk on our brush pile at least once a day. Each time the sparrows wait until the hawk is on the south edge of the pile, and then they flee to safety.

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.

Here’s someone else who blogged about this topic: Leaf Shadows: Stained Concrete.

Go here to contribute to a debate on “Is there a name for the stains left on sidewalks by fallen leaves?” Here are some of my favorite contributions from that debate (beyond “leaf stains”):

• 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:

• Sidewalk Fossils lesson plan
• Schoolyard Geologist lesson plan
• Another Sidewalk Fossils lesson plan

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If you’d rather make your leaf prints in a more portable form, here are some web pages to help get you started:

• The Naturalist’s Apprentice: Making Leaf Prints
• How-to: Hammered Flower and Leaf Prints
• Bluebird Paperie: Natural Leaf Prints

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This afternoon Ethan was raking leaves when he found a beautiful, silky brown caterpillar on the curb, under dead elm leaves:

Ethan found this caterpillar, a bit more than an inch long. Can you tell which is the head end? (If you guessed the left end, then the caterpillar escaped with head intact, you silly bird!)

This caterpillar probably fed on leaves this summer and early fall. Now it’s looking for a safe place to shed its skin and enter a resting stage, while it changes into a moth. (The resting stage is called a pupa, which may or may not live in a cocoon.)

But, what kind of caterpillar is it? What kind of moth does it become? My old moth and butterfly field guides did not illustrate a match, but we did find a somewhat similar caterpillar pictured online. So, maybe it’s the caterpillar of the Sloping Sallow moth — or maybe it’s not.

We released the caterpillar in our rock garden, which has lots of good places to hide and make a pupa.

If you can help us identify this caterpillar, please leave a comment, below.

According to the closest Oak Park weather station, the temperature hovered just above freezing early this morning. But skies were clear, so heat radiated from the upper layers of our backyard pools. By dawn we had our first backyard ice of the fall:

Ice formed as heat radiated from the surface layer of water.

If it had been cloudy, or if there had been a breeze to circulate the water in the pool, we wouldn’t have had ice. But with a clear sky and calm air, we got these fantastic ice patterns right outside our back door!

Why the triangles in the ice? I’m not sure, but that’s the pattern we got last year in similar situations. If you look at this blog post from last February, you’ll see another example of triangular-patterned ice. That post talks about “wrinkles” forming in the super thin ice — maybe triangles develop where three wrinkles intersect. Anyway, that’s a puzzle for me to work on over the next few months.

As part of the World Wide Web, this blog is legally and morally obligated to display photos of cute mammals at least once a quarter. However, because we show so many photos of birds and insects, we have probably fallen behind on this responsibility. Granted, we posted a photo of our kittens back in March. And many people would consider our Possum from back in February to be cute in a homely sort of way, even if you had to wade through worms and millipedes to see the cuteness. But I guess our squirrel photos tended to look either really tough, like the one from last week, or kind of demonic, because of the flash effects on their eyes.

But now, how can you say this photo of a vole from Columbus Park isn’t cute?

It’s really round and fuzzy, right? With tiny little ears? And it eats plants? Granted the eyes are small and beady, but check this out:

The tail (yellow arrow) is really short! That means it's not a house mouse!

If you look really close, you’ll even see some short hairs covering the tail. That’s pretty good for an urban rodent!

So, I think Neighborhood Nature has met its cuteness obligation for the fall quarter. If you disagree, then next time I go to Columbus Park I guess I’ll have to carry a tiny costume in my pocket, so I can dress our vole as a cat.

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If you want to get serious about voles, you can go here or here.