And now they are eating…caterpillars!

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….

First Hard Freeze for Our Jars of Water

Back on November 29th we started an experiment on our front porch, with four plastic jars filled with water. At the start of the experiment, the jars looked like this:

Here's what the experiment looked like five days ago, before the temperature hit the freezing mark.

Now, here’s what the experiment looked like on Friday, December 4th, after the air temperature went below freezing, hitting 24 degrees Fahrenheit overnight:

Here's what the water jars looked like after a hard freeze. Three of the five jars had frozen overnight: A, B, and D. Also, we had added a fifth jar: In Jar E, the water that had been BOILED first, then cooled, put in the jar, and sealed with a lid that had NO holes in it. (Thanks to J of Science Museum of Minnesota for suggesting this addition to the experiment.)

Three of the jars had frozen water in them, including the jar with SALTY water. No one predicted that! The two jars that did not freeze were both sealed tight — there were no holes in their lids.

Here’s a closer look at Jar A, which started out as cold, fresh tap water, and was covered by a plastic lid with holes drilled in it:

A closer look at Jar A shows intersecting sheets of ice, more densely frozen closer to the top of the jar.

Jar B showed a similar pattern, although the sheets of ice were more horizontal than vertical:

Jar B also had sheets of ice, more densely frozen towards the top of the jar -- but the ice sheets were more horizontal than vertical.

Jar D was most surprising. I was expecting the salty water wouldn’t freeze, but the top part of the jar was frozen fairly solid. However, the bottom of the jar was not frozen, but had a bunch of bubbles sticking to the side of the jar:

In Jar D, notice the clear division between frozen water above and unfrozen water below.

So, that leaves us with two mysteries to solve:

• Why did most of the water in the salty jar freeze?
• Why did the water in the sealed jars not freeze?

I have some ideas, but I won’t tell you about them yet. However, I will give you one hint about the second mystery. Here’s what the lower part of salty Jar D looked like on December 2, 2009 — three days after the experiment started, but before the temperature dropped below freezing:

Here's what Jar D looked like three days after I had mixed in several handfuls of sidewalk salt, but before the first hard freeze. How can this help us understand why the top of the jar froze, but the bottom did not?

Feel free to tell us your ideas in the comments section (below) or on Facebook.

An Experiment with Freezing Water

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”?)

—–

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….)

—–

To find out what happened on December 4th, when the air temperature dropped below freezing, please go here: https://neighborhoodnature.wordpress.com/2009/12/07/first-hard-freeze-for-our-jars-of-water/