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….

Look What’s Falling from Our Elm Trees!

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!

—–

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.”

Here’s a photo of Elm Leaf Beetle damage: http://www.ipm.ucdavis.edu/PMG/X/I-CO-XLUT-CD.004.html
Here’s a drawing of the Elm Leaf Beetle life cycle: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pni7403-2.html
Here’s a photo of some Elm Leaf Beetle pupae: http://www.ipm.ucdavis.edu/PMG/X/I-CO-XLUT-EA.001.html

We’ve put some of our fallen larvae (or whatever) into a plastic box with newly opened leaves–now we’ll see what happens!

—–

Here are links to our earlier blog posts about birds in our streets:

• Block Party for the Birds: Warblers and Sparrows in the Streets

• Warblers on the Rooftops, Thrushes in the Alley

• Front Stoop Birding: Warblers Come to Us

Coyote Returns to Columbus Park!

When we first started birding at Columbus Park almost four years ago, Coyotes were year-round residents in the Park. We used to find their tracks crossing the snow-covered golf course, and we sometimes saw the Coyotes if we arrived early in the morning. Some folks even said they had seen a Coyote den in the Park.

Then about 14 months ago, Coyotes disappeared from the Park. The last time I saw one there was December 18, 2008. So, I was very pleased this morning when I saw a Coyote just standing there in the middle of the golf course:

The Coyote was just standing there in the middle of Columbus Park golf course.

I only had the Sony DSC-H50 camera, with its 15 times zoom, so my photos only hint at how beautiful it was:

The Coyote kept an eye me and everything else that moved or made noise around the edges of the golf course.

I tried to sneak closer by walking up behind the golf-course sanctuary prairie, but no such luck. When I peeked around the dried wildflowers, it was gone.

So, what’s a Coyote going to eat in Columbus Park? This past summer and fall we saw lots more Cottontail Rabbits than usual, and there are still lots of Gray and Fox Squirrels in the Park. Also, the snow is melting, and small flocks of Canada Geese have been returning to feed on exposed grass. Later this spring there may be 500 or more geese visiting the Park each day. For a lighter snack, there are often 40 or 50 Mourning Doves roosting on the south sides of wooded areas. Today they were just sitting on the ground, soaking up the sunlight. If all else fails, there’s usually something edible in the trash bins near the food bank, and some folks scatter bread to feed the wildlife.

So, it seems an enterprising Coyote could make a life for itself in this Chicago city park. We’ll see if this one sticks around.

—-

For lots more information about the Coyotes that live in the Chicago area, check out The Cook County, Illinois, Coyote Project: Urban Coyote Ecology and Management.

More Great Horned Owl Pellets at Columbus Park

It’s been a busy month at work, but this morning, for the first time in two weeks, I monitored birds at Columbus Park. I saw 13 species of birds, including a Red-tailed Hawk whose tail was a mix of banded juvenile feathers and bright red adult feathers. However, I did not see the on-again-off-again Great Horned Owl who sometimes roosts in an oak tree on the west side of the Park. (Read about it here.)

I always enjoy seeing the owl, but when the owl’s gone I’m not too sad, because then I can search for owl pellets under its roosting tree. The pellets I’ve found so far (shown in this post) contained a mix of medium and small mammal bones, but no teeth. So I figured the owl was feeding on squirrel, rabbit, or maybe possum-sized mammals. Since I can’t often identify bones to species, I was really hoping to find some owl pellets with teeth or jar bones, which I often can identify. Today I lucked out:

Pellets spit out by the Great Horned Owl who sometimes roosts in Columbus Park. The large, snow-crusted pellet on the right includes a lower jaw. (Taken with my iPhone.)

Here’s a closer look at the jaw:

I dug the jaw out of the frozen pellet so I could see the teeth. With the front gnawing teeth and grinding cheek teeth exposed, I recognized it as the mandible (lower jaw) of a Cottontail Rabbit. (Taken with my iPhone.)

Go here to see a photo of a complete Cottontail Rabbit skull with mandible.

This fall we had lots more rabbits than normal in Columbus Park, and I’d noticed gnawing damage to shrubs and small trees that was probably the work of rabbits. My neighbors in Oak Park had also noticed more rabbits in their yards this year and complained about damage to their gardens.  So, now there’s evidence that our Great Horned Owl is bringing the rabbit population back to normal.

—–

Here are links to information and activities about owl pellets:

• Wikipedia on pellets made by owls and other birds of prey

• A virtual owl pellet dissection

• A chart showing the kinds of bones found in owl pellets (pdf file)

A January Walk through Columbus Park

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!

Here the link to the public Facebook album with this morning’s photos:  A January Walk through Columbus Park.

Please let me know what you think!

A Red-tailed Hawk is Hunting the I-290 Median!

For the past three days a Red-tailed Hawk has been hunting from lamp posts at the end of our block:

The Red-tailed Hawk sits on lamp posts at the end of our block. The posts are in the grassy median between the east- and west-bound lanes of Interstate 290 (also called the Eisenhower Express, the Ike, or the Congress).

I first noticed the hawk on Monday while I was walking to Maze Library across the Ridgeland bridge. I saw the hawk flying from post to post, approaching me from the east. Once it got close enough, I recognized it as the pale-bellied Red-tail that I’ve seen in Columbus Park, about a mile east on the expressway:

The Red-tailed Hawk's chest and belly look distinctively pale compared with other local Red-tails.

A few weeks ago I watched this hawk hunting Mourning Doves behind the Refectory at Columbus Park — it failed rather miserably. On Monday the Red-tail made a pass at Pigeons roosting on the apartment building at the end of our block — another fail. Then it flew directly at the large Red Cedar in our alley where House Finches and Goldfinches roost — the small birds scattered, and the hawk was not even close to scoring a meal.

Since then, every time I see the hawk it’s sitting on a lamp post:

The I-290 Red-tailed Hawk in south Oak Park.

It’s always look down, at least when it’s not looking at me. It’s probably hoping for a glimpse at a potential meal — a mouse, perhaps a rat, maybe a rabbit brave enough to cross three lanes of traffic.

I hope the hawk is more successful with mammals than it is with birds. And I hope it understands the dangers of speeding cars and trucks.

The I-290 Red-tailed Hawk on a distant lamp post.

——

Red-tailed Hawks often hunt along highway right-of-ways. Here are some links that discuss this aspect of Red-tail natural history:

• Chesapeake Bay Journal: Red-tailed hawk haunts nation’s highways, fields in quest for prey
• Perch and Habitat Use by Red-Tailed Hawks and American Kestrels (Kansas; scientific journal)
• Red-tail hawk nearly plucked on Highway 17 (South Carolina)

Our Chicago Urban Christmas Bird Count Data 2009

The boys and I spent the entire day conducting our part of the Chicago Urban Christmas Bird Count. Nationally, Christmas counts are organized by the National Audubon Society. The Chicago Urban count circle is sponsored by Evanston North Shore Bird Club and Chicago Audubon Society, with Jeff Sanders as the compiler.

Our part of the count covers the following areas in Chicago and Oak Park: Birding on foot in Columbus Park, Douglas Park, and south Oak Park residential areas; feeder watching at our home on South Elmwood in Oak Park; and driving through industrial and residential areas in between these sites.

This year, birding from sunrise to sunset, we found a total of 26 species. The highlights of our day included:

• Four species of hawks, including a MERLIN at Columbus Park (photo below), 2 AMERICAN KESTRELS, 2 COOPER’S HAWKS, and 2 RED-TAILED HAWKS.
• A WINTER WREN beside the Columbus Park lagoon (where we saw this species often through the fall — photo below).
• An AMERICAN PIPIT at Columbus Park, in the same field where we saw a Pipt on December 11 (photo below).
• A SWAMP SPARROW at Columbus Park (photo of its rump, below), plus 20 AMERICAN TREE SPARROWS (15 at Douglas, 5 at Columbus).

We were also pleased that WHITE-BREASTED NUTHATCHES put in 2 appearances, since we’ve been seeing them much more frequently this year. We also were happy to see a BLUE JAY, because they were common this summer, then mostly disappeared within the last few weeks. We were disappointed that overall sparrow numbers were down at Douglas Park, where the golf-course sanctuary often holds 50 or 60 sparrows this late in the year. And we were very sad that we did NOT see the Great Horned Owl that had been roosting near Austin in late November and early December. (We still hope it returns in time to be registered as a count-week species!)

Here’s our entire list for today, with count numbers:

Canada Goose    280

Cooper’s Hawk     2

Red-tailed Hawk     2

American Kestrel     2

Merlin     1

Herring Gull     1

Ring-billed Gull     5

Rock Pigeon     115

Mourning Dove     45

Downy Woodpecker     4

Hairy Woodpecker     3

Blue Jay     1

American Crow     9

Black-capped Chickadee     9

White-breasted Nuthatch     2

Winter Wren     1

American Robin     55

European Starling    350

American Pipit     1

American Tree Sparrow    20

Swamp Sparrow     1

Dark-eyed Junco     25

Northern Cardinal     21

House Finch     14

American Goldfinch  30

House Sparrow     180

We also have two count-week species so far for our areas:

1 Red-bellied Woodpecker  (seen in Douglas Park 12/17/09)

2 African Collared-Dove and/or African X Eurasian Collared-Dove (seen in south Oak Park 12/18/09).  We are soliciting input on these photos, taken on Dec. 18th — what do you think they are?

• http://www.flickr.com/photos/36234902@N00/4196043460/in/set-72157623026500738/
• http://www.flickr.com/photos/36234902@N00/4196043362/in/set-72157623026500738/
• http://www.flickr.com/photos/36234902@N00/4195286623/in/set-72157623026500738/

Here are some of Aaron’s photos from today:

The Merlin roosted in several trees around the lagoon, but it was tough to get a good photo because of the distance and overcast skies. Note the back color, streaking on the side of the breast, and minimal patterning on the head (all of which we could see much better through our binoculars). Photo by Aaron Gyllenhaal.

This shot, from even further away, gives another view of the Merlin's head. Photo by Aaron Gyllenhaal.

Although it was hard to get a clear shot at the Winter Wren, a few times it hopped into the open, possibly to get a better look at us! Photo by Aaron Gyllenhaal.

There was a large, if late, migration of American Pipits to inland parts of Chicago earlier in December. We were happy that one stuck around Columbus Park for the Christmas Count! Photo by Aaron Gyllenhaal.

Here's a front-on view of the American Pipit. It was hanging out at the north end of the large ball field that fills the southeast corner of Columbus Park, sometimes visiting a seepage area that has some unfrozen water. Photo by Aaron Gyllenhaal.

Although we got good binocular views of the Swamp Sparrow's gray-patterned head, Aaron only got photos of its butt! Photo by Aaron Gyllenhaal.

We’ll post links to Ethan’s photos once he gets them online.

No Owl Today, Just Fast-Frozen Owl Pellets

The neighborhood crows and I were both disappointed that we didn’t find the Great Horned Owl in its usual roosting tree in Columbus Park. Here’s what the owl looked like yesterday afternoon — the third day in a row we had seen it in exactly the same spot in a White Oak tree:

Yesterday at 2:15 p.m. the Great Horned Owl was in its usual White Oak roost in Columbus Park.

This morning I looked at the same tree from every angle — and every tree around it — for 10 minutes and couldn’t find the owl. Then five minutes after I gave up a flock of Common Crows flew into the roosting tree and landed in its upper branches. These were tough crows! I had earlier seen them harassing first an American Kestrel and then a Red-tailed Hawk. I figured they knew something I didn’t — after all, crows first found this owl for me on November 24th. So, once the crows flew off, I went back to the roost tree and looked again.

Still, no owl.

I should have been disappointed, but I looked at the bright side. If the owl was in its roost, I would have backed off and left it alone. Since there was no owl to scare off, I could go look for owl pellets under its roost. (Owl pellets are the remains of animals that the owl ate — whole or in really big chunks. The pellet is the regurgitated remains of the owl’s meal, after the flesh and guts have been digested.)

Here’s what I found:

The owl pellets are the fuzzy-looking gray things on top of the leaves. The gray fuzz is fur from whatever the owl ate. The white and yellowish bits embedded in the fur are bones from prey animals.

The more I looked, the more I found:

This pellet -- about two inches across -- had more and bigger bones. When I picked it up, I saw ice crystals among the fur. When the owl spit out the pellet, it was still wet with stomach fluids. After the moist pellet hit the leaves, it froze solid.

The last pellet I found was the biggest and the boniest:

The longest bone in this pellet is about two and a third inches long. It's a humerus, the upper bone from a front leg. I'm guessing it came from an animal bigger than a squirrel, maybe a rabbit or a small opossum or raccoon.

I saw one rodent or rabbit front tooth in a pellet, but the rest of the visible bones were from legs, feet, hips, shoulders, or backs.  I’m not good at identifying animals from their limb bones — I need to see teeth.

I guess we’ll go back at some point and dissect some of the pellets. If we find some jaws or skulls, we’ll know better what our urban owl was eating in Columbus Park.

Then we’ll wash our hands really well. After all, we’ll be handling owl vomit!

—–

We found more owl pellets on January 31st, including one containing a rabbit jaw. You can see them here.

—–

Here are links to information and activities about owl pellets:

• Wikipedia on pellets made by owls and other birds of prey

• A virtual owl pellet dissection

• A chart showing the kinds of bones found in owl pellets (pdf file)

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/