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June 2, 2022
Birds see the world differently than we do. We see in red, green, and blue – but birds see a fourth “primary color.” Thanks to an additional photoreceptor in their eyes, they can see UV or near-UV light. Maybe that’s why a chickadee can make a living hunting insects on chokecherries.
Insects on the menu
I see birds feeding in chokecherries all the time. Picture a chickadee flitting from twig to twig, actively probing the leaves. Obviously it’s finding something to eat – but what, exactly? I know this type of foraging behavior means insect-hunting, but I’ve never looked closely enough to find the insects themselves.
It’s not just chickadees that hunt here. Throughout spring migration, chokecherries are magnets for Wilson’s warblers, American redstarts, western tanagers, yellow-rumped warblers – the list goes on. Why? All of these birds feed heavily on insects and other invertebrates – and chokecherries support a lot of them.
According to the National Wildlife Federation, around Helena, Montana “a lot” means 227 species of caterpillars. And that’s just butterfly and moth larvae! Chokecherries must host other insects, too, but I have no idea how many species.
A closer look
What’s out there in the chokecherries that a songbird could eat? Today I’m going to pretend I’m a chickadee and try to find out. I’m at East Helena’s Kennedy Park, a beautiful natural area along Prickly Pear Creek with an abundance of chokecherries and cottonwoods. What invertebrates are these chokecherries supporting?
I’ll start with a careful search of the foliage. I’m especially looking for caterpillars, but any invertebrate I can see on the chokecherries is fair game. Right now it’s 10:32 a.m., 57°F, and partly sunny. Ready, go!
A tan pinhead of a spider rappels from a chokecherry flower, then winches itself back up.
A lone ant crawls along a leaf.
A few of the leaves have holes in them: something has been feeding here. I even find some partially completed holes. Something has almost cut these neat circles out of a leaf but left them in place, hanging by a margin. They’re like miniature chokecherry-leaf lids. I have no idea what has left this sign. Do you? If so, please leave a comment!
Ants seem common here – by now I’ve spotted five of them. If I were a bird, I’d be having a very crunchy breakfast this morning. Lots of exoskeleton with a dash of formic acid: so far this menu doesn’t seem very exciting.
On the underside of a discolored leaf is a small aphid colony. Yum, juicy! But I notice the aphids have a fuzzy whitish coating on their abdomens. Maybe not so yummy? I carefully remove one from the leaf and pop it in my mouth. The flavor is unremarkable, maybe slightly peppery. But then I notice a strange sensation… The aphid gives my tongue a chalky, dry feeling. Not such a nice snack, after all.
Harder than it looks
By now I’ve been searching for 15 minutes. I’ve found seven ants and 10 aphids, none especially appetizing. If I were a bird, at this rate I’d die of starvation before too many days passed. Although a sharp-shinned hawk might catch me first. And to think that baby birds learn to efficiently hunt insects in a matter of weeks!
I notice a few tiny flies, at least three different species. If I were a chickadee, could I catch them? Maybe. But although I’m pretending to be a bird, I’m still just a mostly-hairless mammal with bad reflexes. The flies fly away.
I find a suspiciously rolled-up, warty-looking leaf. Is there a juicy caterpillar inside? No, but I find five green aphids and a pugnacious ant that crawls onto my hand. After my last aphid experience, I don’t try eating these ones.
I spot a medium-sized, bristly black fly resting on a chokecherry leaf. I manage a photo from two chickadee-lengths away. The fly takes off. I wonder if chickadees can sense disappointment. Do they ever feel like breakfast is a sure thing, only to have it fly away? Just imagine sitting down to a lovely plate of eggs and toast only to have it leap out the window.
Aha! Here’s a group of three leaves that are conspicuously stuck together. I carefully pry them apart. Inside are five tiny, black-headed caterpillars in a silk nest. Finally, my first palatable chickadee food this morning! Since I am only an imaginary chickadee, I don’t eat them. Instead, I try to replace the leaves the way I found them, the caterpillars tucked inside.
The chokecherries here have just recently begun to bloom. The day is warming up and I spot a few honeybees over my head, methodically going from one flower to the next. I suspect they might be too flighty for a chickadee to catch. Kingbirds, though, are well-known for hunting bees and wasps, and I wouldn’t be entirely surprised to see a chickadee pull it off. If aphids taste chalky, I wonder, how do honeybees taste? Just kidding! Birds may be able to feed on stinging insects, but I think I’ll pass.
Now I’m an hour in on my chickadee simulation. Lunchtime is approaching, and I’m getting hungry. It’s good I brought lunch with me – the insects I’ve found wouldn’t fill up a chickadee, let alone me! Insect hunting has been way harder than I expected. If I ever get reincarnated as a bird, I wouldn’t bet on my survival. Of the 227 caterpillars these chokecherries may support, this morning I’ve found just a single beakful of one species. Besides that, there have been a variety of nimble, wary flies, some chalky-tasting aphids, and some fierce and crunchy ants. (I didn’t actually eat an ant today, though I have in the past. Ants are okay. Better than aphids, with an interesting sour note.)
So far, today’s insect hunt has been underwhelming. To be fair, the birds haven’t been very enthusiastic about the chokecherries this morning, either. It seems that peak spring migration has passed – or maybe we’re just in a lull. Three days ago, Carmen Winslow and Pat Grantham counted 22 western tanagers here, but today there are only a few. In the chokecherries so far, I’ve just seen one black-capped chickadee and one yellow warbler actively foraging. But are the insects actually scarce here today, too? Or is it just that the bulk of the spring migrants have moved on, leaving a few stragglers along with the summer breeding birds?
A different tactic
Clearly my inferior vision isn’t providing any answers. So now I’m going to upgrade my tools. Instead of using my eyes to search, I’m going to sweep the chokecherry foliage with my insect net. I’ll use an aspirator to suck what I catch into a vial, then put the vial in an ice-filled cooler. Once the chilled insects stop moving around, I’ll be able to take photos and get a close look at them. After a while, they’ll warm up again and fly off.
I spend just under an hour sweeping chokecherry foliage with the net, then transfer the insects to ice. While I’m waiting for them to cool, I get a tarp from my car. I try setting it up under the chokecherries and then shaking the canopy. Will I find caterpillars that I might have missed by sweeping?
My brief tarp experiment proves mediocre. I do find several new spiders, and an inchworm [the larva of a moth in the family Geometridae]. Otherwise, the tarp gets me nothing.
By now the vials of insects I caught sweeping have chilled enough. It’s time to see what we have and then let them go. I had intended to sort these into apparent species and get a tally of each, but that proves to be more than I can keep up with. Insects are waking up and scrambling away, and I’m just rushing to get photos of as many as I can.
Most of these insects are tiny; it seems I was looking too large before. It would be easy to overlook these little creatures in a visual search – but maybe an experienced chickadee would notice them.
The diversity that I’m seeing now is exciting. There are tiny, bright green wasps that would be invisible against a chokecherry leaf. Medium black wasps. An orange wasp. I see several types of bees. There’s an orange weevil with a magnificent snout. A compact black beetle. With my macro lens I see tiny, intricately patterned flies. In just this small sample, there are dozens of species.
Enough for lunch?
So much complexity in one chokecherry patch! But although there’s lots of diversity, the biomass of these insects is very low. Is this why I am seeing so few birds feeding here today?
I end this foray with more new questions than I answered. Is such low insect biomass “normal” for this patch at this time of year? I found just two species of caterpillars today – where are the other 225? Are the insects so sparse because the migrant birds have eaten them all?
How often do birds land in a promising patch of shrubs and find these sparse-insect conditions? Do they have a fast way of finding productive patches?
A logical next step might be to sweep these chokecherries on a day when they are overflowing with foraging birds. When dozens of warblers and tanagers are feeding here, we might expect to find much more insect biomass. But would we, in fact, or are birds just that much better at insect hunting than I am? Would we find greater diversity, too?
I hope to revisit these questions next spring, on a day when the migrant birds are out here in force. In the meanwhile, do you have a chokecherry patch where you spend time? Are you seeing any caterpillars on your chokecherries this spring?
I’d love to hear your observations and thoughts! If you have something to add, please leave a comment below.
Heinrich, Bernd & Collins, Scott. (1983). Caterpillar leaf damage, and the game of hide-and-seek with birds. Ecology 64(3):592-602. https://www.researchgate.net/publication/271684947_Caterpillar_Leaf_Damage_and_the_Game_of_Hide-and-Seek_with_Birds