by Kristen Carlson
Oak Heritage Conservancy
“One Carolina chickadee breeding pair requires between 6,240 to 9,120 caterpillars to feed their brood prior to fledgling in 16 days.” Unbelievable, I thought as I listened to Doug Tallamy, as the TA Baker Professor of Agriculture and Natural Resources at the University of Delaware, said recently at the Cincinnati Zoo & Botanical Garden as part of their Barrows Lecture Series.
There is a lot of information to unfold in that single statement and how it applies to each of us. Let’s begin the unfolding.
First, the Carolina chickadee is a squirt of a bird; it’s very small, black and white in color, and is a cavity nester (often around woods and our yards). We see them year-round in our area and they often come to feeders to eat seeds. Chickadees have a variety of calls and songs; you may be familiar with the chicka-dee-dee-dee call. If you have heard this call around your home, then you’ve got chickadees and hopefully caterpillars.
Second, who made all those caterpillars? Lepidopterans, of course. Our friendly neighborhood butterflies and moths can lay hundreds of eggs each breeding season. The number of eggs laid depends upon the species. Why caterpillars and not worms (a common misconception)? Caterpillars have soft bodies with a thin exoskeleton, which makes aggressively thrusting down the throat of a nestling a little easier than say, a beetle. Worms, on the other hand, are quite wriggly, which makes them wriggle right out of the nestling’s mouth. There went dinner. But there is something even more special about caterpillars that worms can’t even touch.
Nutrition and necessary molecular compounds. Caterpillars are loaded with lots of fat and protein, which is needed to get a baby bird from hatchling to fledgling in those 16 days for our chickadee. You can’t get that nutrition from seeds and fruits alone. Caterpillars also contain carotenoid pigment molecules, which help with eye development (color perception) and feather color. Carotenoids are important molecules for our health and well-being too. Worms have negligible amounts of these molecules such that a bird’s eye development and coloration would be hindered.
Third, where do birds find all of these caterpillars? Not necessarily in your pollinator garden unless that garden also includes trees and shrubs! Tallamy found that trees and shrubs are the keystones in the yard. Keystone species (or plants) are organisms that affect an ecosystem in an inequivalent way by increasing its species amount. For example, beavers can be considered a keystone species because they convert a moving water system to a standing water system that would allow organisms that require standing water (or slow-moving water) to have their habitat needs met to complete their life cycle, such as some fish, dragonflies, mayflies, damselflies, mosquitoes, as well as willows, some grasses, various waterfowl, and even more.
If we removed the beaver, then the other organisms’ habitat needs may not be met taking with it their population. For the more than 90% of songbirds that require caterpillars as their “baby” food, trees and bushes are able to accommodate the caterpillar load to feed not only one brood of Carolina chickadees but also broods of other species.
What types of trees or shrubs are the keystones and how many butterfly and moth species can each support? Here are the big winners: Oak species support over 550 different species of butterflies and moths; Willows support more than 450 species; Maples support about 300 species with pines supporting over 200 species. And let’s not forget our blueberries, which support over 290 species!!
There are many other species of trees and shrubs that can be planted but these trees are the major keystones for the songbird populations. Without these important trees, then they would not be able to find enough food to keep their populations going.
And did I mention, that the range of the Carolina chickadee for finding these caterpillars on these trees and shrubs is only about 160 feet in all directions from the nest (and don’t forget that the adults still need to find seeds, fruits, and occasional insects for themselves in this range too)?
Finally, how can you help support the songbird population by providing for the baby birds? Add some specific trees and shrubs in and around your home and neighborhood. You can find a printable list of species of trees and shrubs to plant along with the species of caterpillars they support at: https://static1.squarespace.com/static/5a64bc3129f187b303ae782d/t/604406dc159ecb2375cf8780/1615070940134/Native+Plants+that+are+Hosts+for+Butterfly+and+Moth+Caterpillars.pdf.
Try to choose native trees and shrubs to the best of your ability as research shows that to support the populations of songbirds in their ranges for food requires them to have at least 70% natives.
Trees and shrubs contain a lot of biomass to support caterpillars large enough to be fed to birds so it doesn’t mean you have to grow one or two of each species of tree or shrub in your own yard.
Share the responsibility with your neighbors, change the mindset of some homeowner associations, businesses, and cities to grow species that support the songbird food web at all life stages. We also have to change our mindsets about having trees with holes in their leaves; it can be a good thing. Have you ever seen holes in your tree leaves but not culprit? It might be in the “belly” of a baby bird!
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Kirsten Carlson is a biology teacher at Ivy Tech Community College and the Education and Outreach Coordinator for Oak Heritage Conservancy.