By Frank Landis, Chair Conservation Committee
This was inspired by the opening plenary talk by Dr. Doug Tallamy at the 2018 CNPS Conservation Talk. If you were there, hopefully this will look vaguely familiar.
If you don't want to read this column, here's the gist: ecosystem ecology. If you like birds in your yard, most of our birds get their protein from invertebrates, which depend ultimately on plants. Therefore, if you want more birds breeding successfully in your neighborhood, you need to grow more bird food, and that means...having more native plants in your yard. But it's not quite that simple. Here's why:
The basic biology may actually surprise people: many, perhaps most, birds need more protein than they get from plants. The adults may get by on seeds (at least when seeds are available), but their chicks need bugs to get the protein they need to reach maturity. Dr. Tallamy even had a heart-breaking picture of a failed chickadee nest with dead chicks surrounded by birdseed from nearby feeders. In the absence of bugs, the chickadee parents had tried in desperation to feed their chicks bird seed. It didn't work.
There is a mismatch between our invertebrate fauna and much of our garden flora. Suburban gardens are hodgepodges of plants, bought mostly because they're cheap, pretty, often easy to grow (too often a euphemism for invasive). Few of them are native to where they are sold. As a result, few of the native insects can eat them. This is good if you want a pretty garden, bad if you want anything like a functioning garden ecosystem that supports young birds. Without insects eating the plants, there isn't enough for the chicks to feed on.
Yes, yards are problem spaces for insects, and we make them so deliberately. We may douse our yards with insecticides to make the plants look better, smooth edges, glossy green leaves, the whole thing. Gingko trees are notorious in this regard. They've grown only in gardens for something like 2,000 years, and while they're the poster bonsais for garden conservation, it appears that all the insects that specialized in eating them have gone, leaving a few generalists like the omnivorous looper to munch on them. I could go on, but if you've got a well-pesticided yard that's full of ginkgos and their less-munched fellow travelers, it's unlikely that you have many birds in your garden, and those that are there are clinging to your bird feeders for dear life.
You might object and point to the aphids smothering your milkweed, but that's kind of missing the point. Birds, apparently, like bigger prey, especially caterpillars and spiders. Forcing them to eat aphids is sort of like me forcing you to eat a diet of peas picked off the table without a spoon—it may be nutritious, but peas are really small and not a complete diet, and that makes them inefficient to gather and insufficient to live on.
Yeah, yeah, yeah, this is just a fancy way of saying that we should all plant butterfly gardens, right? No, it isn't. Tallamy's saying we should plant caterpillar gardens. There are two differences between planting for butterflies and for caterpillars. First, butterfly gardens tend to focus on the flowers that adult butterflies feed on, less on the food plants for the caterpillars. Can't have one without the other. The bigger problem is that something over 90% of caterpillars are from moths, not butterflies. Most lepidopterans are moths, and butterflies are better thought of as showy, day-flying moths. While it's easy to get a list of food plants for butterflies in San Diego (one is offered for sale at every chapter meeting), there's much less information on moth caterpillar food plants.
Still, there is some data, and it suggests California's a little weird. In the eastern U.S., oaks (Quercus) are by far the best host trees for insect species. In California, oaks appear to be #2 after willows (Salix). Still, if you have willows and oaks in your yard, you've apparently got a lot of bases covered.
But wait, you hypothetically stammer. Willows get riddled by Kuroshio Shot Hole Borers, while oaks get decimated by Gold Spotted Oak Borers, and OMG, that's going to cost a fortune to take out those big, old, dead trees, and chip them down to tiny shreds...I can't. Well, this is sort of true, especially the shredding to <1" being expensive part. However, Gold Spotted Oak Borers attack big, old oaks, so planting young oaks is a good thing. They give the insects a home, get some acorns produced, and by the time they get totally Bored in a few decades, you'll probably not be living there anyway. Moreover, if you cut down your infected big oak or willow before the beetles kill it, there's a good chance it will coppice sprout new shoots from its roots and give you another 40 years before the beetles return. And you might be able to control the infestation in the meantime. So don't give up on these trees.
But we're CNPS. The California NATIVE PLANT Society. Why don't we leave the birds to Audubon? Here's the question: what's going to pollinate your native plants? It's not just the butterflies and honeybees. They're the showy ones. Most of the pollination crew consists of tiny native bees, flies, and moths. Give them a place too, even if you can't see them.
Despite me trying to convince you that holed is beautiful, there is that final objection: you're in it for the plants, not to turn the garden you created with your blood, sweat, and hard-earned cash into sustainably produced, locally sourced baby food for the birds. Why would you want to see ragged edges and holed leaves on your ceanothus, let alone your oaks?
As Dr. Tallamy put it, there's a twelve-step program for that. If you take 12 steps back, you won't be able to see the holes. You don't even need a sponsor, just an awareness that little holes are hard to see. As he (the professional entomologist) found out, it's hard for humans to see even a small fraction of the insects the birds routinely find. You're missing most of the damage any way. Don't worry about the rest.
More to the point, this goes along with the idea of planting more natives, more native species rather than just largely clonal cultivars, and planting species from the south as a form of climate migration. In this scenario, you don't need to just migrate the plants, you need to help the insects that eat them, the spiders that eat those insects, and the birds that eat them all, because plants depend on ecosystems, not just gardeners.
So, it looks we've got complicated mission for our gardens: find out what caterpillars from San Diego and Tijuana eat and plant the foods they need, all to support them and their predators. Get your friends and neighbors to follow suit. This is all to keep the birds and the bees and the flowers and the trees in our increasingly simplified landscape, and perhaps to help them move a bit north, too. Oh, and ignore any leaf holes they leave behind. Holed leaves are beautiful, if you see them as part of the process of making more songbirds.