When the weather forecast warns of a looming polar vortex, my first concern as a naturalist is: How will our overwintering songbirds survive this extreme event? We, like our neighbors, heed the public service advisories to keep our two dogs inside. But there is no precautionary measure for the birds that live outdoors 24/7. And even if we could somehow coax a few robins, mockingbirds, a willing junco, or a shivering titmouse into the house, they would be flapping at the windows and French doors, desperate to be released again into the backyard icebox.
Then the biologist in me awakens and posits another question: With the severe weather events associated with climate change predicted to be more common and more extreme, will there be rapid selection among those populations of birds that live multiple years and stay sedentary in our area in favor of those who decide instead to take their chances by migrating farther south in fall? Doing so, after all, might increase their chances of being alive to breed and successfully raise offspring the following spring.
For those birds that do overwinter, the secret of their survival is their ability to store fat and then burn it in times of numbing cold and wind in order to keep their body temperature stoked and at homeostasis. A few species such as chickadees are able to drop their body temperature a few degrees to conserve energy during cold days but for most species it is all about building the fat layer for conditions like those we experienced in late January. When not conserving energy by fluffing their feathers and hiding out of the wind, they seek out what energy-rich fruits remain now that all the insects are dead or dormant and seeds are hard to find.
Once the worst of the polar vortex ends, you might see flocks of American robins roaming about for whatever fruit is still available. And that is where the remarkable Winterberry plant takes center stage.
I am so thankful that a few years ago we planted two female Winterberry bushes in the front yard (and have a female Eastern red cedar offering its berries in the back). Winterberry is a relative of the American Holly tree. It grows neither as stout and tall as the holly, and unlike the holly, it drops its leaves in winter—all the better to make its bright red berries stand out against a snow-lined branch.
Those who care about birds, and that, I will wager, is most people in Cabin John, can always put out suet and seeds in bird feeders to sustain our avian friends. But much better is to go to a local nursery or order on-line at least three Winterberry bushes. You will need at least two because Winterberry, like American Holly and the Eastern Red Cedar, are among the 8% of plants globally that are dioecious—meaning male and female flowers grow on separate plants. So, if you want to have a big crop of bright red berries decking out your female bush or, even better, two female shrubs, a male is needed to be planted nearby. Based on observations made in my walking expeditions in our neighborhood, it is my conclusion that almost every single-family home in our hamlet has room in a sunny spot for three Winterberry bushes. Or if you are more partial to dogwoods or viburnums or the like, you can find a list of other native species to plant and specimens from our local nurseries that produce fruits birds love. The non-Florida dogwoods—such as the pagoda dogwood or silly dogwood, or even red and green-osier dogwoods—produce beautiful fall foliage, brightly colored branches, and offer fruits to birds that are among the most nutritious available. In all these cases you will likely need two; even though dogwoods are not dioecious they don’t self-pollinate, so having a compadre next to it ensures cross-pollination and fruit set.
There are other good choices: Northern bayberry or southern myrtle in warm sunny spots, snowberry, American Beautyberry (not the Japanese version), and red or black chokecherry make birds merry. Even the somewhat scraggly branched staghorn sumac with its dramatic displays of powder-coated fruits (related to the source of sumac for Persian cooking)—we have three of these interesting looking plants in our yard—welcome birds in winter that live on the edge of starvation.
Two days before the recent polar vortex descended from the north, I found myself northwest of Philadelphia driving on a highway past Valley Forge, PA. I didn’t exit, but I did have this thought: how would Washington’s Army have survived the historic cold temperatures we just witnessed this past week? Would there have been a lot more desertions or deaths? And then because I study natural history rather than American history, my thoughts shifted to the question I posed at the beginning: How will the birds of the future survive these extreme weather events?
That is when I came up with the idea of a local Winterberry Army. Many of you know that we are launching a campaign to plant 100 trees this year in honor of the Cabin John Citizens Association’s 100-year anniversary. But what if we have a Winterberry Army, or at least a Brigade, of Cabin John gardeners who take a pledge to plant Winterberry—a male and at least one female—in their yards, or one or more of the other showy shrubs I mentioned above? Why, we could even have streets where one neighbor’s male Winterberry or pagoda dogwood could provide the pollen for their nearest neighbor’s female.
And, at recent Citizen’s Meetings, that “Welcoming sign” we have discussed erecting at the edge of Cabin John? It could read:
Welcome to Cabin John
The Winterberry Capital of the United States
or better yet, if we all joined in and offered a greater diversity of plants:
Welcome to Cabin John
The Winter Bird Fruit Capital of North America
Who is with me?
By Eric Dinerstein
Illustration by Trudy Nicholson