Marauding hoards have been descending on Maine in recent weeks. Luckily for us, they are after just one thing—small fruits! No bigger than a robin, they are clad in feathers. Indeed the largest numbers of them have been American robins, with some cedar waxwings, Bohemian waxwings, European starlings, and pine grosbeaks mixed in.

In midwinter it is not uncommon nowadays here in Maine to have flocks of robins and waxwings appear wherever there are ornamental crabapple trees still laden with their small fruits. Populations of robins and waxwings in North America are stable or increasing over the last 40-50 years, perhaps in part because of the increased availability of ornamental fruit trees that help birds survive through the winter. Of course these bird species survived for millennia by eating native, naturally occurring fruits; in fact the cedar waxwing is so named because of its original habit of eating the fruits of native types of cedar (also known as juniper).

Robins and waxwings consume protein-rich insects and, in the case of robins, earthworms, during the summer months, so it is rather amazing that they can switch to eating in winter a diet based on sugars—like a kid in a candy shop, every day! Apparently they can also get some protein in the winter by eating the buds of certain trees as well as finding wintering insects.

But mostly they just try to find crabapple trees that are richly endowed with fruits and swallow whole as many of the fruits as they can gobble up in one sitting. Birds will sometimes fly down to a fruit tree from the top of a nearby tree, eat a number of fruits, then fly back up to the higher tree where they can watch for hawks or other dangers while they digest what they’ve eaten. If nothing bothers them, they may go back down and get more. It is amazing how the number of birds feeding on a set of fruit trees can grow over a number of days, as passing flocks detect other fruit-eating birds and come to check out what they are feeding on.

Some of our summer birds also switch, at least partly, to a fruit diet after they head south for the winter. Yellow-rumped warblers are one species that occurs along coastal Maine in winter in small numbers. These birds are thought to largely subsist on the hard waxy fruits of bayberry.

The eastern kingbird, a flycatcher common here in Maine during the summer that is hard to imagine eating anything other than insects, actually becomes an avid consumer of berries on their South American wintering grounds. The red-eyed vireo (the “preacher bird’), a common summer resident of deciduous forests in Maine and one that is often seen eating caterpillars during the summer, are known to regularly feed on berries during fall migration as they try to bulk up for the long journey to South America for the winter.

These fruit-eating birds, wherever they are, providing a major ecological service. Swallowing the fruits whole means that the hard seeds have to eventually come out the other end of the bird. That means that seeds of various trees and shrubs are scattered around the landscape (with fertilizer!) as the birds eat the fruits and then fly away, later depositing the seeds some distance from the original tree—the original Johnny Appleseed!

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists, and author of “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a statewide nonprofit membership organization working to protect the nature of Maine. Both are widely published natural history writers and coauthors of the book, “Maine’s Favorite Birds.”