Nature Notes

This fall, have you noticed flocks of birds descending from trees, sky, and wires to feast on bushes or trees loaded with berries? It’s fun to see both migrating birds and our familiar year-round resident birds taking advantage of this natural bounty. There’s more of it than you might imagine.

Eastern bluebirds (Sialia sialis), known as “everyone’s favorite birds,” eat insects year-round, but they also dine on fruit from late summer through winter. In fall, a small flock of bluebirds can strip the bright red berries from a flowering dogwood tree (Benthamidia florida, Cornus florida) in a day or so. Decades ago, our bluebirds typically flew south for the winter. Now we often spot them in winter. Many stick around, thanks to milder winters, the wild fruit in our woods, fields, and gardens, and the “bluebird boxes” that have been widely installed for them to nest in.

What makes dogwood berries popular with bluebirds and other wildlife? Flowering dogwood berries are a high-energy food for wildlife, with a 24-percent fat content (as well as calcium). Fat from fruit supplies energy for migration and for bodily warmth in the cold.

Not surprisingly, bluebirds and many other birds also go to wild dogwood shrubs (family Cornaceae) for berries. Look for these shrubs along edges of trails, fields, and woods. Find red osier dogwood (Swida sericea, Cornus stolonifera) in wetlands, with white berries on waxy, bright-red stems in winter. Silky dogwood (Swida amomum, Cornus amomum), also called swamp dogwood or kinnikinnik, grows on the banks of streams, swamps, lakes. It has dark blue berries on maroon twigs. Gray dogwood (Swida racemosa, Cornus racemosa) bears white berries with a 39-percent fat content in late summer. Round-leaved dogwood (Swida rugosa, Cornus rugosa), at forest edges, produces blue berries.

Have you seen large flocks of migrating blackbirds laying siege to dogwoods and other fruit-laden shrubs? Such flocks typically contain European starlings (Sturnus vulgaris) and/or common grackles (Quiscalus quiscula). A few cowbirds, red-wing blackbirds, and even robins might be included. The starlings especially like insects, berries, and crabapples (small, sour apples less than 2 inches wide). Grackles go for both seeds and berries.

Birds consume the most nutritious berries first. You might notice that not all berries in the woods and fields have been eaten yet. The oval red berries of spicebush (Lindera benzoin), with a 33-percent fat content, disappeared quickly in early September, but bright red berries of winterberry (Ilex verticillata) remain into winter. People sometimes use the dark red sumac berries in summer to make a lemonade-like drink known as “sumac-ade,” yet birds leave most sumac berries until late winter. Sumac berries (Rhus hirta and Rhus glabra) are low in fat but contain vitamins A and C.

As yellow-rumped warblers (“yellow rumps”; Setophaga coronata, Dendroica coronata) migrate through our area at this time of year, they seek out the small white berries on poison ivy vines (Toxicodendron radicans, Rhus radicans). Poison ivy grows throughout most of eastern North America, so birds can feast on the berries along their southward journey. Some 60 species of birds feed on poison ivy berries without harm. Competitors for poison ivy berries include our northern flickers, game birds such as ruffed grouse and ring-necked pheasants, and even white-tailed deer. Yellow-rumps and woodpeckers also like the dark blue berries of Virginia creeper (Parthenocissus quinquefolia), with a 23-percent fat content. This vine climbs up tree trunks, as poison ivy does.

The digestive system of yellow rumps is specialized to digest wax, so these birds can enjoy the 50-percent fat content of bayberries (Morella caroliniensis, Myrica pensylvanica). (In colonial times, wax from bayberries was used to make candles.) Some yellow rumps linger on Cape Cod, where bayberry is more common than it is in our area.

Birds also go for the blue or purple berries of pokeweed (Phytolacca americana), as well as maple-leaf viburnum (Viburnum acerifolium), which is common in local woods, and other viburnums. Cedar waxwings (Bombycilla cedrorum) are fruit eaters named for their habit of hanging around red cedars (Juniperus virginiana) and juniper (Juniperus communis) to eat the waxy blue berry-like seed cones.

American robins (Turdus migratorius) forage for worms and insects on our lawns in spring to get protein needed for reproduction. Then robins seem to disappear in fall and winter, but many stay. They retreat to the woods and switch to a diet of wild fruit. Crabapples are a favorite, especially when they’ve been softened by freezing and thawing. Some robins go south, eating wild fruit along the way. Other robins actually come from farther north to winter here.

Non-native plants in our landscape attract fruit-eating birds, even though their berries tend to be low in nutritional value. Mockingbirds (Mimus polyglottos) typically migrate south, but individual birds sometimes stay if they can feed on the small red berries from a large (non-native) multiflora rose bush (Rosa multiflora). Other non-native fall berry producers include Asian bittersweet (Celastrus orbiculatus), autumn olive (Elaeagnus umbellata), burning bush (Euonymus alatus), and privet shrubs (Ligustrum species).

Other birds get through the winter on seeds they find in the wild and in feeders. Seed eaters typically have longer digestive tracts, and/or longer digestive times, than fruit eaters. Some birds even forage for nuts (which are big seeds) in fall and winter. Don’t be surprised to find blue jays (Cyanocitta cristata), wild turkeys (Meleagris gallopavo), and grackles competing for acorns with chipmunks, squirrels, deer, and other mammals.

As winter approaches, think about the challenge of winter survival for our wild creatures, including birds. This Thanksgiving, be glad for the abundant wild fruits and seeds that feed them in our natural environment.