Forest Birds on the Move

By dgross September 30, 2013
Rose-breasted Grosbeak female with fruit Dingel

Female Rose-breasted Grosbeak eating Eleagnus berries by Jake Dingel, PGC

Leaf peepers may not start paying attention to Pennsylvania’s autumn woods until gold hues begin to color woodland hillsides and waterways. Birders, however, notice subtle forest changes¾a shifting of bird life from resident to migrant¾long before fall color splashes the canopy. Birds lend themselves to the fall scenery with many colorful species moving south as the seasons change. Raptors are the most obvious woodland migrants, traveling forest ridge corridors by day to utilize the updrafts and deflected wind currents as they move south. Some of these winged predators, like Broad-winged and Sharp-shinned hawks, show in numbers from late summer, increase to waves of birds by mid-September, and trickle off as fall progresses. Many of the songbirds that forage primarily on arthropods during the nesting season switch to a more frugivorous diet in fall. This knowledge should guide birders to better places to find songbirds on the move.

Blue-headed Vireo by Jake Dingel, PGC

Blue-headed Vireo by Jake Dingel, PGC

The non-soaring forest birds—the songbirds that do not surf ridge top currents or catch rides on rising thermals—must flap their way south with nothing more than a tail-wind boost from favorable winds following cold fronts. Many forest songbirds, including warblers, buntings, tanagers, cuckoos, orioles, vireos, flycatchers, sparrows and most thrushes, travel primarily at night. A few of the advantages of traveling by night may be: avoiding diurnal predators like hawks; maintaining cool body temperatures during lengthy, exhausting flights; and navigating with the help of constellations in the starry sky. Freeing up daytime hours to forage in the light of day is another perk. After a long night of flying, the nocturnal migrants retreat to the forest and its edges to find food and to rest. Not all songbirds travel at night. Swifts, hummingbirds, finches, swallows, crows, Cedar Waxwings, Blue Jays and American Robins migrate during the day. Several of these day travelers such as swallows and swifts feed on the go. They have the aerial agility to easily snatch flying insects from the air around them.

 

Blackpoll Warbler feeding on pokeberry by Jake Dingel, PGC

Blackpoll Warbler feeding on pokeberry by Jake Dingel, PGC

Forest songbirds, diurnal and nocturnal, share the need to refuel along migration routes. Like the swifts and swallows, some birds continue to consume insects and other arthropods, but many forest species also rely on fruit-bearing trees, shrubs and plants along the way to maintain their energy stores, and they especially seek those yielding fatty fruits. Pennsylvania forest land has an abundance of berry-producing flora and identifying some of these important food sources, or recalling where to find them, may lead to good forest birding areas this time of year.

Fall Yellow-rumped (Myrtle) Warbler and poison ivy berries by Jake Dingel, PGC

Fall Yellow-rumped (Myrtle) Warbler and poison ivy berries by Jake Dingel, PGC

Ground foraging migrants such as Hermit Thrush, and American Robin may dine on the brilliant red berries of Jack-in-the-pulpit. Dark-eyed Junco, Fox Sparrow and Northern Flicker find abundant patches of poison ivy which produce clusters of cream-or white-colored berries. The deep purple berries of Virginia creeper attract a host of species including Hermit, Wood, Swainson’s and Grey-cheeked thrushes. These persistent fruits also attract birds and other kinds of wildlife through the winter months.  They can be magnets for Yellow-rumped (Myrtle) Warblers and other songbirds often thought of as only insectivorous.  These clusters of berries also can attract Ruffed Grouse that nibble on them sometimes before the break of day. 

Hermit Thrush by Jake Dingel, PGC

Hermit Thrush by Jake Dingel, PGC

At the shrubby layer are the briers, the prickly brambles of Pennsylvania blackberry that afford migrating birds great protection from predators as they forage for the shriveled berries that ripened earlier in summer. Flowering raspberries provide migrants with fresh juicy berries in late summer and early fall, although they lack the protective thorns. Elderberries, a late August early September fruit, appeal to Red-bellied and Red-headed woodpeckers, Yellow-bellied Sapsuckers, Blue Jay, Gray Catbird and Brown Thrasher, several thrush species, Rose-breasted Grosbeak, Yellow-breasted Chat and Great-crested Flycatchers. These weedy plants are found in edge habitat, young forests habitat and in disturbed areas of mature forests.

Wild grapes are native vines that sometimes grow into dense, jungle-like tangles, especially along rivers and wooded hillsides. Grapes attract a broad range of birds including American Robins, Eastern Bluebirds and other thrushes, Brown Thrashers, Northern Flickers, Baltimore Orioles, Scarlet Tanagers, Red-eyed, Philadelphia and Warbling vireos, Yellow-breasted Chat, American Redstart and Pine Warbler. Greenbrier is another vine. The tiny blue-black berries of common greenbrier are sought after by White-throated Sparrow, Cedar Waxwing, Gray Catbird and several thrushes. These deep tangles also can hide Northern Bobwhites in the southern counties.

Although its distribution is somewhat patchy in Pennsylvania, occurring in open woods, the late-summer berries of northern bayberry attracts a variety of migrating songbirds including Eastern Towhee, Carolina Wren, Scarlet Tanager. Yellow-rumped Warblers feed on the wax-covered fruit as well. During migration, Yellow-rumped warblers also visit sumac stands. Many other forest birds feed on the drupes of several sumac species including Pine Warbler, Northern Flicker, Red-headed Woodpecker, Pileated Woodpecker, Red-eyed Vireo, Purple Finch, Brown Thrasher, Hermit and Wood thrush, and Northern Mockingbird.

The humble pokeberry also attracts many birds.  The purple berries area  magnet for catbirds, thrushes, warblers, and sparrows.  They can be attractive food even when dried on the stalk.  Migrating fall warblers gobble up pokeberries on their way south. 

Black-throated Green Warbler feeding on pokeberries by Jake Dingel, PGC

Black-throated Green Warbler feeding on pokeberries by Jake Dingel, PGC

Dogwood is another fruit-producing woody shrub and tree at the mid-level and two species of dogwood are particularly important fall bird foods. The globular, blue-black berries of alternate-leaf dogwood ripen in October and attract a lot of birds including thrushes, woodpeckers, vireos, Great Crested Flycatchers and White-throated Sparrows. Flowering dogwood, with its bright red clusters of berries, is another great shrub to look for when birding. Because of their showy blossoms in spring, this shrub is often memorable and easy to relocate come fall. In addition, it often grows along dry ridges and near forest and woodland edges. Some of the birds naturally attracted to flowering dogwood are Yellow-rumped Warbler, Pine Warbler, Summer Tanager, Rose-breasted Grosbeak, Evening Grosbeak, Purple Finch, Grey-cheeked Thrush, Wood Thrush, Eastern Kingbird, Song Sparrow and White-throated Sparrow. Many of the same birds also forage on the Viburnum species more often found in the woods. This genus of wildlife-valuable shrubs includes arrow-wood, hobblebush, nannyberry, dockmackie (maple-leafed viburnum), and witherod.

Northern Flicker on Staghorn Sumac by Jake Dingel, PGC

Northern Flicker on Staghorn Sumac by Jake Dingel, PGC

Common along the dry slopes and ridge tops across the southern half of Pennsylvania is the black gum tree. However, this tree reaches its greatest heights and girths when it occurs in the moist soil of stream bottoms. The black gum produces a dark blue berry that ripens in autumn and is a good food source for forest birds. Veery, Scarlet Tanager, Rose-breasted Grosbeak, Wood Thrushes and Yellow-bellied Sapsuckers are just a few of the birds that readily forage black gum drupes in fall. American mountain ash is another tree to look for. It often grows in disturbed areas at the forest edge and around swamps and bogs. The large clusters of orange-red berries are actually pomes which ripen in October and remain into winter. Other fall finds for birders may include a hawthorn trees, crab apple and common hackberry.

For more information about Pennsylvania bird plants, see:

www.pabirdplants.org/

plants.usda.gov/

Common Trees of Pennsylvania, Department of Conservation & Natural Resources, Bureau of Forestry

 

Story by Kathy Korber, PGC

Photos generously contributed by Jake Dingel of the PGC