Winter is for the Birds!

Nature // December 27, 2016

You may think that the cold of winter would lay waste to a six-gram bird. However, birds do very well in the cold.  Bird feathers are extremely efficient insulation, and the blood vessels in bird legs utilize an efficient countercurrent heat exchange system that keeps them from freezing, even when they stand on bare ice. In fact, the limiting factor for birds in winter is food.

Most insectivorous birds migrate to warmer regions where they can find invertebrate prey during the northern winter. Some travel to the Southeastern United States, and others go as far as South America. Aquatic birds also migrate, but mostly just one step ahead of ice. For seed-eating (granivorous) birds like song sparrows and cardinals, there is plenty to fuel their furnace, even in the depths of winter. Likewise, woodpeckers can find grubs in sapwood, tiny kinglets, brown creepers, and wrens can feed on dormant invertebrates, and birds of prey feed on rodents and other birds. Wissahickon Valley Park has many year-round resident birds, including quite a few for which our beloved valley might as well be a tropical paradise, full of the necessities of life in all seasons of the year.

The boreal forest, a vast boggy landscape of spruce, fir, and birch trees, runs from the Northern Appalachians to Newfoundland, and west across Central Canada to the Alaska Interior. Breeding birds of the boreal forest, including dark-eyed juncos and white-throated sparrows, arrive in our area in October and depart in early May. They are extremely numerous in the Wissahickon and in wooded backyards and lots. Yellow-bellied sapsuckers also winter in our region, and they are aptly named. Look closely and you can find their parallel rows of holes hammered into the sapwood of trees, especially magnolias and sugar maples, which provide an ample food supply during the cold winter months. Fox sparrows and American tree sparrows are also regular visiting boreal birds, and the Andorra and Houston Meadows are good spots to look for them.

The boreal forest has year-round residents as well. Sometimes when spruce cones and birch cones are scarce, these birds will irrupt south to take advantage of decent substitutes, such as hemlock cones and river birch seeds. This fall has brought a good number of red-breasted nuthatches, purple finches, and black-capped chickadees to the park, joining our resident white-breasted nuthatches, American goldfinches, and Carolina chickadees. Without tracking individual birds, we cannot know whether these birds are breeders in the Appalachians or farther north. Their arrival in Philadelphia is often a harbinger of the irruption of other boreal “finches” like pine siskins, common redpolls, white-winged crossbills, red crossbills, evening grosbeaks, and pine grosbeaks.

There is some indication that this may be an irruption year, so keep a lookout for these birds. They are so dependent on certain trees and shrubs that it is possible to predict their movements. A renowned ecologist even makes a winter finch forecast. The Tree House feeders, conifers of the Andorra Natural Area, the birches of Houston Meadow, hemlocks along Forbidden Drive, and the white pines of the Cresheim Valley are likely places to find winter finches.

The winter has one clear advantage for bird observation: barren trees. During the winter, owls are much easier to find because they concentrate in conifers, and the holes they roost in are not obscured by leaves. Bluebirds wander from the meadow into the woods, and the mighty pileated woodpecker is much easier to track down by its calls without dense foliage. Bundle up and get out this winter. There is still much to see, and the seeing is easier!

By Tony Croasdale, an Environmental Education Planner at Philadelphia Parks & Recreation

Join Tony for weekly guided bird walks every Thursday at 7:30am.  Meet at the Wissahickon Environmental Center for coffee and feeder watching then a walk.  The walks are free and open to all ages. Walks will not be held on holidays or if it rains. Binoculars are available to loan. No registration is required!

Photo: white-breasted nuthatch