Signs of Winter 4: The Downy Woodpecker

(The following is an excerpt from a species page that will soon be published out on the Virtual Nature Trail. Information for this page was gathered in part by Ms. Brittany Hydock for her Spring 2015 Honors Biology 22o class at Penn State New Kensington).

Photo by K.C.Agar, Flickr

The downy woodpecker (Picoides pubescens) is a small (five to six inches long) woodpecker that is quite common not only in Western Pennsylvania but also across the continental United Sates and up into Canada and Alaska. Its distinctive black and white, checkered plumage and white breast match the coloring of the larger, slightly less common, hairy woodpecker (which is about one third again larger than the downy). Male downy woodpeckers have a prominent red patch on the backs of their heads but are, in size and other coloring, identical to the females. These active birds are found in a wide variety of forested habitats. They prefer to live in deciduous forests and especially like to feed on and nest in elms and birches that have been weakened by fungal diseases or age. Dead trees and trees with physical deformities (bent trunks, knobby growths, or patterns of holes) are preferentially visited by foraging downy woodpeckers.

Downy woodpeckers primarily eat insects but also consume seeds and a wide variety of berries.  Downy woodpeckers are frequent visitors at backyard bird feeders and are especially fond of black oil sunflower seeds. They also avidly feed on poison ivy berries and are one of the avian agents responsible for this noxious plant’s extensive occurrence and rapid rates of spread. Preferential feeding on softened trees saves the downy woodpecker a great deal of energy when it drills into the bark and heart wood searching for insects. Chemical cues from the afflicted tree along with visual recognition of scars, holes, missing bark and odd trunk curvatures attract these woodpeckers to these more easily excavated (and often more insect rich!) trees.

Photo by D. Brezinski, USFWS (Public Domain)

In the summer many of the insects taken by the downy woodpecker are on the surface of the tree bark, and the foraging downy simply utilizes its long, sticky tongue to snatch up these freely roving insects. Little hammering and drilling for food, then, is required. In cooler weather, or when insects are not abundant on the surface of the trees, a downy will typically work its way up a tree by a combination of short jumps and fluttering flights going first to any visual, surface deformities on the bark. The downy will peck at the bark in an attempt to stimulate any subsurface insects to begin to move about. The downy then use its excellent sense of hearing to locate these moving insects and rapidly drill a circular hole in the bark in order to capture them.

Female downy woodpeckers tend to forage on the lower, larger branches and trunks of trees while the males tend to forage higher in the canopy on the smaller branches and more slender sections of the trunk. These foraging preferences very effectively separate the feeding habitats of two genders and both broadens their individual feeding habitats and reduces potential intraspecific competition for food.

In the winter downy woodpeckers join with a variety of small song birds to form mixed flocks. Species included in these flocks include chickadees, titmice, white-breasted nuthatches, kinglets, and brown creepers. These flocks may seem at first glance to be detrimental to the survival of these birds (all food sources found by members of the flock are shared among all of the individuals) but the increased percentage of food sources found and the increased protection against and awareness of predators makes these associations energetically quite beneficial to all individuals. Interestingly, female downy woodpeckers continue to be members of somewhat smaller mixed flocks throughout the year. Males, though, only participate in these flocks in the winter.

Photo by D. Scranton, Flickr

The breeding season begins in March with the onset of male to male conflicts and male to female bonding. The male to male conflicts are typically quite ritualized with a stylized bill-waving and head movement “dance.” Once the males and females pair up they engage in a drumming display that expresses many aspects of their developing relationship. Drumming is used to call a distant mate, to locate and display possible nest sites, to defend territory, to strengthen the pair bond, and to indicate willingness to copulate.

Both the male and the female downy woodpeckers search for the most optimal nest site. Trees that are old or even dead, or which have extensive fungal infections are most ideal. Trees that already have holes are also preferentially selected. The small size of the downy woodpecker enables them to utilize relatively small limbs for the nest cavity. The cavity itself can be quite small (as small, in fact as twelve square centimeters). The small size of these nesting cavities reduces the possibility of another, larger bird attempting to take over the site. Tops of trees and bases of trees are both potential sites of increased predator risks, so the downy woodpeckers typically nest in the middle levels of their selected trees.

If the woodpeckers are excavating a new nesting hole the process may take up to three weeks of exhaustive work. The end nesting cavity is typically an inch to an inch and half in diameter and six to twelve inches deep. The floor of the nesting cavity is then lined with wood chips and is ready for the eggs.

The female lays three to eight, white eggs in the nest. The eggs are one inch long and a half an inch wide. The eggs are incubated for twelve days. The nestlings are fed regurgitated materials by both parents for four or five days and then begin to consume entire insects that the parents bring to the nest. Nestlings grow and develop for eighteen to twenty-one days and then, as the nest cavity gets more and more crowded, begin to emerge out onto their nesting tree. Short, practice fledgling flights take them around their nesting tree. During this period they always return to their nest cavity. They then begin to follow their parents on their foraging flights and eventually will break away from parental influence and become independent. Downy woodpeckers have one clutch per breeding season.

The life span of a downy woodpecker is quite short in the wild. They live on average for four or five years, but half of the birds will die before they are two years old. Their small size makes them vulnerable to predators (like the sharp-shinned hawk or the red-tailed hawk). Nest predators (like the black rat snake) also take a significant percentage of nestlings.