Non-vocal communication between woodpeckers has become apparent in the last week or so — hairy woodpeckers have started to hammer out bursts of steady staccato drum beats on nearby trees. Both male and female woodpeckers drum year round, but they do so most intensively from January to May, especially during the courtship and early nesting seasons which begin in March. Woodpeckers drum for a variety of reasons: defending territory, attracting a mate, maintaining contact with a mate, signaling readiness for copulation and summoning a mate from a distance. Woodpecker pairs also engage in duet drumming, which is thought to play a role in nest site selection and in promoting and maintaining the bond between mates.
If you are hearing but not seeing a woodpecker drumming, it is possible to identify the species by the pattern and pace of its drumming. According to ornithologist David Sibley, the drum of the Hairy Woodpecker is extremely fast and buzzing, with at least 25 taps per second, but has long pauses of 20 seconds or more between drums. The Downy Woodpecker drums at a slower rate, only about 15 taps per second, and drums frequently, often with pauses of only a few seconds between each drum. (Photo is of a female Hairy Woodpecker.)
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When their offspring are very young, Hairy Woodpeckers feed them by regurgitation. As the nestlings mature, the parents bring food back to the nest. Most species of birds (85%) engage in bi-parental care, where the male and female contribute equally to feeding and guarding their young. Often the male does more of the food gathering and the female more of the brooding.
In some of these species the male and female both brood as well as gather food. Hairy Woodpecker parents share these duties equally for the month that their young remain in their cavity nest. They both brood their young, with males typically getting night duty, and both gather food for their nestlings. Lawrence Kilham, a New Hampshire MD and ornithologist, found that male Hairy Woodpeckers foraged farther from the nest, made fewer feeding visits, and brought larger prey to nestlings, whereas females remained closer and fed young three to four times as frequently as males. (Photo: female Hairy Woodpecker arriving with arachnid food, male about to depart. Thanks to Suzanne Weinberg for photo op.)
Woodpeckers have begun their courtship drumming and they continue to excavate trees for food. Both of these activities involve a woodpecker’s head striking a tree’s surface at speeds up to 13 – 15 mph, and continuing to do so at over 100 strokes per minute. To sustain this kind of blow against a tree, woodpeckers have a number of skull adaptations, including strong yet lightweight skulls and bills, a network of bony supports within their skull, extra calcification of the portion of the skull nearest the tip of the bill, cushioning cartilage joining the bones between the skull and the beak, shock-absorbing neck muscles and a brain that is packed very tightly into the brain cavity.
A woodpecker’s brain, however, isn’t the only part of its anatomy that is adapted for drilling wood. A woodpecker’s nostrils are narrow slits (not circular, as in many birds) and are covered with bristly feathers that prevent wood chips and dust from entering them. Special cells on the end of its bill are constantly replacing material lost due to drilling. This keeps the chisel-pointed bill strong and resilient, while allowing it to be sharpened with every blow. And finally, less than a second before a woodpecker’s bill contacts wood, a thickened nictitating membrane closes over its eyes, protecting them from flying wood chips. (Photo: male hairy woodpecker)
There are two main ways that woodpeckers and occasionally other birds remove bark in search of insects beneath it. One is bark sloughing, where a bird pries off the entire dead layer of bark on a tree (see NC post on 12/5/14). Another method of locating insect larvae that both woodpeckers and nuthatches employ is the removal of individual scales of bark. This is referred to as bark scaling. The pictured hairy woodpecker has removed much of the bark of a dead eastern hemlock using this method.
In winter, dehydration can be as much as or more of a threat than starvation for birds. At this time of year, they often get their water supply from melting icicles and puddles. When it is severely cold and there is no available water, they eat snow, as this Hairy Woodpecker is doing. It takes a lot more energy for birds to thaw snow and for their bodies to bring the freezing temperature of the snow to their body temperature (roughly 102°F.) than when they take a drink of water. Water is also key to keeping a bird warm in the winter, as it is used to preen, or clean and realign, their feathers so that they can maintain pockets of air next to the bird’s skin that retain the birds’ body heat.
While access to water is essential, there can be too much of a good thing, especially in freezing temperatures. If you have a heated bird bath, it’s a good idea to put stones in it or sticks across it to prevent the birds from immersing themselves in very cold weather.