Woodpeckers supply services to various forest neighbors

Array of animals, birds make use of what woodpeckers leave behind

Posted: Friday, November 13, 2009

When a woodpecker pounds on your metal downspout early in the morning, it is easy to feel uncharitable. And when one hammered a nice round hole in the side of the house, I was less than pleased.

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Courtesy Of Bob Armstrong
Courtesy Of Bob Armstrong

However, woodpeckers supply important services to other forest beings. They are major makers of cavities: the holes they make for nesting or roosting are used by many other species for shelter or raising babies. Old woodpecker holes are used by bluebirds, tree swallows, chickadees, and nuthatches, for example, as well as flying squirrels, red squirrels, and bats. In some parts of North America, large woodpeckers such as the pileated woodpecker can make cavities big enough for sizable creatures such as marten and raccoons. In some forests, they are considered to be essential for maintaining a diverse community of birds.

Sapsuckers commonly (and other woodpeckers less commonly) make arrays of small wells in tree bark and eat the oozing sap. This creates a food source used by many other forest animals. Uninvited guests include several species of warblers, other woodpeckers, kinglets, sparrows, pine siskins, chickadees and hummingbirds.

Sap wells may be especially important for hummingbirds. Tree sap is similar to flower nectar in sugar content and fluidity. Several species of hummingbirds, including the rufous hummer, are reported to have a close relationship with sapsuckers. The hummers are said to nest commonly near arrays of sapsucker wells and even to follow sapsuckers around as they forage.

Rufous hummers arrive in Juneau in early spring, before there are flowers in bloom or when the only available flowers are those of early blueberry, with its miniscule amounts of nectar in each flower. What do they eat in the early spring? Insects, of course, are an important source of protein to early-arriving adult migrants and, later, to growing chicks. But another important food resource is tree sap from sapsucker wells.

Rufous hummers may even time their northward spring migration to follow that of red-breasted sapsuckers, according to some reports. On their way south in late summer, sapsucker wells are also a good energy source - so good that migrants may even defend a territory around a set of wells for several days before continuing their migration. Competition for access to sap wells can be intense, and as soon as one temporarily territorial hummer leaves to journey on, it may be replaced by another eager eater.

Sap wells also feed a variety of wasps, bees, and other insects. And I once watched a red squirrel enjoying a prolonged sweet lunch while lying flat on a willow branch that was pocked with sap wells. Sapsuckers reportedly have little success in driving away piratical squirrels.

Woodpeckers can also be effective in reducing populations of bark beetles and wood-boring beetles that sometimes wreak havoc on forest trees. One report noted that the average number of spruce bark beetle larvae in the stomachs of American three-toed woodpeckers was over 900-and that was just one meal during the day. They probably have to fill their stomachs several times a day to fuel their activities, so they might eat, say, about 3,000 (or more) larvae in a day. Beetle outbreaks often draw in large numbers of woodpeckers from other areas; in some places, woodpecker density increases as much as 50 times that of a non-outbreak area. If each of those hungry woodpeckers eats 3,000 beetle larvae a day, and there are 10, 20, or 50 times as many woodpeckers as usual, and all those beetle-eaters feed for several weeks - do the math yourself! That's a lot of beetle larvae.

In addition, the drilling and bark-flaking of woodpeckers foraging for beetle larvae exposes uneaten larvae to other predators, parasites, and diseases-all of which reduce beetle numbers still more. So woodpeckers can become beetle control agents both directly and indirectly.

So next time woodpeckers annoy you by drumming on your drain pipes, think twice before dissing the drummers! They do a lot of good!

• Mary F. Willson is a retired professor of ecology.

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