The first dawn volley of a yellow-bellied sapsucker on our metal roof is exciting because it signals spring. The twenty-first volley is a little harder to be enthusiastic about, but I forgive them and begin to think “hummingbird.”
Ruby-throated hummingbirds arrive at my house in Vershire, Vermont, by early May, which in the past has always made me vaguely uneasy. At that time of year, what was fueling their flashing aerial combats? Columbine nectar? It seemed impossible, and it was. The answer turned out to be sap from sapsucker holes. In fact, in the north, hummingbirds are found only where these oddball woodpeckers live.
In spite of its name, the sapsucker’s yellow belly is not very noticeable. A better field mark is its red throat and cap, as it is the only member of the woodpecker family to wear red in both places. Sapsuckers breed and spend their summers all across the northern United States and winter as far south as Mexico and the Carribibbean.
But even if you don’t know a yellow-bellied sapsucker from a hole in a tree, you probably know its work. Males and females both drill horizontal bands of small holes into the succulent inner bark of trees and then feed on the nutrient-rich sap that collects in the holes, as well as on insects attracted to the sap. It is these sapsucker “wells” which feed our hummingbirds in early spring before there are flowers. Although I haven’t seen figures on spring sap, one study found that summer sap had a sugar concentration of 16 percent by weight, which is high enough to support hummingbirds without any other sources of nutrients.
In one of those happy confluences of observation and book-learning, I saw this relationship in action one fine summer day. An immature sapsucker was flying clumsily from tree to tree in our yard, taking desultory whacks at tree limbs. There was something endearing and comical about her ineptness that kept my interest. Suddenly I noticed that a hummer was flying in attendance. He perched on nearby branches and followed her closely in four flights before giving up.
Sapsucker wells feed other species also. Sap-drinkers in our area include the hairy woodpecker (downies drill their own sap wells), both species of nuthatches, ruby-crowned kinglet, northern waterthrush, pine siskin, goldfinch, white-crowned sparrow, cardinal, and flying, red, and gray squirrels, plus a number of warblers including the yellow-rumped, black-throated blue, black-throated green, pine, and Cape May. Non-drinking freeloaders such as the crested and least flycatchers, eastern phoebe, robin, and warbling vireo feed on swarms of insects attracted to the sap. Sapsuckers are insect-eaters themselves, especially when feeding fast-growing young, and they devour the larch sawfly, among other pests.
Insect visitors at sapsucker wells in early spring include white-faced hornet queens, who have overwintered and are just emerging from hibernation. Like birds, the queens get energy by drinking the sap, and also come to the wells to catch protein-rich insect prey to feed their young. One observer often finds hornet nests below sapsucker licks perhaps a mutually beneficial arrangement. Such hornets need to keep a sharp eye out for falling objects from above, though a sapsucker sometimes gets tipsy from drinking fermented sap and falls from its tree!
In spring, sapsuckers tap the sap of hemlock, aspen, maple, and elm – all early flowerers. Their summer staples are birches, and they can cause significant damage to economically valuable yellow birch. According to one authority on northeastern woodpeckers, sapsuckers drill most heavily on trees that are already wounded. He found the greatest activity on trees with obvious trunk wounds or fungal conks. However, they also drill, although more lightly, on apparently healthy trees, and it seems probable that this helps maintain a subsequent supply of wounded feeder trees.
This hole-drilling is regretted by people who make their living from harvesting trees, but no one proposes to control it. The sapsucker’s impact on forest health in New England is a complicated story because its feeding and nest excavation benefit so many other species. Chickadees, great crested flycatchers, and nuthatches, for example, sometimes nest in old sapsucker nest holes because they lack don’t have the beak equipment to make good nest holes of their own. Flying squirrels, deer mice, and red squirrels also find them handy housing. These are just a few examples. In fact, the sapsucker’s influence is so widespread that its loss could cause a cascade of changes in the ecosystem.
But back to the metal roof. Why exactly do sapsuckers whack away at roofs, stovepipes, antennas, and metal gates at this time of year? To attract mates, establish territories, and, it would seem, make sure that nearby humans don’t oversleep and miss all the action.