Percussion Concussion

by Tom Lewanski

You may be jolted awake one morning soon by an explosive racket that sounds something like a machine gun going off in the next room. You’ll wake up and smile — the yellow-bellied sapsuckers (Sphyrapicus varius) have returned! OK, I just wrote that, walked outside, and heard the first sapsucker of the year, so they are right on schedule. They are less common in the urban core, but if they are present, you’ll know it! The hammering is done by males, advertising their territories and calling for a mate. To best accomplish this, it helps to be loud, and they have a knack for finding the most resonant objects out there. In the natural world, that would be hollow or dead branches that have great resonance. But with the arrival of human technology, sapsuckers have taken advantage of a whole new element they had no access to before – metal! Not being a particularly shock-absorbing substance, one only wonders what hammering on a metal sign or chimney vent does to the brains of these birds, but they seem unimpaired. Aside from the generally loud volume, their signature drumming is easy to identify as it starts out fast then slows at the end.

Sapsuckers are an interesting woodpecker in other regards. While most woodpeckers drill holes in trees to obtain the insect larvae within, sapsuckers drill holes to obtain, you guessed it, tree sap! Not all trees are created equally, however, and they do have preferences. Paper birch, with sucrose concentrations of 20% or more, is one of their favorite species. American basswood is also favored, but they will sample many species including American elm, juneberry and even pine species. They maintain the holes to keep the sap flowing and return to them for frequent sips. As the sap dribbles down the side of the tree, ants and other insects are attracted. It was once thought that sapsuckers drill holes for the purpose of attracting and eating insects. While the birds may eat an occasional insect at a sapwell, they drill the holes specifically to drink the sweet sap and have even been seen flicking insects off the sapwells.

It is interesting to note the different drilling pattern that sapsuckers use on different tree species. In paper birch, for example, they concentrate the sapwells in a few areas of the tree, creating large grids of close, evenly spaced holes, that may extend two feet vertically and girdle a branch or trunk. In contrast, rows of drill holes in basswood trees are spaced several inches apart, and in other species more scattered still. The sapwells are used all season, and sometimes repeatedly year after year. Very extensive use can damage or kill a tree, but more often the damage is minor and trees recover.

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