BY KIERAN LINDSEY, PhD
You know how there’s always that last bit of liquid in the glass, just a few drops, that’s resistant to lift-off no matter how many times you re-position the straw or how much suction force you apply? Well, Yellow-bellied Sapsuckers (Sphyrapicus varius) solved this physics problem over 10,000 years ago. Turns out, the solution to this conundrum isn’t a chalkboard and a large brain. All you need is a fuzzy tongue.
Truth be told, physicists did eventually figure out the basic premise for why a textured tongue is a better slurper than a plastic straw. The first person known to have recorded observations of capillary action (aka wicking) was Leonardo da Vinci, in the late 15th century. A former student of Galileo by the name of Niccolò Aggiunti apparently took a stab at explaining the process in the early 1600s, and experimental studies were attempted over the next two hundred years.
Not until the Young-Laplace equation was derived in 1805, however, did the concept of surface tension arise and take hold. Twenty-five years later, German mathematician Carl Friedrich Gauss reported on the boundary conditions governing capillary motion at the liquid-solid interface (i.e., where tongue meets sap).
All the while, Sapsuckers da Nord America (red-naped, red-breasted, Williamson’s, and yellow-bellied) kept on French kissing timber, lapping up tree juice with those shaggy oral sponges. Thankfully, science, physics, and mathematics don’t require H. sapiens and avians to know how they work to do their job . I mean, it’s always nice to feel understood but that’s a perk, not a prerequisite (thankfully).
The lingual muscle needn’t be lengthy for the mop to do its work. Sapsucker tongues are far shorter than those employed by other members of the Picidae family, some of which are so elongated they wrap around the skull because the mouth isn’t a large enough garage in which to park it. Then again, sap flows through the xylem and phloem layers of the tree trunk, just below the bark, so the swab doesn’t need to stretch all that far to hit the spot.
First comes chipping, THEN comes sipping. That bottle-brush sapsuckers carry around between the upper and lower mandibles of their beak isn’t the only specialized instrument in their tool belt. The bill itself is quite a handy chisel, useful for making a home AND dinner.
This sunny-tummied bird forges two kinds of holes for harvesting sap — shallow and rectangular, or deep and spherical — organized in rows. The boxy gouges provide quick gratification from the closer phloem layer but require constant upkeep. It takes more time and effort to drill into the xylem layer but doing so creates longer-lasting reservoirs of sweeter liquid. The resulting sapwells are kind of like the spout-and-bucket system used for harvesting maple sap except the “pail” is on the inside. Red maple and paper birch are favorite flavors, in addition to alder, hickory, poplar, serviceberry, and willow, as well as fir, pine, and spruce.
That’s a lot of wood to whack, using yet another implement in the sapsucker arsenal — a head that doubles as a hammer. Just to be clear, we’re not talking about a mildly peckish drubbing. The average woodpecker bangs its beak against the solid object of interest 20 times per second at a velocity of 15 mph. That’s the equivalent of revving your noggin’s engine into the rocket-ship red-zone of 26,000 mph, then slamming to a complete stop every second more than 12,000 times a day, subjecting the gray matter inside to a force of 1,200G. Humans generally suffer a concussion at 80 to 100G. For comparison, colliding NFL players experience a force of between 100 to 150G, albeit wearing a highly engineered helmet.
I don’t know how the term “yellow-bellied” came to personify a cowardly wimp but surely it couldn’t have been coined by anyone who’d ever seen a sapsucker at work.
The smithies who fabricate these taps aren’t the exclusive end users. Insects, hummingbirds, warblers, bats, and opossums are but a few of the patrons who belly up to the bar for a free shot when the proprietor is away.
It’s important to note that all this imbibing can have negative consequences. Intensive feeding can damage or even kill the tree, especially if the rows of holes result in girdling, preventing the tree from gaining access to the water and nutrients it needs to live. Deciduous trees, including birch and maple, are more vulnerable to impairment than conifers.
Although sap is the go-to go-juice, even sapsuckers and hummingbirds can’t live on sugar alone. Besides, who doesn’t enjoy a crunchy snack to accompany a refreshing beverage? During the nesting and chick-rearing season, insects account for about 50% of the adult diet, and a higher percent of the nestlings’ intake. Preferred protein sources include beetles, ants, damsel- and dragonflies, butterflies, moths, and caterpillars. In spring, when trees and insects are still waking up from the long winter’s nap, sapsuckers supplement their diet with berries and buds.
One thing’s for certain, a syrup-sweet life is a life in near constant motion… and on that note, it’s time to fly.
See ya, sapsucker!
