Sapsuckers and sap flow

What: Last week, I was out checking the bees with Zac and Sophia and we noticed that the boxelder looked like it had wet its pants. A few days earlier, Clay had spotted an odd ball woodpecker in our backyard and I thought from a quick glimpse it may have been a sapsucker. When we inspected the "wet spots" on the boxelder, sure enough there were all sorts of little drill holes. We licked the bark and it was delicious.



There are a lot of origin stories about the human discovery of maple sugaring. I'll bet almost all of them are false and created many generations after humans were utilizing syrup. I've got three bets for how humans discovered sugaring:

1. Red Squirrels: I've watched red squirrels chew little notches in branches of sugar and red maples. I've also watched them return and lick off the sap from bark later.
2. Sapsuckers: Water can be hard to come by in the winter. Curiosity, particulalry when there's a need for something, runs high in humans. My first inclination when I saw the drill holes and wet bark was to wonder what the sapsucker was after. My second inclination was to taste the sap. I was rewarded with a delicious treat.
3. Broken branches: Silver maples and boxelders both grow along floodplains. Winter can be rough on trees and without the metabolic activity to heal wounds, exposed wound sites will "bleed" once the sap starts flowing. Early in the sugaring season, when temperatures still drop well below freezing at night, any sap that might flow out of a broken branch can freeze into a sapsicle. The water freezes first and the outer coat is extra sweet. Kids love to suck on icicles and I'll be it was a kid that first discovered these sweet treats. 

I've kept an informal list over the years of species that I've seen sapsuckers tapping. The list this year includes: Black walnut, Red oak, Boxelder, Silver maple, Hemlock, Bitternut hickory, White pine, Norway spruce, Black cherry, and Paper birch.

black walnut with drill holes from sapsucker

Yellow bellied sapsucker

Male yellow-bellied sapsucker (females lack the red "beard")

What: One of my students found a yellow-bellied sapsucker (Sphyrapicus varius) that had died near her house (no sign of predation, perhaps flew into a window). The next day we got to watch a sapsucker drilling holes in a bitternut hickory (Carya cordiformis) and licking out the sap. I propped open the bird's mouth with an elderberry twig to show the bristles that line the tongue. Birds can't "suck" like we can from a straw, so having the hairs allows the woodpecker to lick up much more sap than a smooth tongue would be able to. The hairs work via capillary action, which is the ability of water and other liquids to overcome the force of gravity via intermolecular attractive forces to solids. This can be seen readily by holding the tip of a napkin in water and watching the water travel up the napkin. So all that surface area acts as a magnet of sorts and the little birdie can lap up even more liquid.

Ecological notes: Sapsuckers make distinctive horizontal rows of sapwells. It's interesting to note that we had tapped a bitternut hickory and hadn't gotten any flow. The sapsucker showed up just as the sap started dripping into our buckets. While the sapsuckers miss the better flow of maples, they have been recorded utilizing over a thousand different species, so there's plenty for them to go after.

I was also impressed by the incredible sharpness of the claws. I could easily perch the bird on my finger from just one of its claws. It's feet kept getting caught on everything because they were so sharp. Must be an adaptation for gripping a tree as the bird fiercely bangs its head against it while making its sapwells.

Where: Rock Point, Burlington