Thursday, April 25, 2013

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

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