A Short Note On Sapsucker Ecologies

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About 10 minutes North of Orangeville, along the fence line of Bruce Trail at Dunby rd, there are a couple of American Mountain Ash (Sorbus americana) trees. These trees are related to the other Sorbus species from around the world, but this one is native to the area. Shorter trees, compound leaves, bright red fruit all help to identify these trees in the warmer months. But in the Winter and early Spring when the leaves and fruit have fallen, the bark becomes a great focal point for local ecologies.
The rows of small holes of various age and sizes freckle the bark like oversized lenticels. It kind of looks like a canker or fungal infection, but it’s not. It is actually the work of a meticulous and skilled member of the Picidae (Woodpecker) family; the Yellow-bellied Sapsucker (Sphyrapicus varius – from here out referred to by their banding code of YBSA), a bird which I have not seen that often, but I have come across their sign quite a bit.

YBSA, with a total length of 21.5 cm (8½ in) and a wing span of 40.6 cm (16 in), and weighing in at 50 g (1.8 0z) is the second smallest woodpecker native to our area. The only native woodpecker who is smaller would be the Downy Woodpecker (Picoides pubescens), and as with most woodpeckers that I am aware of, the YBSA catches flying insects while on the wing, an activity sometimes called “hawking” as well as gleans insects from the bark of trees.

This is where it gets kind of interesting through. Sapsuckers, including the 3 western species: the Red-breasted (S. ruber), Red-naped (S. nuchalis) Williamson’s (S. thyroideus) and the eastern Yellow-bellies, have a skill-set which I don’t think is shared among other woodpeckers. They tap various trees by drilling little pits with their bills which slowly fill with sap (the pits are collectively called sap wells).

There also seems to be a pattern to the order in which the YBSAs drill the wells. They start their work in the pre-dawn hours with horizontal lines (primary bands) of these small pits, drilling in an exploratory fashion. These primary bands are shallow and produce sap quickly, and will likely be visited multiple times a day in the Spring when the sap is really flowing. These primary bands are found most commonly and across a wide array of woody perennial species as it is an exploratory activity, when the YBSA is looking for good food sources. If the YBSA finds a seam of good sap they begin tapping vertically above the primary bands, with holes above holes above holes, eventually dotting the trunk as seen in the images.

As they excavate these wells they also consume the cambium and phloem layers exposed by the drilling. Then, while waiting for the pits to fill they may fly off and explore a new tree and continue tapping holes looking for good flow. When they return to their original wells to lap up the sap with their long brush-like tongues, often those first sap wells have also been visited by insects which may still be there for the Sapsuckers to consume along with their sweet sap.

John Eastman in his book Birds of Forest, Yard and Thicket (Stackpole Books, 1997) lists some of the insects YBSA feed on

“carpenter ants, crane flies, may flies, beetles, moths (including destructive spruce budworms and forest tent caterpillars), yellow jackets and hornets…

…[s]ome twenty-two families of insects feed at sap wells wood gnats, Aulacigaster flies, flesh flies, muscid flies, blow flies, and pomace or fruit flies. Such butterflies as mourning cloaks and Compton tortoise shells, nocturnal moths, ants, bumblebees, and wasps all come to sap wells.”

Not only do insects visit the wells but so do some 35 other birds species. Some are there to feed on the sap, some are there to feed on the insects who are feeding on the sap. One bird which comes to the wells is the Ruby-throated Hummingbird (Archilochus colubris) in search of that sweet nutritious flow which can fill the gap until the nectar filled flowers bloom in abundance. This isn’t always a reliable site of sustenance for the Ruby-throat though. I watched a dogfight between the two species in Algonquin Park at the Wildlife Research Station in August of 2020 up high in the canopy of which trees I cannot recall. It seemed like that YBSA wasn’t into sharing the wells that day. Some mammals are also known to visit the occasional sap well of a YBSA, such as Red Squirrels (Tamiasciurus hudsonicus), Porcupines (Erethizon dorsatum), and Bats (Vespertilionidae family).

Sap wells on Eastern Hemlock (Tsuga canadensis) in Algonquin Park.

It’s not just about the sap wells the YBSA woodpecker has dietary preferences which change as the seasons do. In breeding season, it’s mostly the insects, during the Autumn they also include berries and fruits such as Cherry (Prunus spp.), Dogwood (Cornus spp.), Virginia-creeper (Parthenocissus quinquefolia), Hackberry (Celtis occidentalis), Elderberry (Sambucus canadensis), and many more.

Throughout the year except for breeding season, the sap wells are the dominant food source for the YBSAs. I have read of many species of trees and shrubs which the YBSA likes to feed on and this list is pretty extensive. In the book The Birders Handbook by Ehrlich, Dobkin and Wheye (Simon and Shuster, 1988) the authors write “Sap taken from 246 native trees”. A few I have found in my research or observations are Paper Birch (Betula papyrifera), Sugar Maple (Acer saccharum), Serviceberry (Amelanchier spp.), Large-toothed Aspen (Populus grandidentata), American Mountain Ash. I have also seen sap wells on Eastern Hemlock (Tsuga candensis) and Scots Pine (Pinus sylvestris) which just sounds gross and overly sticky to me. How does the YBSA clean their bill?

As I have been learning about YBSAs I keep developing new questions. Some of which are included below:

  • What draws them to the sap? Sugars or nutrients or flavour or something else entirely?
  • I read that they feed insects to their young. How do the young get a taste for sap? Do they feed the young sap soaked insects?
  • Why isn’t this sap feeding habit more widespread across more woodpecker species?
  • How will tree migrations caused by climate change effect the YBSA populations? Might they be more resilient as they feed on such a broad diet of woody perenials?

As always, I am reminded that there is so much more to know. And really, I just want to see a YBSA drilling these holes, but I’ll have to wake up early for that. Early bird gets the sap afterall.

To learn more :
The Birders Handbook by Ehrlich, Dobkin and Wheye (Simon and Shuster, 1988)
Birds of Forest, Yard and Thicket by John Eastman (Stackpole Books, 1997)
Methods and annual sequence of foraging by the sapsucker by James Tate Jr.


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