Sapsucker nests and Fomes fungi

A beautiful northern Michigan forest, filled with aspen, cherry, and other trees, and underlain with a dense growth of bracken fern. The forests here are typically mixed, with conifers: white spruce, balsam fir, white cedar, jack, red, and white pines, and depending upon the moisture regime, black spruce and tamarack.

It's a yellow-bellied sapsucker, Sphyrapicus varius, paradise, and this is probably the most common breeding woodpecker in Presque Isle County. Northern flickers certainly give the sapsuckers a run for the money in the abundance department, and downy, hairy, pileated, red-bellied, and red-headed woodpeckers can all be easily found as well.

An old paper birch log litters the forest floor. Note the prominent well fields drilled by sapsuckers long ago. There is ample evidence of sapsucker activity in these woodlands, especially in the form of the perfectly arranged rows of cavities created by feeding operations.

Sapsuckers drill and maintain extensive well fields in a variety of trees. Sap flows from the wells, giving the birds a ready source of sugary food. An entire food web is spawned by the sapsucker well fields. A great many insects come to feed at these excavations, and other vertebrates come in to feed on those insects, if not the sap itself.

The wells in this photo are drilled into the phloem tissues of the birch; round sapsucker holes tap the xylem layer. The rewards of such drilling and well field maintenance are great: paper birch, for instance, can have summer sap in the phloem of up to 16% sugar concentrate.

A female yellow-bellied sapsucker warily eyes your narrator. Those of us who live south of the sapsuckers' breeding range usually think of this as a rather shy and retiring species. And they are, usually, at least in winter and migration when compared to the other woodpecker species. But sapsuckers become much more extroverted on the breeding grounds, especially the males. The birds frequently give their highly distinctive drums: a short series of hammer blows that slows in speed, and sounds as if someone is tapping out a telegraph. The birds also frequently give soft mews, and even a loud raptorlike call.

This spring, while leading my annual NettieBay Lodge birding and nature forays, I found several active sapsucker nests. The entrance hole is a very neat affair. Nearly perfectly round in the center, the entrance is carefully sculpted with flanged openings on the top and bottom.

This year, we were fortunate indeed to have David Govatski on one of the trips. Dave is a forester from New Hampshire, and a wealth of natural history information. He taught me something about sapsucker nesting that I did not know. Sapsuckers often select aspen trees for nest sites, such as this quaking aspen, Populus tremuloides. That I knew, and always figured the birds chose aspen because it is a soft wood. Yes, but there's more to the story.

Note the fungus projecting from the tree below and slightly right of the cavity. That's the heartwood decay fungus, Fomes igniarius var. populinus. Sapsuckers are especially fond of aspen that have been colonized by this native fungus.

A stunning male yellow-bellied sapsucker nervously watches us inspect his nest cavity. We did not tarry. Note the animal's bright red throat, a feature that distinguishes it from the female.

This is the best shot I could manage of the interior of the sapsucker nest cavity. We can see the darker softer punky wood within - the effects of the Fomes fungus. Clever birds that they are, the sapsuckers know that it's easier excavating a deep nest hole in an aspen infected with this fungus, and seek out such trees.

Managers of "sugar bushes" - sugar maple groves managed for syrup production - also know about the sapsucker/Fomes fungus connection. They will often remove fungal-infected aspens from the sugar bush, in an attempt to keep the sapsuckers from inhabiting the area and drilling well fields into their sugar maples.

Learn something new every day.