Birches' and maples' sap runs in the spring. Open wounds leak the sap. Your woodpecker is probably the cause. But I wouldn't worry that your trees are fatally damaged. Soon the sap will stop running.

Interesting! We noticed that too today. The River Birch overhangs a sidewalk and I guess its easy pickings for passersby who like to pull at the low hanging branches. It almost looked like it had rained recently or smthg...because the sap was hanging from several branches.

If a woodpecker is bothering your tree, it's probably trying to get bugs inside the trunk. Not a good thing.

Just a warning: we lost two trunks of a beautiful triple-trunked river birch clump to yellow-bellied sapsuckers at our old house (diagnosed by the folks at our local ag station when I took in a chunk from the point at which the trunk broke off -- they immediately identified the traces of a circular "ring" of bore holes around the trunk at the point at which it broke off). You might look carefully for actual bore holes, and try to ascertain what's going on. We were told that once the sapsuckers "found" our trees, they would continue coming back to our particular trees each year, so you'd want to take preventive measures, whatever those might be. We bought ours ("Heritage") because we thought it was less prone to borers than other birches. But I assume those sapsuckers were after something...?

Here is a link that might be useful: {{gwi:337899}}