Might be coming from inside the tube (it's an alder which is doing quite well as you can see from the tube splitting - only planted 3 years ago). Looks like too much to be cuckoo spit
Luke, first time I've noticed it and it has been raining quite heavily. Perhaps it's a similar mechanism to the DOC foam you get on ponds?
It was gone today so obviously not waterproof - I'd have thought an animal protective foam would be a little more resilient?