We have a pin oak tree approximately 20-40 Feet tall. It is now losing clumps...
This sounds like squirrels. They pretty typically do this, not just earlier in the season when nest building, but later too.
I really doubt it's caused by squirrels as there are so many droppings every day. We are constantly picking up these branches. Are there fungus or insect issues that could be causing the problem. We have never had this problem before with so many clumps falling. Of note, at the end of the branch clumps it looks like it just broke off and chewed off.
We have a plant pathologist and entomologist on staff and have no pathogen or insect issues. Earlier in the growing season twig girdlers(sharp end cut) and twig pruner(concave cut) can do this, but not at this time of year. In any case, there is nothing to be done for it.
This is a perennial question for us in late fall, and it is quite probably squirrels.