said by Jon:
Cause killing them is always the answer.
It's effective and low cost, so yeah, it's at least AN answer. His tree is being destroyed, now, and so action is warranted.
Trap and release may be another answer, with the risks attendant of near contact with a live, very upset wild mammal. Rabies, fleas and other diseases may be present in these critters, plus it can take more time and be less effective in the short term.
What other "answers" can you think of that will work well, quickly and with little risk to the people that have to put up with them?