Feel like singing

I've been watching this western kingbird along with its mate for several weeks now. They had two chicks in their nest that hatched a week or so ago. I would visit them most every morning as the nest was located perhaps eight or nine feet off the ground. I was saddened to arrive Thursday morning to find the nest had been knocked down and broken apart. The parents were still there protecting the tree but no sign of the chicks. We've had a lot of windy days this summer but this was a very solid nest and would have fallen on soft ground. The dried mud bowl of the nest was all broken apart. My gut feeling is this was caused by a human, this area has a history of people doing things to drive away birds and animals. Would a natural predator do this kind of damage to the nest? I can see them taking the chicks but would they knock a solid nest out of a tree and break it apart? Again I have no proof it was human caused but was just wondering what some of you think? I'll post a pic of the chicks tomorrow less then 24 hours before they disappeared.

D300s
Nikkor 300mm f4, 1.4 TC (420mm)
ISO 400
1/1000 @ f/5.6
HH
PP-NIK & PSCC

Thanks for looking.