can anyone explain this odd bluejay behavior?

[Atman]

5. Territorial defense trickery?

There is a dead branch that extends directly toward our bedroom window. It's three floors up at the back of the house. There is also a nest about 4 feet higher in the tree, which I assumed was the bird's nest.

Each morning a bluejay (or two, sometimes) would land on the branch and shriek like crazy, very loud. Then jump off the branch, but always swooping down in the same direction, never saw them go to the nest. One day, before the leaves were full on the trees, I was able spot where they were going...thier nest was about 20 feet away, about one floor below us.

One Bluejay would stand on the branch by the nest and shriek while down below another was apparently tending to their real nest. The Jay outside our window appeared to be standing guard outside what we found out was a squirrel nest. When one bird would leave the Bluejay nest, the "guard" bird would fly down and take it's place, then come back and shriek at the squirrel nest as the other returned to tend to their babies (or eggs). The whole exercise seemed to be to warn the squirrel to keep away.