I suppose... they don't really seem to have been studied very well. I tried finding books on them, but most of them are just picture books for kids.

[Kids and pokemon.]

It might be that this behaviour is... normal for them in some way. There are other pokemon that are very territorial. Maybe what we are seeing is just them fighting over territory. Granted, it's on a much larger scale than two pidgeys squabbling over a branch, but it might still be the same thing.