we don't (yet) have a lot of west nile here. about 5 years ago, these birds started showing up from time to time. over the course of the next couple of years, i watched them harass the redtails. one day, the redtails were gone and these were here to stay. i felt kind of bad, the redtails had been here for many years.
i don't know if it's coincidence, but at the same time i lost the redtails, the swallow population went way up. that's not a good thing for my bees.