Just a thought , Back when I was about 10 , {early seventies} I remember when every cattle herd in the area used to have an equally large flock of birds always around them they would sit on the cows backs , sometimes from their shoulders all the way to their tail their backs would be black with birds then sometime in the eightys or so you didn't see this much anymore. To my recollection my grandfather dipped cows in the 60s--70s but we still had birds on their backs I don't mean the birds disappeared altogether, they just quit landing on cows. Later for a lot of years I never saw a bird on a cows back like that, for about 3 decades actually. Now I am seeing a few birds again sitting on cows during the summer, not as thick as before but there are some again. I wonder if it means the bugs are getting immune to warbex or if there is some other reason the birds are starting to come back to the cowherds