the past three summers I have had issues with Black Bellied Tree ducks visiting morning and night, right after I filled the feeders...it was like they had a look out in the trees waiting and passing the information on to their flock...it started with a pair and by the end of the summer last year, one evening, I counted 36 of the free loaders chasing my ducks and geese from their feed and pools to hog it all up...it was a problem...I started standing guard out there in the evenings and getting up early so my flock could eat and bathe before the invaders showed up...I was a little worried about disease but realized first of all, I could not stop the invasion completely and secondly, ducks are pretty healthy and don't pass much illness between groups like chickens do...McMurrey sells these ducks, the Black Bellied Tree ducks, for 150 bucks a pair...I don't know who let these guys loose in this area but they are not native to N Fl...more like the Texas coast from what I have read...