Naughty Cayuga duck!!

Well, I adopted a pair of Cayuga ducks about a month ago.  They were found under a bus in the city as tiny peeps.  A year later the good samaritan had to move and I stepped in.  I have a dozen hens and two baby female goats in the same spacey inclosure.  The ducks fit right in and loved their little swimming pool.  We named them Diego and Frida after the artists.  We noticed Diego was very busy with frida, at least 5 times a day, holding her head under the water etc...not so nice, but I guessed this was duck behavior........until he started chasing around our little RHR hen.  She is the top of the pecking order, so I figured being the only male in the whole barnyard, he was showing who was boss.  NO, his intentions were not that honorable!  I had to keep beating him off the poor little hen, who's head was bruised and battered!  Soon he was chasing the bottom of the pecking order a tiny silver Polish named Cher.  Now, that was enough, he was raping my chickens!  I had to seperate the ducks from the hens which really ticked him off.  At this point he was even trying to bully my 11 year old daughter.  Long story short, they are now living with another family who has a single female Cayuga duck (poor thing) along with a yard full of chickens, roosters and pecocks.  He found the single duck in about five seconds and had his way with her.........is this normal duck behavior, because I am thinking I don't like ducks so much anymore!