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He can and, if you let him or he wants, will fertilize their eggs. The ducklings will be a mix of pekin and which ever female he mated with and you might get some interesting colors and patterns from this. Post pics of ducklings if you get any I'd like to see what these mixes would throw.
Yes he would likely be able to reproduce with them. My experience with pekin males is they are rather brutish with the females so I would recommend more females to distract him.
The offspring would be a mix or mutt if you will. They would be mostly black and have white spotting from my experience with pekin and cayuga. I had a male pekin and female cayuga and that is what they created. I had other females of different breeds as well and had to separate when he was to aggressive with the gals.
Personally I was not as fond of the male pekin as I would have liked to be. He would "favor" the cayuga female to the point she was terrified of him.
Getting more and making separate pens is a good idea. I would also recommend a "time out" pen for any male that was to aggressive with the ladies.
Mine would have been in there all the time for sure.
If you are going to let anyone hatch ducklings out make sure they are well protected with really good fencing. I had a fox issue where I lived. The eggs would get to within a week of hatching and the fox would dig into the pen then snatch each and every egg from the nest.
Skirt that pen with a good strong apron and keep a lid on it to save the little ones from attack.
I tell you that since I knew little of owning ducks when I started and made mistakes in my enclosure that cost a couple nests and a few ducks. I know more now and wish I had known then.
I am sure you will have better luck with yours as you have found the BYC community. So many helpful folks on here and such nice people.