At 4 months of age, they're still quite young, and may or may not have reached maturity. 

 Most likely, this isn't the extent of their interest in pullets (wouldn't it be nice if I'm wrong, though? 

). I'd monitor them closely in another month or two, just to ensure the girls aren't in distress. Some chasing is normal (and will hopefully subside after time), but I, personally, don't put up with feather loss, drawn blood, or pursuit of pullets to the point of misery. Best of luck with your boys! 
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I won't put up with any wounding, either... I'll keep a close eye. It would be soooo nice if they didn't have any more interest than what they are showing now!
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You've liked d'Uccle cockerels thus far? 

 Sadly, I didn't, but this was my own doing. 

 We live and learn. I'll probably give them another, fair chance in the near future. 
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 Yes, the d'Uccle boys are nice...but no, not my favorite of the boys. It's just the one d'Uccle is really beautiful and so far a very good leader/rooster. He is very gentle with everyone--not very tame--but I hope with time that improves. The Sebright boys were the worst!! I think it would be smart to only have Sebrights, not keep them with other breeds. They were lovely on their own, but not nice to the others. I love all my other boys and yes, just as much as the girls. Why can't we just neuter them like dogs?!! Grrr...annoying. I wish there was a humane capon surgery because I would get it for all of them and keep them as pets.
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Goodness, it sounds as though every breed has their individual personality! And how nice you've encouraged them all to enjoy human interaction. 

 It's a breath of fresh air to associate with people who love their cockerels every bit as much as pullets. 

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Thanks for all the great advice!