My Female KC likes my pullet RIR...too much.

[AnaD]

I gave away my two drakes and now my KC has two duckling buddies to hang with, but... When I free range my chickens in the evenings my KC finds my RIR and follows her around chortling(?) and bobbing her head to the side. Then she will lay down next to the RIR who looks at her like she is crazy and then pecks her quite hard...Why isthis happening? Will, my duck learn to not do this? How many pecks does it take!? Also, I'm guessing this means she is sexually mature, does this indicate how long it will be before she lays eggs? She is only 13 weeks old.