Duckie genetics question

[Knighstar679]

I am looking at the genetic calulator online. I put in some birds I might get and ended up with a curious question from the experiment.

Male
mdmd Li+Li+ EE bl+Bl C+C+ B+B+ r+r+ dd Bu+Bu+

vs
Female
mdmd Li+Li+ EE bl+Bl C+C+ B+B+ r+r+ d- Bu+-

Is there are reason why none of the predicted females have the last Bu+ but all of them are -. What does this mean exactly though. From my understanding it is a link to the buff gene is that correct?

 

[Ratchnick]

I'm just guessing but i think it means that the loci for that gene is only on the W (long) chromosome.