Molting at different times

by Maggie
(Northwest Indiana)

Cosmo my catalina loses a couple feathers at a time then new ones grow in...I totally understand that concept, BUT
Bella my B&G loses down feathers all the time-she is never completely bald but tends to get really thin in feathers but theres always pin feathers underneath-so I don't think she is plucking...but she loses her regular feathers like 20 at a time and then before you know there are 20 new pinnies. It seems like she just has thinner amount of down than Cosmo's (her's is white and Bella's is grey and denser), is this genetics?

So my question is is this bird dependant? species dependant? gender dependant?
You would think that since they are in the same room and have the same amount of lighting that they would molt similarly, right?

Should I give Bella any special supplement during the periods of heavy molting?