plucked?

[loot4louie]

2 hens raised together, both laying and approx 1 year. They appear to be friends. 3 days ago Topper lost her topper? It appears plucked? Any suggestions. No blood, no aggressive behavior.

 

[loot4louie]

FYI she is a silky cross and lives solely with her hatch mate who is a slightly larger mutt.

 

[loot4louie]

I will add she is a very broody girl. Could it be nutritional? Hormonal?