thomasisclever

It could be blood feathers fallen off, because new feathers usually have blood vessels in the core. Is he/she pruritic? If the lesion is itching, it could be things like parasites, allergy. Moulting can be one of the cause too. For beak and feather disease (PBFD), the feather should be dystrophic, and the lesion should be predominantly in the primary and tail feathers

thomasisclever

There are two form of PBFD, acute vs chronic, it is like human AIDs, most of the damage is done thru immunosuppression.
Acute = seen in juveniles, around weaning age. These bird are usu lethargic, fluffed and anorexic. Hamematology may show pancytopaneia (decreased RBC, WBC, platelets) and non regenerative anaemia.
Chronic = progressive replacement of normal feathers with dystrophic feathers
In this case, it could still be acute PBFD, but not chronic form
Hope ur baby bird get well soon!