Sounds like you got them from a hunter friend, scrape any meat/fat off if you can. Then use salt to help dry them out. Then borax after that, be sure to keep them away from your other materials until you are sure they are dried and bug free.
There's no meat and/or fat on the feathers. I did get them from a "hunter friend". So just pour some borax in the bag of feathers and let them dry, or lay the capes out in the garage on a flat surface and let them dry with the borax on them?
Borax is a much better choice for drying and curing bird skins. Salt is hydrophilic, attracting and absorbing moisture and in humid weather will cause the skin to become damp and sticky. Be sure to use straight borax and not Boraxo which is a mixture of borax and soap.
+ 1 for Borax. bag them per each in a ziplock bag. 1 cape/neck/tail group per bag. i put mine in the garage where its cool temp wise. i used ample borax, then just shake the bag to get the feathers coated good. and leave em for at least a month.