Board Thread:Episode Discussion/@comment-14138255-20180123171649/@comment-24994749-20180124195448

73.Anon.52 wrote: if anything, it's likely an indicator of whatever magic allows the branwen twins their bird forms... and even then it still doesn't mean Yang will ever be able to do so. It was explicitly stated that the ability to turn into birds was given to them by Ozpin...

Unless you meant their eyes turned red after Ozpin gave them that power.