User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-2049092-20120215124604/@comment-5020152-20120727160554

"Raptors" were the early ancestors of birds (or at least, very close relatives), so it makes sense that they'd be classified as Bird Wyverns and not Brute Wyverns. They're not that brutish anyways, they're more quick and agile, despite their bulk.