Wow, okay, so the bad rap wyverns have is evidently totally justified.
Wyverns, while loyal to their own family groups or comrades, are extremely vicious and cruel to outsiders, especially when in battle, one of the many reasons they make such devastatingly effective soldiers.
Not all wyvern species are like this. The wyverns we’ve seen so far in Eryl are all northern river wyverns, which are among the most intelligent and aggressive species. There are others that are more vicious, but smaller and less intelligent, and others as smart but much less interested in consorting with humans. Most species live in very specific habitats and are small in number. The northern river wyverns are by far the most populous, due to being able to adapt to a large number of climates.