I assume that Kilvas did all that because in nature, they are ravens. I know you're probably thinking "Well Duh!" when I say this, but think about this; whenever you see a crow/raven on the street what do they do? They scavenge for whatever trash they can find to keep themselves alive.
This is kinda like Naesala in FE9. He scavenges everything he can do to make a quick buck. I doubt those things had to do with the blood pact. As for the massacre, I don't think he got word of it before it ended. When you talk to Naesala with Reyson in chapter 18 he gets a change of heart.
Anyway, that's how I interpret it. On a side note, after playing both FE9-10 I've started to pay more attention to ravens/crows and like them more, anyone else feel this way?
Man, what's with all the spoiler bars in the Radiant FEs?