I don't know if it's "wasteful" for birds to barf. I saw
Black-crowned Night Heron a few years ago, come to shore, then vomit,
and then proceeded to eat it over again. I think it stuffed itself at
shore to avoid competition, then went somewhere else to enjoy it properly:
http://blackfoot.net/~larkwick/Herons_Egrets_Goleta.html
- Jim in Montana