Vomit is, for the birds, of fearful value, suggests this study:
“Rollers smell the fear of nestlings,” D. Parejo, L. Amo, J. Rodríguez and J.M. Avilés, Biology Letters, epub 2012. The authors, at EEZA, CSIC, Almería, Spain, report:
“Some bird species produce chemical compounds when threatened, such as nestlings of the Eurasian roller Coracias garrulus [pictured here, via Wikipedia] that vomit an odorous orange liquid when scared in their nests. Here, we experimentally explore the possibility that parents were informed about recent predation attempts at their nests through the olfaction of this vomit.”
(Thanks to investigator Nick Carstoiu for bringing this to our attention.)