Park, T.J., Dooling, R.J., Rock, S., and Okanoya, K. (1989). Discrimination of natural contact calls by two strains of canary and the budgerigar. Journal of Ethology (Japan), 7, 167-169.

Animals and their communication signals make up a unique environmental world. The sender of the signal, the signal itself, and the receiver interact to produce a complex communication system. Evidence is accumulating that many species of animal are especially adapted not only for producing species-specific communication signals, but also for perceiving such signals (Marler 1984; Dooling & Hulse 1989).