Gilbert Gottlieb was an elegant experimentalist whose research was inspired in part by naturalistic observations of parent-offspring vocal-auditory interactions of waterfowl. Such observations are essential in identifying potential linear (obvious) as well as nonlinear (subtle) mechanisms underlying the development of species-typical behavior. His series of experiments on the development of species identification in birds illustrates the fruitfulness of his conceptual and theoretical approach, which also inspired my own work on alarm call responsivity of ducklings. The respective developmental systems we studied both in nature and in the lab are greatly influenced by nonlinear experiential factors and also illustrate multiple pathways toward developmental outcomes.