The Development of Orientation and Navigation Behavior in Birds

Abstract

The complex mechanisms of orientation and navigation in birds develop through the interaction of experience with the relevant stimuli and the underlying genetic substrate. Many migratory species show site fidelity, homing to previously occupied breeding and overwintering localities. The ability to do this requires experience at the site and involves a process like imprinting that seems to take place at least twice during a bird's first year of life. On the first migration, birds fly directions and distances that are apparently genetically programmed and are sufficient to bring them within the winter range of their population. Little else is known concerning the genetic basis of orientation behavior. The sun, stars, and earth's magnetic field provide compasses for migratory and homing orientation. The ontogeny of each sort of compass involves experience-dependent modification during at least the first few months of a bird's life. The sun compass is learned by observation of the sun's arc in concert with the bird's biological clock. There is some evidence that the magnetic field may also be involved in calibrating the sun compass of the homing pigeon. The star compass is established through visual observation of the axis of stellar rotation during the bird's first summer. The pole point is defined as north, but the biological basis of this rule is unknown. The sensory basis of the magnetic compass is also unknown, but it is subject to modification by visual cues, probably stars. In this article we discuss the varying degrees of plasticity in the ontogeny of these mechanisms within the evolutionary context of the spatial and temporal variability of the relevant orientation cues. There appears to be a trend in which information flows from more reliable to les reliable cue-systems during development. In addition to a compass, goal-directed orientation, or navigation, requires some means of assesing location relative to the goal. Homing pigeons apparently utilize sensory information acquired during the displacement journey in this context, but such input does not seem to be necessary. The ability to navigate using only those cues available at the release point is thought to be based on a map of some sort. The bases of this map remain controversial: current investigations are focused on odors and magnetic gradients, but these are not mutually exclusive possibilities, nor are they the only ones. In both of the above cases, there is evidence of experiential effects, and we believe that an ontogenetic approach may elucidate the essentials of these mechanisms. Studies of the ontogeny of bird navigation are also likely reveal important things about the development of behavior in general.