The Ontogenetic Development of Orientation Capabilities

Emlen, S.T. 1972. In: Animal orientation and navigation. S.R. Galler et al., eds. NASA. pp. 191-210.

The collection of papers presented at this symposium attests to the interest that problems of animals orientation have aroused in both physiologists and ethologists. One phase of orientation research, however, has received little mention. This is the question of the ontogenetic development of orientation capabilities.

Early field observers reported that among many species of birds (primarily shorebirds) the young migrate southward independently of adult conspecifics, hence orienting correctly without any prior migratory experience. As a result of such findings, migratory orientation became a classic example of an "innate" behavior (refs. 1-4). Unfortunately, this rather arbitrary labeling discouraged further research on the actual maturation of navigation behavior.

Actually, field experiments conducted over a decade ago suggested a dichotomy of navigation capabilities between young and adult birds. When birds of several species were captured and displaced from their normal winter quarters while immatures (birds on their first migration trip) did not, but rather took up courses parallel to the original direction of migration (refs. 5 to 8). This implies an improvement in navigation performance as a result of previous migratory experiences.

I arrived at a somewhat similar conclusion from studies of the migratory orientation of caged indigo buntings. Several years ago I naively was trying to locate the critical star pattern for celestial orientation in this species. My approach was to remove portions of a planetarium sky and look for disorientation among the birds. The results (ref. 9) demonstrated a high degree of redundancy in the celestial orientation system; different individual birds employed different "strategies." Thus one bunting required the entire area within 35 degrees of Polaris for successful orientation while another individual required only a small portion of that circumpolar area. For one additional bird, the northern stars were not essential at all. Such results suggested a level of individual variation hard to reconcile with the idea of a predetermined star map under rigid genetic control.

These considerations have led me to study the orientational capabilities of hand-risen indigo buntings. This paper represents a summary of all such experiments performed to date. Portions have been adopted from studies already published (ref. 10) or currently in press. I am grateful to National Institutes of Health (through a health science advancement award to Cornell University) and the National Science Foundation (through GB 13046 X) for financial assistance. I also thank Margaret Platt and Carol Conley for help with experimental series II and II, and members of Cornell's Orientation Seminar Group for comments and criticisms.