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Bird Migration: Influence of Physiological State upon Celestial Orientation
Science (New York, N.Y.)
|August 15, 1969
Summary
Indigo buntings exhibit seasonal migration direction changes due to internal physiological states, not external cues. Spring birds migrate north, while autumn birds migrate south, demonstrating internal control of migratory orientation.
Area of Science:
- Ornithology
- Animal Behavior
- Physiological Ecology
Background:
- Seasonal migration is a complex phenomenon in birds, involving intricate physiological and environmental interactions.
- Understanding the drivers of migratory direction reversal is crucial for comprehending avian navigation and life cycles.
Purpose of the Study:
- To investigate the role of internal physiological state versus external stimuli in determining migratory orientation in indigo buntings (Passerina cyanea).
- To test whether induced spring and autumn migratory conditions influence directional preferences under a controlled environment.
Main Methods:
- Photoperiod manipulation was used to induce physiological states of migratory readiness (spring and autumn) in indigo buntings.
- Orientational tendencies were simultaneously tested under an artificial, spring planetarium sky.
- Directional preferences of birds in spring condition were compared with those in autumnal condition.
Main Results:
- Birds in a spring physiological state exhibited northward orientation.
- Birds in an autumnal physiological state displayed southward orientation.
- These opposing directional preferences were observed under identical external stimulus conditions (artificial spring sky).
Conclusions:
- The seasonal reversal of migratory direction in indigo buntings is primarily driven by changes in the bird's internal physiological state.
- External environmental cues appear to be secondary to endogenous factors in controlling the direction of migratory orientation in this species.
- This finding highlights the importance of endogenous rhythms and physiological readiness in avian migratory behavior.
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