INTRODUCTION

A bird uses a variety of cues to navigate accurately. One cue is the direction of the sun. However, because the sun is continually changing its position in the sky, a bird also needs other information—such as the time of day—to determine what the sun's position means.

In the accompanying animation, we describe an experiment that tests whether pigeons use what is called a time-compensated solar compass to determine compass directions. That is, does a pigeon use an internal clock, called a circadian rhythm, to assess the time of day and thereby interpret the sun's position in the sky?

CONCLUSION

It appears that pigeons and perhaps other birds use their internal clocks (circadian rhythms) to determine compass directions from the position of the sun. In the Northern Hemisphere, if their internal clocks say it is noon, the sun should be located in the south. Likewise, if their clocks say it is late afternoon, the sun should be located in the west.

Clock phase-shifting experiments provided the evidence for this conclusion. Pigeons were put in a room where the light/dark schedule could be shifted with respect to real time. Exposure for 2 weeks to a light/dark cycle in which lights came on at midnight caused a 6-hour phase advance of their internal clocks. Thus, when they were returned to the outdoor cages, the birds saw the sun rise when their internal clocks indicated it was noon. As a result, these birds, trained to seek food in the south, oriented to the food bins in the east. A 90-degree error in their orientation was induced by a 6-hour phase shift of their internal clocks.

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Textbook Reference: Concept 40.4 Moving through Space Presents Distinctive Challenges