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Seasons of Life – Russell G Foster and Leon Kreitzman

If the sun is to be used as a navigation aid, there must be a way of compensating for its apparent movement across the sky.  If a bird in the northern hemisphere wishes to fly south, it needs to keep the easterly sun on its right in the morning at 6.00am, fly towards the southerly sun at noon and keep the westerly sun to its left in the evening.

In the 1950s, Gustav Kramer was the first to show that the sun was used by different bird species to navigate and that they could compensate for the sun’s apparent movement across the sky. 

Kramer’s initial experiments were on European starlings, which he trained outdoors to fly off in a particular compass direction to get a food reward.  He suspected that the birds were using the sun’s position in the sky as a compass.  To test his hypothesis he moved the starlings indoors, replacing the sun with an electric light as a direction giver.  As before, the birds inside would similarly move off in a particular compass direction for the food reward, but this time using the light bulb as an orientation cue.  The electric light was fixed in position; remarkably, although the birds would move off in the direction of the food, they added 15 degrees of arc (anticlockwise) each hour to the angle they made to the artificial sun.

Kramer concluded that the birds must ‘know’ that the angular velocity of the sun’s azimuth is approximately 15 degrees per hour, that they have some clock to compensate for the moving compass and that they ‘knew’ that they were in the northern hemisphere (Kramer 1952)