Ontogenetic development of magnetic compass orientation in domestic chickens ( Gallus gallus )

Domestic chickens ( Gallus gallus ) can be trained to search for a social stimulus in a specific magnetic direction, and cryptochrome 1a, found in the retina, has been proposed as a receptor molecule mediating magnetic directions. The present study combines immuno-histochemical and behavioural data to analyse the ontogenetic development of this ability. Newly hatched chicks already have a small amount of cryptochrome 1a in their violet cones; on day 5, the amount of cryptochrome 1a reached the same level as in adult chickens, suggesting that the physical basis for magnetoreception is present. In behavioural tests, however, young chicks 5 to 7 days old failed to show a preference of the training direction; on days 8, 9 and 12, they could be successfully trained to search along a specific magnetic axis. Trained and tested again 1 week later, the chicks that had not shown a directional preference on days 5 to 7 continued to search randomly, while the chicks tested from day 8 onward preferred the correct magnetic axis when tested 1 week later. The observation that the magnetic compass is not functional before day 8 suggests that certain maturation processes in the magnetosensitive system in the brain are not yet complete before that day. The reasons why chicks that have been trained before that day fail to learn the task later remain unclear.