An Investigation of the ‘Chronometer’ Factor in Bird Navigation

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Abstract
An investigation was made of that part of the sun navigation hypothesis which proposes that birds detect longitude displacement by comparing home time (provided by an internal ‘chronometer’) with local time (estimated from the highest point of the sun arc). Shearwaters were exposed for 4 days, and pigeons for ten days, to an artificial day 3 hr. in advance of normal. This did not result in any confusion of their orientation when released to the east. More drastic treatment was then used, pigeons being subjected to 4–5 days of irregular light/dark sequences, followed by 5–11 days of regular sequences, advanced or retarded with respect to normal. In tests from the west (2), east and north after this treatment, the ‘chronometers ‘had apparently been affected and the birds showed a definite tendency to fly in the predicted false direction—east after an advanced day, west after a retarded one. Variations in the time-in-sight, and in the proportion of the more rapid returns supported the conclusions drawn from the orientation data. In a minority (25 %) of the birds, the evidence suggests that the ‘chronometers ‘were not affected. It is concluded that these new results, taken with those produced previously, strongly support the suggestion that a form of complete, bico-ordinate sun navigation is used by birds.