Recent Experiments on Bird Orientation

Summary. Pigeons raised in open aviaries show homeward orientation when released 100 or 150 km. away from their home aviary. Some of them (15–20%) actually return. When palisades are placed around the aviaries orientation vanishes. The palisades allow the birds free sight of the sky except for a zone of an elevation of 3° above horizon. Orientation is absent also in pigeons raised in an aviary giving view of a broad sector to the north, i.e. the direction opposite to release. These experiments are being continued. Homing pigeons were subjected to an artificial light/dark change (period 24 hours). If the artificial cycle was out of phase with the natural day/night cycle, the “internal clock” was shifted within three to four days as shown by directional responses. Basically the same deviations are shown by “shifted” pigeons taken away from home and released. What appears to be influenced by shifting is a directional response which must necessarily rest upon a previous determination of position relative to home. This preceding part of the whole orientation performance appears to be unaffected. Orientation is influenced by spatial factors, or factors related to space, of unknown nature. The observed phenomena may be tentatively subdivided into variations due to direction, site of release place, site of loft, and region. Among weather conditions, cloud cover has a significant influence upon homing orientation. Top‐class homing flights are less frequent with overcast. Homing ability is subject to an annual fluctuation. Homing is best in August and poorest in January. Parallelity to temperature is obvious throughout the year. Correlation between particular releases and temperatures prevailing at the particular occasions exists only in autumn and winter but not during the rest of the year. A correlation has also been found with interdiurnal barometric change. This correlation is scarcely perceptible at surface level, but significant at the 500 and 200‐mb. level. This correlation concerns homing performance as well as correctness of departure directions, but not scatter of departures. So far no cross relations can be established between results attained with the different ways of approach. It is thought that homing ability as shown by the domestic pigeon continues to be a problem of ornithological interest. It is assumed the same ability is possessed by wild species.