Anosmic pigeons orient from familiar sites by relying on the map-and-compass mechanism

Abstract

Abstract. Since homing pigeons, Columba livia, are able to orient homeward when released from familiar sites deprived of their sense of smell, they are thought to rely on other information acquired during previous experience with the release site. They may either follow a chain of landmarks to reach home without resorting to their sun compass (piloting mechanism) or fix their position from known landmarks at the release site and then select the home direction by the sun compass (map-and-compass mechanism). Which mechanism is used was investigated by testing the influence of a clock-shift treatment on the orientation of pigeons released from familiar sites. In four experiments, clock-shifted pigeons, some anosmic and some not, displayed an anticlockwise deflection in their initial orientation, as was expected on the basis of the fast clock-shift treatment applied. In all cases their bearing distributions differed significantly from those of non-shifted ones and the homing performances were significantly worse. Most of the clock-shifted birds made anosmic by a long-lasting treatment were lost. These results show that pigeons released from familiar sites rely on olfactory cues and known landmarks to determine the home direction, which is then selected using the sun compass. When rendered anosmic, they do not switch to a piloting mechanism but still use a map-and-compass mechanism, resorting to a mental map of familiar sites developed during previous training flights.