Individuality in the use of orientation cues by green frogs

The common assumption that test groups are motivationally homogeneous and utilize the same orientation reference cues may not be correct. Green frogs (Rana clamitans) were trained in a circular arena to seek a goalbox located 90° counterclockwise from a lamp. Most frogs learned the task, but an analysis of the training and testing records showed marked individuality in task learning. Some frogs found the goalbox only with the lamp as a cue; others used the goalbox, the goalbox and lamp, or the goalbox and the lamp separately as cues. One individual learned to orient non-randomly to some still-unknown but geographically fixed cue. These observations show that even though frogs can learn a common task, under supposedly identical training conditions they may utilize a diversity of cues. Larger (thus, older) frogs were significantly more consistent in their patterns of movement. Paths of movement that succeeded in reaching the goal tended to be repeated in later tests. Frogs trained to move around a partition to a goal continued that path even when the obstruction was later removed, suggesting the use of a motor memory or kinaesthesia. Standard orientation tests, in which the group was significantly oriented in the expected direction, were shown on closer inspection to consist of frogs moving according to several individually stereotyped factors. Thus, the heterogeneity of individual experimental animals should be more fully taken into consideration in orientation research.