In search of water: orientation behaviour of dehydrated natterjack toads, Bufo calamita

Abstract

We analysed the water-finding ability of 12 natterjack toads, after mild dehydration, in an experimental environment (octagonal arena) which provided geo- and hydrotactic, magnetic, olfactory and visual cues for orientation. We tested the hypotheses that the water-finding ability is based on pilotage, using gradients of waterborne cues, and that the cues used for water orientation differ between individuals. Random search behaviour of naıve toads released in the arena showed that goal-oriented movements towards the exit leading to water required previous experience of the position of the water source. Thus, the water-finding ability of natterjacks is restricted to familiar areas. Physiological and behavioural responses to training and testing varied considerably between individuals: six toads became oedomatous and learned how to locate water, whereas the remaining six did not. We analysed the orientation behaviour of successfully trained toads in the training arena, when directional cues were removed or provided conflicting information, and present evidence for individuality in the use of orientation cues: three toads relied mainly on geotactic cues and olfactory pilotage, another mainly on visual landmarks and geomagnetic information, and another used all cues available without clear preference. In conclusion, to detect water, dehydrated toads rely on a multisensory orientation system, which is basically the same as that used during breeding migrations and includes several redundancies.