| Popis: |
The relative importance of vision, audition and olfaction to weasels and polecats was determined by training the predators to find a mouse located in a predator-proof container within a small arena. The diversity of sensory information available to the predators had an effect on the time taken to find the mouse with this being shorter when three senses could be used compared to when one sensory modality was available. Vision and olfaction (air-borne scent) were equivalent, with audition being less important. The mouse was found quicker using substrate-scent cues than with air-borne olfactory cues. There was no difference in the relative importance of the senses between the predators. The removal of movement cues had a significant effect on the behaviour of the weasels. The visual movement discrimination ability of both species was investigated using a horizontally-moving spot on a cathode-ray oscilloscope screen. Thresholds were determined for the discrimination of the direction of a fast-moving stimulus and were equivalent in the polecat and weasel. The mean threshold for polecats was 292cms(^-1) and for weasels was 267cms(^-1). The movement detection ability of the weasel was consistent over a range of stimulus radiant intensities (35.4-2.0x10(^5) µWsteradian(^-l)) and discrimination distances (10-50cm), although there was a slight decrease in threshold at the furthest distance used and when the distance traversed by the stimulus was short. A relative velocity discrimination task was devised in which polecats were trained to discriminate differences in speed between identical objects moving in opposite directions in the horizontal plane. They could detect velocity differences of 20% and showed a tendency to select the slower-moving of the two stimuli. Polecats and weasels do not specialize in the use of a particular distance sense to locate potential prey. In terms of their movement detection ability and the relative importance of vision they are intermediate between strictly nocturnal and diurnal species, which is probably attributable to their predominately crepuscular activity pattern. |
