Response to a looming predator

Efficient mechanisms which allow an animal to evaluate the threat posed by potential predators are paramount to survival. These mechanisms help to ensure that an approaching predator is not missed. Animals can detect predators using visual, olfactory, auditory and tactile cues. Dynamic visual cues are likely to be important for animals such as Jacky lizards, which rely on visual motion for locating prey as well as for communicating with conspecifics.

With the assistance of staff at Taronga Zoo (Sydney, Australia), Paul Carlile and I obtained sequences of a representative raptor (Barking Owl, Ninox connivens) swooping towards a digital video camera [Top right]. Although the Barking owl is not a known predator of the Jacky Dragon, it shares similar characteristics to known predators (Kookaburra, Dacelo novaeguineae Nankeen kestrel, Falco cenchroides). Presentation of such footage to captive lizards via high resolution monitors evokes anti-predator responses such as fleeing to a refuge. An example of this can be seen in the Quicktime movie [middle right] - the lizard is just below the window showing the stimulus.

As can be seen from the QuickTime movie of the swooping raptor, the dynamic cues that characterise this event include changes in apparent speed, size and shape. To test the relative importance of these cues, we borrowed techniques developed in developmental psychology to study visual processing in infants. We constructed a stimulus featuring a black disc that matched the dynamic properties of the bird (area change/time), but lacked morphological cues such as broad outstretched wings [bottom right].

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Last updated: December 12, 2006