An evaluation of video playback using Xiphophorus helleri

Video playback is being increasingly used as a technique for behavioural re search. The importance of critically evaluating the effectiveness of video playback is clear, as available video technology is not designed for nonhum an visual systems. We discuss several aspects concerning the perception of video images that could lead to inconclusive or erroneous results. Research ers should verify that behaviour observed in response to video playback is comparable to behaviour observed in response to live animals. We conducted such a verification using live and video playback methods to measure female response to swords of varying lengths in the green swordtail, Xiphophorus helleri. Using both methods, female response appeared to be an increasing f unction of male sword length. Females did not differ in their response to l ive and video versions of noncourting, noninteractive males, however, femal es tended to prefer video playbacks of males with longer swords, a result t hat has also been found in experiments using live males. These results sugg est that females express the same qualitative mating preference, but not ne cessarily the same quantitative preference, for sword length when viewing v ideo stimuli. Several methodological factors that may contribute to an appa rent difference in the strength of the preference are discussed. Despite th ese differences, both methods produced comparable results; female response to sworded males tended to increase as sword length increased. These experi ments demonstrate that video playback is an effective method to measure fem ale preferences accurately in X. helleri and provide an example of how vide o playback can be evaluated in other species. (C) 2000 The Association for the Study of Animal Behaviour.