The Discrimination of Natural Movement by Budgerigars (Melopsittacus undulates) and Pigeons (Columba livia) Rosetta Mui, Mark Haselgrove, Anthony McGregor, and James Futter Cardiff University Cecilia Heyes University College London John M. Pearce Cardiff University Three experiments examined the ability of birds to discriminate between the actions of walking forwards and backwards as demonstrated by video clips of a human walking a dog. Experiment 1 revealed that budgerigars (Melopsittacus undulates) could discriminate between these actions when the demonstrators moved consistently from left to right. Test trials then revealed that the discrimination transferred, without additional training, to clips of the demonstrators moving from right to left. Experiment 2 replicated the findings from Experiment 1 except that the demonstrators walked as if on a treadmill in the center of the display screen. The results from the first 2 experiments were replicated with pigeons in Experiment 3. The results cannot be explained if it is assumed that animals rely on static cues, such as those derived from individual postures, in order to discriminate between the actions of another animal. Instead, this type of discrimination appears to be controlled by dynamic cues derived from changes in the posture of the demonstrators. Keywords: movement discrimination, budgerigars, pigeons, dynamic cues The behavior of one animal is often affected by the behavior of another animal, as the following examples illustrate. Burmese jungle fowl are more likely to peck at a distinctive dish if they have observed conspecifics engage in the same activity (McQuoid & Galef, 1992, 1993); budgerigars that observe another budgerigar remove a stopper from a box to obtain food tend to copy this action (Mottley & Heyes, 2003); and the courtship behavior of a bird such as the western grebe can be intricately related to the behavior of its partner (Nuechterlein & Storer, 1982). The obvious implication of these diverse examples is that ani- mals are able to tell the difference between the various actions and movements of other animals and to react accordingly. Given this conclusion, the question then arises as to how such discriminations are made. When any animal engages in a natural movement it can be regarded as executing a sequence of postures. It is possible that an animal discriminates between the actions of another animal on the basis of the information provided by a single posture from this sequence. For example, the sight of a bird bent over with its beak touching a container might have been sufficient to make the observers in the study by McQuoid and Galef (1993) perform the same response. In the study by Mottley and Heyes (2003), the observers may have simply copied the relevant postures of the demonstrators, rather than entire movements. And a stance offered during a courtship display may be sufficient to encourage the partner to react in a certain manner. A particular posture can be described as a static cue, because it does not depend upon the movement of the demonstrator for it to occur. All that is necessary is for the observer to detect a single posture within an activity and to use this posture to identify the activity. Of course, sufficient information for the discrimination to be successful could be derived from either the single posture as a whole, or from a relevant fraction of it. It is not of present concern to choose between these alternatives, and we thus regard static cues as emanating from individual postures of the demonstrator without considering their nature in more detail. Rather than refer to static cues, the actions of a demonstrator might be identified by the movement that is created. Any activity will generate what we refer to as dynamic cues, which depend upon changes in posture for their existence. Thus it might have been the sight of a demonstrator’s beak moving toward and away from the bowl that had an effect on the behavior of the observers in the studies by McQuoid and Galef (1992, 1993), or the sight of the demonstrator actually moving the stopper in the study by Mottley and Heyes (2003) that encouraged the observers to engage in this activity, or the sight of an elaborate sequence of postures in a courtship display that resulted in a response by the partner (Nuechterlein & Storer, 1982). A major concern of the present article is to determine whether animals make use of such dynamic cues when discriminating between the actions of other animals. Rosetta Mui, Mark Haselgrove, Anthony McGregor, James Futter, and John M. Pearce, School of Psychology, Cardiff University, Cardiff, Wales, United Kingdom; Cecilia Heyes, Department of Psychology, University College London, London, England. This research was supported by a grant from the United Kingdom Biotechnology and Biological Sciences Research Council. We thank Tim Haselgrove for his help with preparing the video clips and Dennis Price for constructing the apparatus. Correspondence concerning this article should be addressed to John M. Pearce, School of Psychology, Cardiff University, Tower Building, Park Place, PO Box 901, Cardiff, Wales, United Kingdom CF10 3YG. E-mail: pearcejm@cardiff.ac.uk Journal of Experimental Psychology: Copyright 2007 by the American Psychological Association Animal Behavior Processes 2007, Vol. 33, No. 4, 371–380 0097-7403/07/$12.00 DOI: 10.1037/0097-7403.33.4.371 371