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New stat for detecting change in direction - useful to characterize migration start?

Byrne, R.W., noser, R., Bates, L.A., and Jupp, P.E. 2009. How did they get here from there? Detecting changes of direction in terrestrial ranging. Animal Behaviour. doi:10.1016/j.anbehav.2008.11.014

Efficient exploitation of large-scale space is crucial to many species of animal, but the difficulties of studying how animals decide on travel routes in natural environments have hampered scientific understanding of environmental cognition. Field experiments allow researchers to define travel goals for their subjects, but practical difficulties restrict large-scale studies. In contrast, data on natural travel patterns are abundant and easy to record, but hard to interpret without circularity and subjectivity when making inferences about when and why an animal began heading to a particular location. We present a method of determining objectively the point at which an animal’s travel path becomes directed at a location, for instance a distant feeding site, based on the statistical characteristics of its route. We evaluate this method and illustrate how it can be tailored to particular problems, using data that are (1) synthetic, (2) from chacma baboons, Papio ursinus, where travel is from a single sleeping site in an overlapping home range, and (3) from chimpanzees, Pan troglodytes, where sleeping sites are unlimited within a large territory. We suggest that this ‘change-point test’ might usefully become a routine first step in interpreting the decision making behind animal travel under natural conditions.