1Ecology, Evolution, and Environmental Biology, Columbia University, 2NYCEP, New York Consortium in Evolutionary Primatology
Friday All day, Plaza Level
Assessment of variation in physical traits such as skeletal length, intermembral index, and numerous cranial and postcranial dimensions, is fundamental to many studies relating to systematics, locomotion, energetics, development, competition, and sexual selection (to name only a few). As many researchers have noted, however, accurately measuring size of physical traits of animals in the wild can be extremely challenging. Restraining wild animals can be difficult, dangerous, and expensive, and is likely to adversely affect other aspects of a study. We examined recently described non-invasive methods of measuring free-ranging animals and found a convergence on photogrammetry – using photographs of subjects to estimate body size based on mathematically inferred scales. In several studies, the mathematical principle, equipment, and methods employed were extremely similar. However, in published results as well as our own replication of methods, we found that error frequently exceeded 3% and thus risked obscuring inter-individual differences. We developed and tested a refined method of photogrammetry that is simple to use, affordable, and is appropriate for field studies of primates. In comparisons of actual size to estimated size, there was a mean error of 0.7% with a range of 0-1.9%.