title: Validation of two independent photogrammetric techniques for determining body measurements of gorillas.
abstract: The ability to accurately measure morphological characteristics of wild primates in the field is challenging, yet critical for understanding fundamental aspects of their biology and behavior. Recent studies have shown that digital photogrammetry can be used to non-invasively measure morphological traits of wild primates, as it allows for the determination of geometric properties of objects remotely from photographic images. We report here on a rare opportunity to test this methodology by comparing measurements obtained directly from living great apes to those obtained from photographs. We test the accuracy and precision of two independent photogrammetric techniques, employing the use of parallel lasers and a distance meter, respectively, for obtaining measurements of static objects and captive western lowland gorillas (Gorilla gorilla gorilla) (n = 4) at Zoo Atlanta. For static objects, the mean percent error between corresponding measurements collected by the same observer directly versus using photogrammetry was 0.49-0.74% for the parallel laser method and 0.62-0.76% for the distance meter method. For gorillas, mean percent error between corresponding direct and remote measurements was 2.72-5.20% for the parallel laser method and 2.20-7.51% for the distance meter method. Correlations between direct measurements and corresponding parallel laser and distance meter measurements of gorillas were highly significant with R2values and slopes approaching 1.0 (parallel lasers: R2= 0.9989, P < 0.0001; distance-meter: R2= 0.9990, P < 0.0001). Further, variation between measurements of the same targets collected repeatedly by the same observer, and between different observers, was uniformly low across methods (CV, range = 0.003-0.013). While errors are slightly higher for the distance meter technique, both methods show great promise for addressing a wide range of questions requiring the non-invasive collection of morphological data from wild primates. Am. J. Primatol. 78:418-431, 2016. © 2015 Wiley Periodicals, Inc.
authors.affiliation: Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington DC.
authors.forename: Jordi
authors.initials: J
authors.lastname: Galbany
authors.affiliation: Dian Fossey Gorilla Fund International, Atlanta, Georgia.|Zoo Atlanta, Atlanta, Georgia.
authors.forename: Tara S
authors.initials: TS
authors.lastname: Stoinski
authors.affiliation: Dian Fossey Gorilla Fund International, Atlanta, Georgia.
authors.forename: Disier
authors.initials: D
authors.lastname: Abavandimwe
authors.affiliation: Global Conservation Program, Wildlife Conservation Society, Bronx, New York.
authors.forename: Thomas
authors.initials: T
authors.lastname: Breuer
authors.affiliation: Department of Physics, The George Washington University, Washington DC.
authors.forename: William
authors.initials: W
authors.lastname: Rutkowski
authors.affiliation: Department of Mechanical and Aerospace Engineering, The George Washington University, Washington DC.
authors.forename: Nicholas V
authors.initials: NV
authors.lastname: Batista
authors.affiliation: Dian Fossey Gorilla Fund International, Atlanta, Georgia.
authors.forename: Felix
authors.initials: F
authors.lastname: Ndagijimana
authors.affiliation: Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington DC.|Division of Mammals, National Museum of Natural History, Smithsonian Institution, Washington DC.
authors.forename: Shannon C
authors.initials: SC
authors.lastname: McFarlin
keywords: distance meter; gorilla; parallel laser; photogrammetry