Mining morphometrics and age from past survey photographs

Frontiers in Zoology - Tập 16 - Trang 1-11 - 2019
Caitlin E. Black1,2, Hannah S. Mumby1,3,4,5,6, Michelle D. Henley5,7
1Bull Elephant Network Project, UCCRI, Department of Zoology, David Attenborough Building, Cambridge, UK
2Present address: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
3Wissenschaftskolleg zu Berlin, Berlin, Germany
4Centre for African Ecology, University of Witwatersrand, Johannesburg, South Africa
5Applied Behavioural Ecology and Ecosystem Research Unit, Florida Campus, University of South Africa, Johannesburg, South Africa
6School of Biological Sciences, University of Hong Kong, Hong Kong SAR, China
7Elephants Alive, Hoedspruit, South Africa

Tóm tắt

Researchers often document wildlife surveys using images. These images contain data that can be used to understand alterative research objectives, even years after they were originally captured. We have developed a method to measure age and morphology (body size measurements and tusk size) from survey image databases and future surveys, without the availability of a known subject distance or a scale in each image. African savanna elephants (Loxodonta africana) serve as an ideal model species to develop a non-invasive, image-based morphometric methodology: as handling these animals is particularly invasive and expensive, involving anaesthesia and because of their IUCN ‘vulnerable’ status. We compare in situ measurements, taken during collaring events, to tusk-to-body-size ratios, measured from the images. We provide evidence that relative morphological measurements, musth timing, and age of male African savanna elephants can accurately be obtained from a survey image database of over 30,000 images, taken over an 18-year period. Of the 11 tusk to body size ratios calculated, we recommend the use of two in particular for future measurement in African elephants to determine size and age: 1) tusk length to tusk diameter and 2) tusk length to body height. We present a practical, non-invasive measure to estimate morphometrics, including both age and tusk size from photographs, which has conservation applications to the protection of elephants and is relevant to a range of other taxa.

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