Testing a non-invasive field method to measure body size in wild gelada monkeys – UROP Spring Symposium 2021

Testing a non-invasive field method to measure body size in wild gelada monkeys

Priya Varshika Ganji


Pronouns: she, hers, her

Research Mentor(s): Sharmi Sen, PhD Candidate
Research Mentor School/College/Department: Anthropology, College of Literature, Science, and the Arts
Presentation Date: Thursday, April 22, 2021
Session: Session 6 (4pm-4:50pm)
Breakout Room: Room 11
Presenter: 6

Event Link


Across the animal kingdom, body size is known to influence male-male competition and affect male reproduction. However, for several long term animal research studies, estimating body size in the wild through non-invasive methods is not always straightforward. Here, we develop and validate a non-invasive field method to measure body size of wild gelada monkeys (Theropithecus gelada) – a close relative of baboons that are endemic to the Ethiopian highlands. Using digital photogrammetry, we analyzed photographs to measure the maximum lengths of the distal forelimbs and hindlimbs from 67 individuals. We collected 620 photos in total along with actual morphometric measurements using a tape measure from 2019-2020. All photographs were measured using Adobe Photoshop by two researchers independently to account for observer bias. Mean intraobserver coefficient of variation (CV) was 2.74% and mean interobserver CV was 4.67%. CV for distal limb segment measurements obtained from digital photogrammetry and actual measurements was 4.05% and for the distal forelimb and 4.04% for the distal hindlimb respectively. Actual measurements of both distal forelimb and hindlimb lengths were positively correlated with overall body weight of the monkeys (ulna – r = 0.82, t = 21.574, df = 222, p <0.01*; tibia - r = 0.67, t = 13.551, df = 230, p <0.01 *). Measurements obtained from digital photogrammetry were also positively correlated with body weight (ulna - r = 0.57, t = 10.5, df = 230, p <0.01 *; tibia - r = 0.60, t = 10.642, df = 202,p <0.01 *). Although these values were less correlated than the actual tape measures, we believe these distal limb segment lengths can be used as a reliable proxy for estimating body weights in geladas. Future investigation into how these variables differ between the two sexes and across different age groups will provide useful information on the developmental patterns in geladas as well as allow us to quantify variation in body size within a population. Authors: Priya Ganji, Sharmi Sen, Jacinta Beehner
Research Method: Data Collection and Analysis

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