Estimating the age of western grey kangaroos (Macropus fuliginosus ocydromus)
Chris Mayberry A D , Roberta Bencini A , Peter R. Mawson B and Shane K. Maloney CA School of Animal Biology, The University of Western Australia, Stirling Highway, Crawley, WA 6009, Australia.
B Perth Zoo, 20 Labouchere Road, South Perth, WA 6151, Australia.
C School of Human Sciences, The University of Western Australia, Stirling Highway, Crawley, WA 6009, Australia.
D Corresponding author. Email: c.mayberry@ymail.com
Australian Mammalogy 40(2) 254-261 https://doi.org/10.1071/AM16058
Submitted: 28 November 2016 Accepted: 9 October 2017 Published: 23 November 2017
Abstract
Scientific studies and population management may benefit from knowledge of the age structure of a target population. We evaluated traditional and newly developed methods of estimating the age of kangaroos with data from 336 western grey kangaroos (Macropus fuliginosus) culled from a wild population in south-western Australia. We compared their ages based on molar progression with data on head, leg, and foot length, a balanced sum of all three measures, dried eye-lens weight, and molar wear score, and derived formulae to estimate age from each variable. Molar wear score has a linear relationship to molar progression and therefore leads to similar estimations of age, but requires only one complete arcade of molars. Because the relationships between age and the lengths of head, foot and leg are curvilinear, these become less reliable indicators of age with increasing age but the accuracy can be improved by considering a combination of the lengths of head, foot, and leg. Estimation of age from dried lens weight is more accurate than estimation from morphometry. The use of morphometry to estimate the age of kangaroos older than two years is more reliable than previously thought and requisite data can be collected from live animals. Where lethal methods are needed to collect samples, a largely intact skull, a single arcade of molars, or the lens extracted from one eye can reliably be used to estimate age.
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