Age determination in the platypus (Ornithorhynchus anatinus) using spur sheath and spur developmental stages: a review

Abstract

Reliable techniques and criteria for identifying sex and age class are important to understand the population biology of species in the course of wildlife research and monitoring. In platypuses, males have a keratinous spur on the inner surface of the ankle on each hind leg that undergoes characteristic age-related morphological changes within the first 3 years of life. Females, in contrast, do not develop a spur but instead develop a vestigial spur sheath that is lost toward the end of their first year. Spur developmental stages can be used to assign male platypuses to three age categories: ‘juveniles’ (≤12 months old), ‘sub-adults’ (13–24 months old) and ‘adults’ (>2 years of age), which are capable of breeding. Male spurs grow from a mean length of 12.4 (±0.5) mm after emergence from the nesting burrow to 18.6 (±0.6) mm by the end of the first year of life in Victoria. Platypus age categories have at times been inaccurately assigned. Here, we present an annotated pictorial guide of these age categories, suitable for use by wildlife rescuers and researchers in a field setting, and in veterinary surgeries, to facilitate accurate identification by those not familiar with this aspect of platypus biology.