Growth of Grey Kangaroos and the Reliability of Age Determination from Body Meausrements I. The Eastern Grey Kangaroo, Macropus giganteus

Abstract

Measurements of bodily parts were taken throughout life from captive male and female eastern grey kangaroos of known birth date. For each body measurement a growth curve was fitted, and confidence intervals calculated for determining the age of any new animal. A change of phase in the growth curve was apparent at the time when the young vacate the pouch. A join point in the curve was empirically estimated to occur at approximately 310 days, and the growth curve was represented by a 4-parameter non-linear model consisting of two hyperbolas constrained to pass through this common point. Tables presented permit determination of age from body measurements with corresponding confidence intervals for both males and females at 30-day intervals in the first year and less frequent intervals for the age of 15-36 months. Head and leg lengths proved to be the most reliable criteria for age determination; arm and foot length were reasonably accurate; ear length, tail length and weight were unreliable criteria.