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Journal of Zoology. Print ISSN 0952-8369

Growth and age determination of African savanna elephants
A. M. Shrader1Ã, S. M. Ferreira1w, M. E. McElveen1, P. C. Lee2,3, C. J. Moss3 & R.J. van Aarde1
1 Conservation Ecology Research Unit, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa 2 Department of Psychology, University of Stirling, Stirling, UK 3 AmboseliElephant Research Project, Nairobi, Kenya

Keywords Loxodonta africana africana; shoulder height; sub-Saharan Africa; Von Bertalanffy growth curve. Correspondence Rudi J. van Aarde, Conservation Ecology Research Unit, Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa. Email: rjvaarde@zoology.up.ac.za Current addresses: ÃTerrestrial Ecology Research Unit,Department of Zoology, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa; wDepartment of Statistics, University of Auckland, Auckland, New Zealand. Received 24 May 2005; accepted 14 November 2005 doi:10.1111/j.1469-7998.2006.00108.x

Abstract
Understanding the population dynamics of savanna elephants depends on estimating population parameters such as the age at firstreproduction, calving interval and age-specific survival rates. The generation of these parameters, however, relies on the ability to accurately determine the age of individuals, but a reliable age estimation technique for free-ranging elephants is presently not available. Shoulder heights of elephants were measured in 10 populations in five countries across southern and eastern Africa. Data includedshoulder height measurements from two populations where the age of each individual was known (i.e. Addo Elephant National Park, South Africa and Amboseli National Park, Kenya). From the known-age data, Von Bertalanffy growth functions were constructed for both male and female elephants. Savanna elephants were found to attain similar asymptotic shoulder heights in the 10 populations, while individuals inthe two known-age populations grew at the same rate. The Von Bertalanffy growth curves allowed for the accurate age estimation of females up to 15 years of age and males up to 36 years of age. The results indicate that shoulder height can serve as an indicator of chronological age for elephants below 15 years of age for females and 36 years of age for males. Ages derived from these growth curvescan then be used to generate age-specific population variables, which will help assess the demographic status of savanna elephant populations across Africa.

Introduction
Savanna elephants Loxodonta africana africana live in landscapes ranging from deserts to forests across Africa (Blanc et al., 2003). Populations apparently respond to variation in habitat quality through differences in age atfirst reproduction, length of calving interval and survival rates (e.g. Laws, 1969). To estimate these population parameters, the age of individuals within a population needs to be accurately estimated. Methods for determining the ages of elephants rely on changes in back length (Croze, 1972), shoulder height (e.g. Laws, 1966; Douglas-Hamilton, 1972; Jachmann, 1988; Lee & Moss, 1995) and hind footlength (Western, Moss & Georgiadis, 1983; Lee & Moss, 1995) with age. Rates of tooth eruption have also been used to estimate the age of dead or immobilized elephants (e.g. Laws, 1966; Sikes, 1966; Hanks, 1972a; Fatti et al., 1980; Jachmann, 1988). Only a few studies have assessed growth for elephants of known ages (e.g. Western et al., 1983; Lee & Moss, 1995). Not surprisingly, no study has relatedages to patterns and rates of tooth eruption on living free-ranging elephants. The
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original study of Laws and colleagues (Laws, 1966, 1969; Laws, Parker & Johnstone, 1975) on shot elephants in Uganda developed tooth-ageing techniques based on a number of assumptions about the population and its age structure. Studies from captivity and elsewhere have noted problems with the original age...