|Author(s)||Megan K.L. Strauss|
This is a guide for estimating the age of Masai giraffes (Giraffa camelopardalis tippelskirchi) with noninvasive methods. Giraffes are commonly categorized into three age classes: calf (0 – 1 year), subadult (1 – 5 years) and adult (> 5 years). This categorization, though somewhat arbitrary, has its origins in giraffe life history. After birth, calves remain with their mothers for 12 – 18 months. Age at first reproduction varies but is usually around 4 – 5 for females and 7 for males. Maximum longevity is thought to be 22 – 30.
This guide adheres to this age categorization, but it also enables age estimation at a finer scale. Calves are pictured at several stages, and subadults are broken down into year-long age classes. Adult females are assigned to two maturity classes and adult males are assigned to three classes. Male giraffes can be aged more reliably than females due to conspicuous secondary sex characteristics (this is especially true for subadults and adults).
This guide focuses on age estimation using physical traits. Key traits used include ossicones (parietal horns), skull ossification (in particular, addition of secondary bone), body size and shape, relative length of neck to legs, and marking coloration. These are traits that are observable on live or photographed animals. Here, they are described qualitatively. Age-height values for Serengeti giraffes are also presented at the end of this guide for those able to obtain height data. Physical traits that would require sedation or a postmortem to evaluate, such as tooth wear, are not discussed here.
Giraffe subspecies display substantial morphological variation. For example, the median horn of female Reticulated giraffes is more prominent than that of female Masai giraffes. This guide is intended to be used for Masai giraffes only, especially populations in northern Tanzania. Data was collected in Serengeti National Park from 2008 – 2010. The breakdown of calves and subadults into finer scale age classes was achieved by extrapolating from known-aged individuals. The author is solely responsible for any errors in the material.
Keywords: Masai giraffe, Tanzania, age, development, Serengeti National Park
Author: Megan K.L. Strauss