Abstract:
Darwin’s theory for the evolution of the long neck of giraffes is that height confers access to browse free of
competition from smaller browsers. The theory predicts that survivors of a drought will be the tallest
animals in a population. All studies so far have tested this hypothesis by analysis of feeding patterns and
behaviour.We have studied it by analysing the demography of deaths in a drought. Using skeletal material
from 26 giraffes that died as a result of a drought in southeastern Zimbabwe in 2008, we established the
body mass, height, and age of the dead giraffes using allometric equations developed from culled animals.
Typical giraffe populations consist of 55% adults (>6 years old), 15% young adults (3–6 years old), 15%
juveniles (1–3 years old), and 15% neonates (<1 year old). Skeletons came from 54% adults, 14% young
adults, and 32% juveniles. No neonatal skeletons were found. More juveniles died than expected because
they have to compete with other browsers for nutrients. Most adult deaths occurred in the tallest and
largest males because their daily requirements for browse are highest and could not be met by the amounts
available at any level. Thus the survivors of this drought were young adults, a finding contrary to the
predictions of Darwin’s feeding hypothesis.
