Growth and development of the koala from birth to weaning
Blanshard, WH 1991, in Lee, AK, Handasyde, KA & Sanson, GD (ed.), Biology of the Koala, Surrey Beatty and Sons, Chipping Bay, pp. 193-202.
Several observations of the developmental changes in the physical appearance, dentition and behaviour of koalas during the 12-month period from birth to weaning have been compiled and documented.
Like all marsupials, koala joeys are underdeveloped at birth. Within the first 12 months of life, a koala develops most of its adult physical attributes and subsequently gains independence from its mother. Previously, little information had been published about the developmental timeline of the juvenile koala within this initial 12-month period. Here, Blanshard combines her own observations of hand-raised koalas with those documented by others to describe the typical developmental stages of the juvenile koala.
Koalas were first seen to emerge the head from the pouch at a mean of 182 days of age and emerged totally from the pouch at 201 days. Juveniles first consumed maternal faeces or ‘pap’ at a mean of 198 days and subsequently eucalypt leaves at 216 days. The average age at which koalas were first seen to briefly part from their mothers was 252 days. Several changes in the physical appearance of juvenile koalas over their first seven months of life were documented such as the opening of the ears and eyes, development of hair, pigmentation of the skin, and definition of the pouch or scrotum, and bifurcation of the tip of the penis. Primary ‘milk’ teeth are present in juveniles ranging from 79- to 151-days old which are suggested to have no function and absorb before cutting the gum, but may in some cases be retained to adulthood. The breaching of the gum line by the premolars and in some cases second molars probably aligns with the consumption of maternal faeces, while the emergence of the fourth premolars likely coincides with the first consumption of leaf. Regarding juvenile behaviour, ‘play’ is loosely defined as an activity that appears to serve no function. These activities may be social, such as wrestling or biting another juvenile, object-oriented, such as sensory exploration of surroundings, or locomotor, such as repetitive or directionless movement. Play behaviours were observed in koalas at around 176 days of age. At 203 days old, koalas were able to grab and tear leaves with their incisors. In males, secretions from the scent gland were first observed at around 398 days of age.
The observations that served as the basis for these descriptions represent koalas from both captive and free-ranging environments. It was found that the developmental timelines of hand-raised and wild juvenile koalas are very similar. This publication is one of the first to systematically compile and document descriptions of the early growth and development of the koala, contributing to our understanding of the life cycle of this unique species.
Summarised by Joanna Horsfall
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