Mysteries Of The Stumpy Lizard Revealed

Welcome to the unique world of the Australian stumpy-tailed lizard!

The stumpy is one of Australia's most distinctive and abundant lizards, and is common throughout the Australian mainland. It has an average length of 41cm and a diet of insects, snails, carrion, flowers and fruit.

New research at Adelaide University shows the female of the species endures quite an ordeal during pregnancy - so much so that its own life may be in jeopardy as it approaches full term. For the last four weeks of pregnancy they eat almost nothing, are unable to breathe properly and move very little, which means they find it hard to exercise, forage for food or escape predators.

Department of Environmental Biology researcher Dr Suzy Munns, who has been studying stumpies and other reptiles for the past five years, says the sheer size of baby stumpies by the time of birth is the main reason for the mother stumpy's problems.

"The first thing to realise is not all reptiles lay eggs, and that many lizards, including the stumpy, give birth to live young," she says. "Baby stumpies are very large, relatively-speaking - they are approximately 35% of the mother's body weight, which is very high in the animal world.

"Or in other words, if a human female was to give birth to a baby that was 35% of her body weight, it would mean giving birth to a child the size of an average six-year-old!"

This situation is not helped by the fact the mother stumpy's body - unlike humans and other animals - doesn't expand in size during pregnancy as her baby gets bigger. The average gestation period for a stumpy is between five and six months, and they give birth to one to four young.

This means the young are occupying an increasingly large portion of the mother's body cavity, which decreases the space available for the lungs and digestive tract. Dr Munns' research investigated the breathing of pregnant stumpies to see how their breathing changed due to their lungs becoming increasingly squashed.

"What I found was that their ability to breathe properly became less the further they went into the pregnancy, and in the last six to eight weeks before birth both breathing frequency and the volume of breath are reduced quite significantly."

Dr Munns also found the metabolic rate of pregnant stumpies decreases quite markedly in the last three months of pregnancy, and in particular the last four weeks, where they hardly consume anything.