Biodiversity in a Pellet

15 March 2013

The South Australian Museum is tracking the biodiversity of our outback wildlife species in a curious manner – by studying regurgitated food pellets from owls.

A dedicated team of experts and volunteers has been working on the project for many years and has identified new species to help the South Australian Government design better conservation programs. By analysing the indigestible material in the pellets, the team has provided a clearer picture of which rodents, marsupials, birds, reptiles, frogs and arthropods live where, and how they fit into the food chain of the ecosystem.

For small mammals, the skull or skull fragments with teeth are the telltale items for identification. The team has even been able to study the impact of drought on species populations, without actually collecting live animals.

Sifting through animal remains in regurgitated pellets may not sound glamorous, but it's something our Subfossils Honorary Research Associate and the project leader, Graham Medlin, is incredibly passionate about. He heads the dedicated team which gathers every week to pull apart the regurgitated material to find creatures' remains and articulate their skeletons.

The regurgitated pellets contain the bones, fur, feathers, scales and insect exoskeletons from the owl species, which cannot be broken down by the its digestive system. Many small animals are eaten whole, so the entire skeleton is often regurgitated in each pellet. Larger prey species, such as rats, are decapitated and dismembered. Ten to twelve hours later the indigestible material is regurgitated as a fur — or feather-wrapped pellet coated in slimy mucus, to assist its passage out through the gullet. When dry and fresh, the pellet has a black, varnished appearance.

While the most common pellets dissected come from Barn Owls, the volunteer team also dissect pellets from Grass owls, Wedge-tailed Eagles, Letter-winged Kites, Black-shouldered Kites, Kestrels and Boobook Owls.

Mr Medlin was a high school science teacher and in 1976, took his students to Chambers Gorge in the Flinders Ranges. "Some students found bones in caves and they came back to me and said, 'what is this'? – and I didn't have a clue what they were. I took them into the South Australian Museum to have them identified and they said 'you've got rare and extinct species in there'!"

Overwhelmed by curiosity, Mr Medlin returned to Chambers Gorge in his own time and spent the next ten years climbing in every cave and hole, collecting hundreds of whole barn owl pellets and thousands of loose bones from pellets which had fallen apart after insects had eaten the fur.

"Because two schoolboys happened to have climbed into a cave and pulled out some bones, the biodiversity of the Flinders Ranges became a lifelong obsession for me," he said. "It also happens to be one of the the best sites for subfossil material in South Australia."

Mr Medlin used the South Australian Museum's collections and staff support to develop his expertise in the identification of the material, before people heard about his work and started sending him owl pellet specimens. He then developed an educational course at his school to teach children about the process of identifying bones in pellets.

Through the Museum's Senior Researcher in Mammals, Dr Cath Kemper, Mr Medlin was awarded a contract position to identify the material collected from Chambers Gorge. In 1991 he was appointed an Honorary Research Associate. Following on from his 20 years of field work with students at Chambers Gorge, he wrote a book on the natural history of the area.

After retiring from teaching, Mr Medlin continued his quest for illustrating the biodiversity of our State through the Museum, setting up a research laboratory for the project with the help of Dr Kemper and attracting enthusiastic volunteers.

"Some of them wouldn't miss it for the world, they have so much fun," he said.

The process of sifting through the pellet material can be complicated and time consuming – so good company and a sense of humour is necessary.

"First the pellets are numbered and stored in egg cartons. They're measured to the nearest millimetre, weighed and then washed to cleanse them of the mucous coating that comes from the owl. We use fine forceps to take out bones such as the skull, limbs, scapulae and pelves."

The fur is dried separately and usually only kept if it has come from a new or extinct species.

"The volunteers are carefully trained to identify the species bones present in the pellets. There are three stages of sorting to actually remove all of the bones and material, before we can discover and record what the owl has eaten."

Identification of species through owl pellet analysis is not unheard of, but is not especially common either. So why collect and sift through pellets, rather than collect live specimens?

Mr Medlin cites one scientific study he has been involved in as a classic example of what extra insight this method offers.

"An employee from Santos who had been working on an oil gas well south of Moomba came in and said he'd found a Barn owl roost between two buildings. He brought the pellets in and I said 'look, this would be a really interesting project, can you collect the pellets over 12 months'? For the first time that I'm aware of in Australia, we had a timeline on the collection of pellets and what animals were in them."

The collection happened to occur at the tail-end of a drought, when there was virtually nothing else for the owls to eat except reptiles – mainly geckos.

"Then the rains came and the rodent population went up, and the whole population was blooming," said Mr Medlin. "We were able to use the owls to analyse what small mammals were there, and their breeding cycles, as well as birds and frogs. It's a remote area so you're not going to get too many biological surveys being carried out there over a 12-month period. The barn owls could tell us everything we needed to know!"

With the assistance of Fauna Survey Officers from the Department of Environment, Water and Natural Resources, and other volunteer biological survey groups, the South Australian Museum plans to continue similar projects to provide a clearer and broader picture of our biodiversity – and the opportunity for volunteers to learn about science in a stimulating and enjoyable way.