Page last updated at 08:41 GMT, Wednesday, 19 August 2009 09:41 UK

'Social networks' may help devils

By Mark Kinver
Science and environment reporter, BBC News

Tasmanian devil infected with DFTD (Image: Rodrigo Hamede)
The spread of DFTD threatens to wipe out the wild population of devils

Understanding how Tasmanian devils interact may help limit the spread of a disease that threatens to wipe out the wild population, a study has suggested.

Researchers used radio collars to log how often the normally solitary devils came into contact with one another.

Writing in Ecology Letters, they said the data could help shape measures, such as habitat management, to curb devil facial tumour disease (DFTD).

DFTD has had such an impact on numbers, devils are now listed as Endangered.

"A common problem that a lot of people studying wildlife diseases have is gathering good data," explained lead author Rodrigo Hamede, from the University of Tasmania.

"Because this is a directly transmitted disease, we needed to know as much as possible about devil behaviour and devil ecology."

He added there were a number of assumptions about how the devils interacted with each other that were not based on robust findings, but the information gathered by the collars provided the most comprehensive dataset to date.

The team fitted the collars, known as "proximity data loggers", on 46 sexually mature devils - 23 male and 23 female - in Narawntapu National Park, northern Tasmania.

The devices, which weighed 120g, were set up to record encounters of 30cm or less between two or more animals.

The team decided to use these parameters because DFTD required direct physical contact in order for it to be transmitted.

'Super-spreaders'

The researchers said there were a number of reasons why it was important to understand animals' social networks in order to take practical steps to tackle diseases in wildlife.

DEVILS IN DETAIL
Tasmanian devil (Getty Images)
Scientific name: Sarcophilus harrisii
Devils were given their common name by early settlers, who were haunted by "demonic growls"
Largest living carnivorous marsupial
Now only found in Tasmania
Can live up to five years in wild
Weight: male 10-12kg; female 6-8kg
They favour habitats where they can shelter by day and scavenge by night

"It is usually the case that a small number of highly connected individuals, often called 'super-spreaders', are responsible for the majority of disease transmission," they explained.

"If these individuals belong to identifiable sex or age classes, then management actions such as selective culling or targeted [treatment] may be effective in treating transmission."

The data recovered from loggers revealed a few surprises, said Mr Hamede.

"I was expecting to see much more male-to-male fighting," he told BBC News. "I suspect that this will have something to do with males guarding females."

He explained that devils' normal behaviour involved a male grabbing a female, taking her back to a den and preventing her from leaving - ensuring that he was able to mate with her.

"Our paper shows that 99% of encounters were male-to-female during the mating season. There were hardly any male-to-male or female-to-female encounters."

"Outside of the mating season, surprisingly female-to-female contacts were more prevalent," he added.

"This is probably as a result of devils having a matrilineal society in which females tend to stay in the area of birth and get the best location for food and rearing young.

Tasmanian devil in a trap (Image: Rodrigo Hamede)
We have a little bit of time to try to protect unaffected populations, which remain in only 25% of the state
Rodrigo Hamede,
University of Tasmania

"It was quite interesting to see that the role of the males was not that important within the devil's social network."

Mr Hamede said the data also showed that every animal fitted with a logging device appeared to be part of a bigger social network.

"These are solitary animals, meaning that they do not live in large social groups like lions or meerkats.

"But nevertheless, they are still social in the sense that they are coming into frequent contact, either as a result of competing for food or direct contact during the mating season."

Although the data showed that the extended network had a few individuals that had a higher than average number of contacts with other devils, the team was not able to identify a particular age-group or sex that could be targeted.

But it did highlight the importance of ensuring that currently unaffected populations remained isolated from the disease, they added.

DFTD was first described in the mid-1990s, when devils with large facial tumours were photographed in north-eastern Tasmania.

By the end of 2008, the disease - which kills infected animals within nine weeks - had been confirmed at 64 locations, covering more than 60% of the Australian island state's mainland.

Despite the bleak outlook, Mr Hamede said there was some hope for the long-term survival of the wild population of devils.

"We have a little bit of time to try to protect unaffected populations, which remain in only 25% of the state.

"I don't think we can stop the epidemic or do much apart from keep these populations disease-free."

He added that much more attention had to be given to protecting the habitat of unaffected devils.

"Disease itself is very unlikely to cause extinction in any species, but when we combine such a devastating disease as DFTD with degradation of habitats, fragmentation, etc, then the outlook for the devils' future is not a very nice one."



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