Turtles prefer the 'city life'

Jody Bourton, BBC News 21 Oct 09;

Urbanisation has long been at odds with wildlife.

However, scientists have found a turtle that does better in a suburban habitat than it does in nature reserves.

Eastern long-necked turtles living in the suburbs of Australia have larger home ranges and cope better with periods of drought.

The reptiles also appear to grow and survive better, suggesting suburban environments may sometimes be superior places to live than natural ones.

Scientists have published the findings in the journal Biological Conservation.

Eastern long-necked turtles (Chelodina longicollis) are common across much of south eastern Australia.

Found in many freshwater habitats in the wild and in towns and cities, they are carnivorous, feeding on fish, frogs and crayfish.

However, throughout the world urbanisation can be damaging to many animals, resulting in loss of habitat and the disappearance of species.

So the researchers examined how the long-necked turtle responds to urban living and drought.

They did this by comparing turtles that lived in the suburbs of Canberra, Australia to those in adjacent nature reserves.

What they found surprised them.

"We expected suburban turtles to move around less than those on the nature reserves in response to the many threats that suburban turtles could encounter, but we found the opposite," says Dr John Roe, a member of the research team from the Institute for Applied Ecology at the University of Canberra, Australia.

"Suburban turtles travelled longer distances and occupied home ranges nearly three times larger than turtles in the nature reserves," he says.

Long-necked commuter

The researchers attached miniature radio transmitters to the turtles in each habitat and followed their weekly movements over the course of a year.

Both turtle populations made long journeys of up to two and a half kilometres between bodies of water.

"Given their extensive movements, we expected that suburban turtles would have a high rate of encounters with vehicles on roads, and thus fewer would survive," Dr Roe says.

"Despite this, suburban turtles did not suffer appreciably higher mortality than their counterparts on reserve lands, only one of our 36 radio tracked turtles was hit by a vehicle," he told BBC News.

Vegetated drainage lines and drainage culverts running under roads in the suburbs of Canberra protected the turtles.

"The vegetated drainage lines and culverts allowed the turtles to move about and use the landscape in normal ways, which reduced their exposure to urban threats and allowed them to avoid suffering from excessive road mortality," Dr Roe explains.

Suburban oasis

The turtles' responses to drought also surprised the team.

Turtles in the nature reserves responded to the drying up of the wetlands by estivating, lying dormant buried under leaf litter.

However, suburban turtles did not need to.

"Water bodies are often incorporated into urban design for the purposes of storm water removal and retention," Dr Roe says.

So "suburban water bodies remain flooded, allowing turtles to maintain aquatic activities throughout the drought."

That means turtles living in towns and cities are immune to the worst effects of prolonged drought, which can deplete wild turtles' energy and water stores.

"It appears that the suburban landscapes, despite their many challenges, may be higher quality habitats than nature reserves for turtles during drought," Dr Roe says.

Life in the suburbs

Dr Roe also has evidence suggesting that suburban turtles outperform their counterparts on nature reserves in other aspects of their life history.

"We have additional data that demonstrates higher population abundances, growth rates, and evidence of at least equivalent recruitment from reproduction in suburban turtles," he says.

Dr Roe hopes to continue the research to see if this trend is represented over the turtles' entire life span.

He also hopes to monitor the turtles' response to the frequent droughts that are gripping much of Australia whilst exploring how suburban areas, road design and urban planning may effect them.

"It would be interesting to determine whether well-designed urban areas hold any promise as long term drought refuges for some turtle populations."