Volunteer wildlife carer Jenny Bryant said there had been an influx of koalas to her Tyabb sanctuary, most of which came from Somers.

And a higher proportion of injured koalas brought to the sanctuary were dying than was usually expected, she said. About 15 have died in the past month.

With the number of koalas in Somers, Bittern and Balnarring declining dramatically, concerned locals are planning a "koala day" to alert residents and tourists to the increasingly desperate plight of the iconic marsupial. "They're dying like flies," Ms Bryant said.

Several factors have led to the drop in koala numbers, most of them linked to population growth and increased tourism.

Increased traffic was mowing down koalas on roads in unprecedented numbers said Somers resident Jasmine Wigley, a member of FOLKLAW – Friends of Local Koalas, Land and Wildlife – a group dedicated to saving the koala and which manages Somers Koala Reserve at the end of Beach Hill Avenue.

Other problems included attacks by domestic dogs, removal of eucalypt trees leading to the loss of habitat, and the erection of large, solid fences that stop koalas moving about and being able to escape from dogs. Ms Bryant said chlamydia (a bacterial infection that can cause blindness, pneumonia, urinary tract infections and reproductive tract infections in koalas) and a debilitating mange were also common among the koalas in her care.

She said koalas wandered from tree to tree in search of food and mates over an area covering several kilometres.

"Of course they just wander across the road like they were here first, because they were," she said.

Koalas prefer to eat the leaves of swamp and manna gums, but can feed on the foliage of about 27 species, including pine needles and a range of native bushes.

Ms Wigley said many Somers residents would support a reduced speed limit for local roads being considered by Mornington Peninsula Shire.

"A lot of people come here and don't realise we have koalas," she said. "We are asking people to slow down, especially at night, because koalas are nocturnal. And carry the phone number of a wildlife carer with you. And don't cut down those trees. One tree near here was cut down and afterwards, I noticed a koala with her baby coming to where the tree had been and sitting down and crying."

The koala day is planned for Somers in September.

Details: call Ms Wigley on 0438986099. To report injured wildlife call Wildlife Help on the peninsula on 0417380687.