UP TO 500 flying foxes died at Yarra Bend Park yesterday after the extreme heat decimated the colony.

Animal rescuers are tending the animals on both the Boroondara and Darebin sides of the river, with rescuers describing the sight as "horrific".

The South Oakleigh Wildlife Shelter's Michele Phillips said the extreme heat had caused the creatures to literally "drop out of the trees".

>> The Oakleigh Wildlife Shelter, run by volunteers, urgently needs donations of Lectade rehydration fluid, apples, grapes and corn. To donate phone 0411 600 591.

"It's a nightmare. We lost so many yesterday," Ms Phillips said.

Rescuers are rallying at the Kew park with water spray and rehydrating fluid, trying to save thousands of remaining flying foxes.

"When they drop to the ground we are trying to rehydrate them, and we are spraying the ones still in the trees," Ms Phillips said.

Victorian Advocate of Animals spokesman Lawrence Pope said rescuers were finding many dead animals, and others barely alive.

"I just had one instance where I saw a mother trying to revive her baby and the baby literally died while I was standing there," Mr Pope said.

"It's completely due to the heat. The animals can't cope, especially the young ones."

Mr Pope said Parks Victoria and the Department of Primary Industries staff had joined the rescue mission and clean up.

"I think we've managed to save as many as we've found dead," Mr Pope said.

"Spraying (is) keeping the animals cool, but it is a delicate balancing act and we have to use our judgment as we don't want to disturb the colony too much."

"We will have people here over the next three days continuing to monitor the situation."

Ms Phillips, a wildlife rescue volunteer, said she was caring for about 70 heat-stressed animals and birds.

She said she had been inundated with calls from residents across Melbourne's southeast, including Bayside and Glen Eira, with heat-stressed wildlife, and in the last 24 hours had collected dozens of ill animals and taken them to vets.

"I have possums in every room, and brought all my birds from my 15 aviaries inside," Ms Philips said.

She appealed to people to put bowls of water outside for wildlife, and shade their gardens.

"If you find (wildlife) on the ground, put them into a box, try to give them water and ring me," she said.

She urged people not to hose down animals and birds, as it would stress them too much.

The shelter is at 23 Murumba Ave, Oakleigh South. If you have heat-stressed wildlife needing medical treatment, call Ms Philips on 0411 600 591.