WILDLIFE rescuers fear a toxic and still unconfirmed poison may spread through the food chain at Dubbo after a grim new discovery yesterday.
Two raptors were located "barely alive" at Troy Reserve among the bodies of dead cockatoos and corellas.
They were rushed to Taronga Western Plains Zoo for medical attention as more winged-bodies were found at a new site and the death toll reached an estimated 500 birds.
The discovery of the raptors, confirmed as whistling kites by the zoo, was a blow to those hoping to contain the carnage and heightened the urgency to find the source of the suspected poison.
"For the first time, we have come across two adult eagles that have ingested the toxins," WIRES representative Anna Felton said.
"It is imperative that the source of this pesticide is found so that appropriate steps can be taken to eliminate the impacts of native wildlife.
"If it proves that the poison is being passed down through the food chain, this could be devastating for a number of other species including snakes, tawny frogmouths and raptors."
WIRES Dubbo volunteer bird coordinator Helen Swan reported the latest rescue from Troy Reserve by a WIRES rescue van sent from Sydney with three employees in response to the outbreak.
"The thing that's really upset me today is the raptors," she said.
"It's shocking to think we as human beings can do this to a lovely bird.
"I'm not sure where it will end."
Dubbo City Council rangers and Ms Swan also attended a new site on Boothenba Road where dozens of dead or dying little corellas and a dead peewee were found, and were later yesterday still being collected from the site.
The NSW Environmental Protection Authority (EPA) first confirmed it was investigating the death of the large number of sulphur-crested white cockatoos, galahs and corellas on Thursday.
"It's shocking to think we as human beings can do this to a lovely bird. I'm not sure where it will end."
Initial laboratory tests indicated the native birds may have died as a result of pesticide exposure and yesterday the search for answers continued.
"The investigation including testing at the EPA laboratories in Lidcombe, is ongoing," NSW EPA north director Gary Davey said.
"If anyone has any information about the bird deaths or information about pesticide misuse, they should contact the EPA's EnviroLine on 131 555."
The two whistling kites joined other patients in the zoo's wildlife hospital.
"The birds presented with similar symptoms to the corellas we have received over the past week and both birds are on the same treatment," zoo spokeswoman Mandy Quayle said.
"It is still very early but we are hopeful that they will recover."
Ms Swan estimated that between 30 and 40 had been saved in past days.