At least 20 Andean condors have been poisoned in the mountain range between Chile and Argentina and two of the endangered birds have reportedly died.
Authorities suspect the condors -- which have 10-foot wingspans and can effortlessly glide through the air for hours without stopping -- were poisoned by an agricultural pesticide used to intentionally kill other animals in the region.
"The hypothesis is that they suffered organophosphate poisoning after they were exposed to insecticides used for agriculture," Eric Savard, a veterinarian involved in the birds' treatment, told The Associated Press.
Hikers crossing the Andes from Santiago, Chile, to Mendoza, Argentina, reportedly saw the condors behaving erratically, flying low to the ground and crashing into rocks on the mountainside. Witnesses say the birds were unable to take to the air after crashing and were seemingly dizzy and foaming at the beak, according to the BBC.
The poisoned birds were taken to a veterinary clinic in the city of Los Andres and will be held there until completely recovered, which is expected to be about 10 days.
Pablo Vergara, regional director of Chile's agriculture and livestock service, said the birds will then be taken to Santiago's Metropolitan Zoo for further care, and later released in the same area where they were found, Al Jazeera reported.
"[The poisoning] seems to have been caused by the ingestion of an ill animal or one that ate another being with some phosphorate compound," Vergara said.
In the same mountainous area where the sick birds were discovered, two dead foxes and a dead cow were also reported.
The Andean condor is one of the biggest species of bird on Earth and is considered a regional symbol.
Only a few thousand of the birds exist in the wild.