LOS ANGELES (AP) — Only two of a flock of 15 wild Canada geese that landed and became trapped in the La Brea Tar Pits in Los Angeles in late July have survived after they were rescued and cleaned off.

Los Angeles Animal Services extricated the birds from the pits on July 31. More than half had died, but the seven that were still alive were given to International Bird Rescue, a nonprofit that specializes in rescuing and rehabilitating birds from oil spills. Of those, only two survived between transportation and rehabilitation operations.

After three washes for both and a chest graft for one, the two birds are on a steady track to healing. If all goes well, they will be released into the wild in about a month.

“It’s heartbreaking to see accidents like this occur,” said JD Bergeron, CEO of International Bird Rescue, in a news release. “Birds in a changing world face dwindling natural habitat and lack of habitat is a big problem for the wild animals that call Los Angeles home. It is natural for animals to become trapped in the tar, but in a huge city with little wildlife habitat, the lake can look very attractive to animals.”

Famously host to a statue of mammoths succumbing to the tar, the La Brea Tar Pits are an ice age fossil site in the middle of Los Angeles. They contain species that represent the last 50,000 years of Southern California life. Still today, the pit attracts and inadvertently immobilizes mammals, birds and insects like “flies on flypaper,” according to Bird Center’s statement on the incident.

Bird Rescue’s Director of Operations Julie Skoglund said the combination of the oil’s elements and the birds’ extreme stress were the leading causes in their deaths. The tar can burn the animals’ skin, restrict their movement and put them at risk of suffocation.

“Any amount of oil or contaminant completely destroys a bird’s waterproofing, and so the birds can succumb very quickly to the elements because they’re not able to feed properly,” Skoglund said.

The birds suffered from capture myopathy, a symptom animals in captivity experience through overexertion that can lead to metabolic and muscle issues. One bird broke its leg in the struggle, the group said.

“We always work to try to mitigate the negative effects of human interactions on wildlife. So as much as we can prevent those types of things from happening is what we’d hope for,” Skoglund added.

Natural History Museum Communications Manager John Chessler called the incident “unfortunate and distressing.”

“This particular situation is a rare occurrence, but animals occasionally getting stuck in the tar is a process that has been happening here for over 60,000 years,” Chessler said in an emailed statement.

Los Angeles is home to migratory and local flocks of Canada geese, but Skoglund said its unknown which flock the birds belonged to. But the International Bird Rescue has a permit to band their birds once they have healed as part of the U.S. Geological Survey’s citizen science project. The federal program consists of small, numbered metal bands that go around a bird’s leg. Anyone who comes across that bird, alive or dead, can enter the number into the survey and describe the animal, its status, location and circumstances.

“If they are released, we might hear about where they go after that,” Skoglund said.