The nene has had a roller coaster ride trying to survive in Hawaii. The endangered state bird, which resembles the Canada goose, was abundant on the islands until habitat loss and hunting sent its numbers to near extinction with only about 30 birds estimated to exist by 1951, according to the U.S. Fish and Wildlife Service. Thanks to captive breeding programs, about 2,500 birds are estimated to be alive today.

But then there's cat poop. Toxoplasmosis results from infection with the parasite, one of the world's most common parasites, according to the Centers for Disease Control and Prevention. Infection in the wild is most likely to happen from swallowing the parasite through contact with cat feces.

According to John Platt's report for Scientific American, researchers studied the presence of Toxoplasma gondii, the protozoan parasite transmitted by domestic cats that causes toxoplasmosis in humans and wildlife and historically has caused mortality in native Hawaiian birds. The study was published in the Journal of Wildlife Diseases.

Study results showed the birds on the island of Molokai, the island that had “a conspicuously consistent presence of feral cats,” also had the highest rates of infection:48 percent, according to Scientific American. Infections rates were 23 percent on Maui and 21 percent on Kauai, where feral cat populations were lower.

Study lead author Thierry Work, a wildlife disease specialist with the U.S. Geological Survey, says while the parasite itself isn't a major cause of death, it could have behavioral effects, making the birds more prone to trauma.

“This research confirms earlier studies dating from the 1970s that this parasite is probably found in tropical island ecosystems wherever there are feral cats,” Work told the American Bird Conservancy. “Recent studies also suggest that animals and humans are more prone to trauma when infected with T. gondii. Trauma is the chief cause of death for nene, and infections with T. gondii may be making them more vulnerable, but confirming that will require additional studies.”

Hawaiian geese aren't the only animals threatened by the parasite. Past tests found the endangered Hawaiian crow and Hawaiian monk seals have contracted and died from T. gondii infections, too.

People may also be at risk from contracting the infection due to contamination from cat feces, says the American Bird Conservancy. The group points out that in addition to spreading disease, cats are non-native predators that kill native wildlife. A 2011 study published in Global Change Biology reviewed the impact of cat populations on at least 120 islands around the world and found that feral cats are responsible for at least 14 percent of global bird, mammal and reptile extinctions.

Mary Jo DiLonardo Mary Jo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.