Why are the woylies all dying? Since 2001 the populations of these tiny Australian marsupials have mysteriously crashed by as much as 90 percent. The species, which had already been driven to near-extinction in the early 20th century, had been on the path to recovery after successful conservation efforts protected them from foxes and other introduced predators. The rebound in population was enough to see the woylies removed from Australia's threatened species list in 1996, but five years later their numbers once again began to precipitously decline.

Now we have a clue for the cause of the mass die-off. It seems that a majority of woylies—also known as brush-tailed bettongs (Bettongia penicillata)—have been infected by parasites called Trypanosoma. Similar Trypanosoma parasites cause Chagas disease and sleeping sickness in humans in South America and Africa. Although Trypanosoma protozoa were known to exist in Australia, scientists had previously assumed they were harmless to wildlife.

That may not be the case, according to research published this month in the International Journal for Parasitology: Parasites and Wildlife. Researchers tested both live and roadkill woylies and found that almost all bore one or more of three species, or clades, of Trypanosoma parasites. In areas with declining woylie populations, 96 percent of the animals were infected with what appears to be the worst of the three clades. Infected woylies displayed both tissue inflammation as well as evidence of damage to the heart muscles. Adriana Botero, a PhD candidate at Murdoch University in Perth and the lead author of the study, told ScienceNetwork Western Australia that these infections and tissue damage may make them more vulnerable to predators.

The researchers also studied nine other marsupial species and found the parasites on them, but of the tested animals only the woylies had significant infection levels.

Meanwhile, another new study quantifies exactly how bad the woylie decline has become. According to research published this month in Oryx, some of the worst-hit populations have declined by 95 percent. Other groups have completely disappeared.

Photo by S. J. Bennett via Flickr. Used under Creative Commons license