Biologists in New Hampshire have uncovered a massive threat facing local moose populations, and it only appears to be getting worse. According to a report from the Portland Press Herald, a tagging project reveals that an unfortunate number of moose calves are dying from a nearly invisible menace; ticks.

Preliminary figures suggest that nearly 75 percent of moose calves tracked by the study have died as a result of exposure to ticks. New Hampshire biologist Kristine Rines reports that this is the second year in a row with such high mortality rates for moose calves.

“It doesn’t bode well for moose in the long term if we continue to have these short winters,” said Rines. As the winter season ends earlier in the year on average, ticks are getting a few extra weeks to establish their presence in New Hampshire forests and feast upon the vulnerable moose calves.

Just last year, the state saw 20 out of 27 tagged moose calves deceased by the end of April, compared to only 13 out of 22 the previous year. “As moose numbers decline, the ticks will decline, as well. What we don’t know is at what point things well level off,” Rines said.

The study, which began in 2014, is projected to span a six-year period. Scientists in both New Hampshire and Maine hope that they can determine the underlying causes behind the moose decline and begin efforts to conserve the population, but saving the animals is far from a sure bet at this point.

Maine has the largest moose population in the lower 48 states. Moose calf mortality dropped last year from 73 percent to 60 percent, and mortality for adult moose fell from 33 percent to 8 percent over the same period. Still, the problem of winter ticks takes a heavy toll on moose.

“We’ve got a long way to go before we’ve got specific answers, but we’re trying,” said Rines.

A press release from the state of New Hampshire describing the details of the study can be found here.