ISLE ROYALE, Mich. - One of four wolves captured in Minnesota and relocated to Isle Royale in Lake Superior has died, and National Park Service scientists say they don't know why.

The wolf was one of four trapped on the Grand Portage Indian Reservation in late September and early October and moved to Isle Royale to help bolster the island's fading wolf population.

Wolves are very territorial and will often kill other wolves from outside their pack, but that apparently did not happen in this case.

“There was no obvious cause of death and no indication of wolf-on-wolf mortality,’’ the Park Service said in a report released Tuesday.

All the transplanted wolves have been fitted with a GPS collar that, if working properly, tells scientists where the animals are moving and, if it stops moving for many hours, that it is likely dead. But the collar on this wolf malfunctioned and wildlife biologists on the island were forced to track the wolf down to find the body.

Park Service officials earlier killed and cached several moose on the island to make sure the newly arrived wolves had ample food to get them through the relocation process. The Grand Portage wolves were picked because they were close by and because they already know how to survive on moose, which can be difficult for a single wolf to bring-down.

The deceased wolf is being transported to the U.S. Geological Services wildlife health lab in Madison, Wis., for a necropsy. Results are expected in December.

The three remaining relocated wolves “are doing well and their movements are being tracked through GPS. They have occasionally been within 700 feet of each other while exploring the island,’’ the Park Service said Tuesday.

The wolf is the second involved in the relocation effort to perish. Another wolf captured in Minnesota died during the process.

Isle Royale park officials also confirmed Tuesday that they will attempt to trap several more wolves in Ontario, possibly from other Lake Superior islands, and bring them to Isle Royale in January. Trapping in Minnesota and Michigan for additional wolves would likely continue later in 2019 as the Park Service attempts to bring up to 30 wolves to the island over two or three years.

Scientists with Michigan Technological University, who have been studying the island's wolf and moose populations for 59 years, have said for years that the wolves need new blood or they face extinction.

Because of diminished and less frequent ice buildup between the North Shore and the island, as winters continue to warm across the Northland, no new wolves have wandered to the island and stayed for decades. That’s caused heavy inbreeding among island wolves, which spurred both physical and reproductive genetic deformities that have helped lead the wolf populations’ demise. The last two wolves, a father-daughter duo that are also siblings, have been unable to mate, meaning the island’s national wolf population is doomed. That's why Park Service officials earlier this year finalized the plant to bring new wolves to the island to help control the burgeoning moose population there.

The 45-mile-long, 143,000-acre island is about 14 miles of Minnesota’s North Shore. It’s mostly dedicated as federal wilderness.

Wolves are relatively new to the island, having crossed the ice in the 1940s. Their numbers reached a high of 50 in 1980. Wolf numbers on the island crashed from 24 as recently as 2009 to just the current pair, a 7-year-old female and 9-year-old male.

Moose came to the island much earlier in the 1900s, peaking at 2,445 in 1995 and hitting bottom at just 385 in 2007. In their annual survey last winter, scientists estimated the moose herd had grown to about 1,600 on the island.