The Big Bog was the last refuge for the lower 48 states' woodland caribou, which vanished in the 1940s. Although caribou survived in Minnesota for a century after they disappeared in Wisconsin and Michigan, many were killed for food by loggers, trappers, and homesteaders, while peatland drainage projects, farming, and fires damaged habitat. Settlement also created conditions that drew white-tailed deer and their deadly parasites to northern Minnesota. By the late 1920s, the Big Bog caribou band was considered the last resident herd in the U.S., and in 1928 it had dwindled to 13. A 1931 fire consumed 1,600 square miles of the Big Bog. In 1932 Minnesota established the 480,000-acre Red Lake Wildlife Refuge to preserve caribou and other big game, and in 1935 the Beltrami Island Resettlement Project began, relocating settlers, reducing poaching, and blocking drainage ditches. In 1938 ten caribou from Saskatchewan were brought to Ludlow Island, and the largest bull was taken by Caterpillar tractor to a fenced area south of Hillman Lake, where he joined the last three cows of the original band. In 1939 the remaining captive caribou were moved to the Hillman Lake enclosure. In 1940 four cows gave birth, but the last original cow died, probably of old age, and her remains were acquired by the Bell Museum of Natural History. In 1942 a food shortage prompted the release of all 15–20 caribou from the Hillman Lake enclosure. Aerial searches from 1946 to 1950 found no sign of caribou in their Big Bog range or the Hillman Lake area, though unverified reports since 1950 have mentioned tracks and fleeting glimpses near the Canadian border.