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Issue link: https://mag.outdoornebraska.gov/i/377644
OCTOBER 2014 • NEBRASKAland 23 abdomen. Within 24 hours, otters were released in the same location where they were trapped. The 18 otters that received transmitter implants were located two to four times a week between 2006 and 2009. Additionally, researchers followed the overnight movements of the nocturnal mammals on foot or by vehicle several times during both the winter and breeding season, noting their location every 30 minutes from the time they left their den in the evening until they denned up again the next day. Locating the animals was not always easy. The range of transmitters in any telemetry study is limited, but the size of the transmitters in this study limited their range under the best conditions. The terrain of the Platte River Valley, which may include several streams separated by sandbars or permanent islands, sloughs on the edge of the river and all bounded by riparian forest further limited the range to much less than could be detected from the nearest road. Using a boat or even canoe to track the animals from the water was often impossible due to low flows. The most limiting factor affecting transmitter range, however, was the fact that otters spend most of their time underwater or underground in dens. All things considered, the range was sometimes as little as 100 meters, and as a result, otters sometimes could not be located for days or even weeks. But they were located nearly 1,000 times in all, with half of those locations pinpointing exact den or resting sites. It was enough for Wilson to determine the home range – the area in which they spend the majority of their time – to be 2,000 to 5,000 acres, numbers similar to previous research in other states. "It basically consists, in our study, of 5 to 10 miles of the Platte River," he said. "And then they would pop over to any associated habitat, open water areas like old sandpits, oxbow sloughs or wetlands." Because they are not territorial, there was plenty of overlap in individual home ranges. Wilson had hoped to see what the otters did when the Platte dried out in the summer. Ironically, after drying up in more than one summer prior to the study, it didn't run dry again until after the field work was complete. But considering the study found that, within their home range, otters used sandpits, stock ponds and warmwater sloughs more than any other type of habitat available, it's not hard to imagine where they would go when the river did dry up. In other places where otters have been studied, primarily in the east, the rivers run much deeper than the Platte, Loup and other Nebraska rivers where otters are found. Even when those larger rivers are ice-covered in winter, otters can still access dens on the riverbank. With highly-variable water levels, the Platte is different. When flows are low in the summer and the depth no more than a few feet, otters can and do get around and find frogs, minnows, crayfish and carp to eat, Wilson said. But in the winter, when so much of the Platte is shallow or frozen, there are few places for otters to forage. "There is some running channel, but it may not be accessible because an otter is not going to chew through 6 inches of ice to get down to a little bit of water," he said. "During those times of the year, otters really need the open water of sandpit lakes and sloughs." Carp or stocked game fish found in many pits and ponds are another draw for the otter, providing a very dependable food source that is easier to hunt in winter or summer thanks to clear water. Beavers create dens in the banks of pits and ponds that are accessible year-round to otters, which typically do not build their own dens. That is just one aspect of a relationship between the two mammals that benefits otters more than beavers. The other is the dams beavers build, which create slack-water habitat in which otters can live and fish. Otters have no natural predators when they're in the water. Above it, studies in other states have found they may fall prey to coyotes, bobcats, foxes, domestic dogs, wolves, mountain lions, bears and bald eagles. So sandpits, with den sites, abundant food and cover, especially when iced Otter Sign Otter tracks are 2 to 3 inches wide and 2 to 4 inches long. Otter scat is full of fish scales. Otters may consume a fish on top of the ice, leaving the head behind. Otters run and slide on snow, leaving a Morse-code-like track. PHOTO BY BOB GRIER PHOTO BY ERIC FOWLER PHOTO BY ERIC FOWLER PHOTO BY ERIC FOWLER