Observations of Wood Bison Swimming across the Liard River, Northwest Territories, Canada

Abstract

We observed a group of 18 wood bison, of mixed sex and age classes, swimming across a 1.7 km wide section of the Liard River on 16 July 2002. Water levels and flow rates were above the long-term average for that time of year, and there was a river current of 14-16 km/h. The animals took at least 27 minutes to negotiate their 3.6 km swim. Younger animals were able to keep more of their head and body above the water level than older mature males. Calves of the year, observed swimming across a secondary channel of the river on 15 July 2003, had only their heads above water. Bison are capable of swimming across lakes and rivers (Wood Buffalo National Park, Yellowstone National Park), but well-documented cases of bison navigating rapidly flowing northern rivers are rare. Open-water crossings of the Liard River are important to the ecology of the Nahanni wood bison population, especially since seismic activity in the Liard River Valley is likely to increase.