Growth and Dispersal of an Erupting Large Herbivore Population in Northern Canada: The Mackenzie Wood Bison (Bison bison athabascae)

In 1973, 18 wood bison (Bison bison athabascae) were introduced to the Mackenzie Bison Sanctuary. The population has grown at a mean exponential rate of r = 0.215 ± 0.007, reaching 1718 bison >= 10 months of age by April 1987. Analysis of annual population growth revealed a maximum exponential rate of r = 0.267 in 1975, followed by a declining rate, reaching a low value of r = 0.013 in 1987. Selection predation on calves was proposed as a mechanism to explain the declining rate of population growth. The area occupied by the population increased at an exponential rate of 0.228 ± 0.017 sq km/yr. The dispersal of mature males followed a pattern described as an innate process, while dispersal of females and juveniles exhibited characteristics of pressure-threshold dispersal.

Population demography of Peary caribou and muskox on Banks Island, N.W.T., 1982-1992

The Peary caribou population (excluding calves) on Banks Island declined from 6 970 (± 1133) in 1982 to 897 (± 151) in 1991. The 1992 estimate was 1 005 (± 133). Percent calves in the population varied among years (range 3.2¬31.1%). Mean group sizes dropped from 5.0 in 1985 to a low of 2.0 in 1989 and 1991. Median group sizes were significantly larger between 1982 and 1987 than between 1989 and 1992 (P<0.001). Large post-calving aggregations prevalent on the NW portion of Banks Island in the early 1980's were absent by the 1990s. The muskox population (excluding calves), increased from 29 168 (± 2104) in 1985 to 52 959 (± 2240) in 1992. Percent calves in the population varied among years, (range 11.8-17.1%). These values may be underestimates, because calves are small and muskox groups sometimes form defensive circles in response to aircraft. Muskoxen were distributed throughout the island during all surveys; however, the greatest increase in density occurred in the southern parts of the island

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

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.Le 16 juillet 2002, on a observé un groupe de 18 bisons des bois, des deux sexes et de groupes d'âge divers, traversant à la nage une section de la rivière Liard large de 1,7 km. Le niveau d'eau et le débit fluvial dépassaient la moyenne à long terme pour cette période de l'année, et le courant fluvial y était de 14 à 16 km/h. Les animaux ont mis au moins 27 minutes pour négocier leur traversée de 3,6 km. Les plus jeunes pouvaient garder hors de l'eau une plus grande partie de leur tête et de leur corps que d'autres mâles plus âgés. Les veaux de l'année, que l'on a observés le 15 juillet 2003, durant leur traversée à la nage d'une branche secondaire de la rivière, n'avaient que la tête hors de l'eau. Les bisons sont capables de traverser des lacs et des rivières (parc national Wood Buffalo, parc national Yellowstone), mais on ne connaît que peu de cas bien documentés de bisons négociant la traversée de cours d'eau nordiques à courant rapide. La traversée des eaux libres de la Liard est importante pour l'écologie de la population du bison des bois de la Nahanni, en particulier si l'on considère que la prospection sismique va probablement augmenter dans la vallée de la Liard

Population demography of Peary caribou and muskox on Banks Island, N.W.T., 1982-1992

The Peary caribou population (excluding calves) on Banks Island declined from 6 970 (± 1133) in 1982 to 897 (± 151) in 1991. The 1992 estimate was 1 005 (± 133). Percent calves in the population varied among years (range 3.2¬31.1%). Mean group sizes dropped from 5.0 in 1985 to a low of 2.0 in 1989 and 1991. Median group sizes were significantly larger between 1982 and 1987 than between 1989 and 1992 (P<0.001). Large post-calving aggregations prevalent on the NW portion of Banks Island in the early 1980's were absent by the 1990s. The muskox population (excluding calves), increased from 29 168 (± 2104) in 1985 to 52 959 (± 2240) in 1992. Percent calves in the population varied among years, (range 11.8-17.1%). These values may be underestimates, because calves are small and muskox groups sometimes form defensive circles in response to aircraft. Muskoxen were distributed throughout the island during all surveys; however, the greatest increase in density occurred in the southern parts of the island