American Bison - Buffalo Field Campaign

Table 6.2 Diets of wood bison at select locations within North American ecoregions.
Ecoregion Location Season
Northern
Forests
Subarctic
Boreal
Forests
Wood Buffalo
NP and Slave
Lake, NWT
and AB
MacKenzie
Bison
Sanctuary,
NWT
Nahanni
Population,
NWT
the snow, led to major die-offs of bison (Dary 1989). Thousands
of bison were drowned in floods that resulted from the spring
melting of large snow packs (Dary 1989).
Predation by wolves may have been a significant force, taking
the most susceptible age and sex classes at different times of
year. Wolves may have preyed heavily on bison calves (Flores
1991) and killed older solitary males (Dary 1989). However,
predation may have had little effect on large nomadic or
migratory herds of bison (Terborgh 2005). Wolves maintain group
territories and bear altricial young, traits that would have made
it impossible for wolf packs to sustain sufficient pressure on a
wide-ranging, mobile prey (Terborgh 2005). Grizzly bears killed
some bison, occasionally from ambush (Dary 1989).
Grasses
(%)
Prior to the availability of firearms, the small number of resident
humans, and their relatively ineffective hunting, limited the human
toll on bison. Pedestrian harvesting was mostly non-selective
and involved surrounding or driving of bison groups over bison
jumps (Flores 1991). However, by the late 17th century, firearms-
equipped tribes from the Great Lakes region began moving out
on to the Great Plains. At the beginning of the 19th century,
tribes with horses were beginning to exert pressure on plains
bison and select for breeding age females (Flores 1991). At the
same time inter-tribal warfare led to buffer zones that served
as refugia for bison (Flores 1991; Martin and Szuter 1999). By
mid-1800s, an estimated 500,000 plains bison were killed for
subsistence, and an additional 100,000 were killed for their hides
Sedges 1
(%)
Plant Type
1 Includes rushes (Juncaceae); 2 Lichens; 3 Equisetum spp.; 4 November/December is early winter, January/February is mid-winter
48 American Bison: Status Survey and Conservation Guidelines 2010
Forbs
(%)
Woody
Plants
(%)
Spring 16 81 1 2
Summer 24 59 8 8
Autumn 21 71 4 2
Winter 36 63 1
Spring 6 68 1 26
Others
(%)
Summer 11 53 2 28 6 2
Autumn 32 15 4 12 37 2
Winter 2 96 2
Summer 6 37 29 14 1 3
Autumn 19 58 7 12 4 3
Early Winter 4 16 37 10 4 33 3
Mid-Winter 4 2 89 4 3 2 3
annually (Isenberg 2000). Bison populations began to decline as
increasing numbers of cattle and horses began to compete with
bison for forage and water (Flores 1991; Isenberg 2000).
6.3.1 Population structure
Reference
Reynolds et al. 1978,
Reynolds. 1976 in Reynolds
and Peden 1987
Larter and Gates 1991
Larter and Allaire 2007;
Larter, N.C. unpublished
data
Both plains and wood bison can be classified into sex and
age classes based on body size and horn morphology. Free-
ranging calves are readily distinguishable from all other age
classes based upon pelage colour for the first three months
of life, but their sexes cannot be distinguished. Yearlings may
be distinguished from adults until about one and a half years
old, based upon body size and conformation, when examined
at close range. Sex can be determined in animals more than
two years old on the basis of horn morphology and head
shape (Bradley and Wilmshurst 2005; Komers et al. 1993), or
noting the presence or absence of a penile sheath, but again
this requires viewing from close range (Carbyn et al. 1998).
Komers et al. (1993) described criteria for distinguishing
between subadult (two to four years old), mature, and old
bulls based on body size and horn morphology. The results of
composition counts are frequently standardised as a ratio of
selected age and sex classes per 100 adult females (Caughley
1977). Typically, within polygynous species such as bison,
adult females are the most abundant class in a population
and directly determine the size of the youngest age class
(McCullough 1994). The presence of new calves in a population
is sensitive to the timing of the count relative to the calving