American Bison - Buffalo Field Campaign
American Bison - Buffalo Field Campaign
American Bison - Buffalo Field Campaign
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Table 6.3 Ratios of select age classes:100 females among plains and wood bison populations.<br />
Subspecies Location<br />
Plains bison<br />
Wood bison<br />
Henry<br />
Mountains,<br />
UT<br />
Slave River,<br />
NWT<br />
Mackenzie<br />
<strong>Bison</strong><br />
Sanctuary,<br />
NWT<br />
Mackenzie<br />
<strong>Bison</strong><br />
Sanctuary,<br />
NWT<br />
Mink Lake,<br />
NWT<br />
Wood<br />
<strong>Buffalo</strong><br />
(Delta Area),<br />
AB<br />
Period of<br />
Observation<br />
July or<br />
September<br />
weighted<br />
average<br />
1977–1983<br />
50 <strong>American</strong> <strong>Bison</strong>: Status Survey and Conservation Guidelines 2010<br />
Adult Sub-adult Sub-adult<br />
Male Female Male Female Yearling Calves<br />
54 100 43 53<br />
Summer 1978 32 100 4 1 7 35<br />
July 1993 78 100<br />
July,<br />
unweighted<br />
average<br />
1984–1998<br />
July,<br />
unweighted<br />
average<br />
1989–1998<br />
Spring<br />
unweighted<br />
average<br />
1989–1996<br />
1995). Wallows may serve as focal areas for anthrax spores,<br />
and more frequent wallowing by adult males may contribute to<br />
greater mortality among adult males than adult females during<br />
outbreaks of the disease (Gates et al. 1995). <strong>Bison</strong> have died<br />
falling into hot pools and bogs. Accidental drowning of whole<br />
herds of bison by falling through<br />
thin ice in spring and fall has been<br />
reported (Roe 1970; Gates et al. 1991).<br />
Once bison break through lake or river<br />
ice, they are generally unable to haul<br />
themselves out and become trapped<br />
(Carbyn et al. 1993).<br />
Droughts and severe winters, alone or<br />
in combination, have led to episodic<br />
over-winter mortality in the absence<br />
of wolf predation in plains bison of<br />
the YNP central herd (Cheville et al.<br />
Figure 6.2 Age and sex class structure of<br />
wood bison at Mackenzie <strong>Bison</strong> Sanctuary,<br />
Northwest Territories, assuming an equal<br />
sex ratio among calves and yearlings (Gates<br />
et al. 1995).<br />
100 22 41<br />
100 30 51<br />
100 20 36<br />
Reference<br />
Van Vuren<br />
and Bray<br />
1986<br />
Van Camp<br />
and Calef<br />
1987<br />
Gates et al.<br />
1995<br />
Larter et al.<br />
2000<br />
Larter et al.<br />
2000<br />
Carbyn et al.<br />
1998<br />
1998; Green et al. 1997). Episodic droughts reduce late growing<br />
season forage quality and increase the probability of wildland<br />
fires that reduce the amount of winter forage available (Frank<br />
and McNaughton 1992). Simulations indicate that over-winter<br />
survival of YNP northern range bison is most strongly influenced
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