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Return of an Icon:
Plains Bison in the Canadian
Mixed-grass Prairie
Gates et al. IUCN American
bison: Status survey and
conservation guidelines,
2010
Map from:
World Wildlife Fund
Terrestrial Ecosystems
They classified 116
different Ecoregions
Plains Bison
occupied at least 46
of these
Plains bison were the
most widespread of
all North American
large mammals.
NORTHERN SHORT GRASSLAND
ECOREGION
Grasslands National Park
Why did Grasslands National Park re-introduce
Plains Bison to this mixed-grass prairie ecosystem?
1. To restore a natural grazing regime using bison as the
dominant herbivore.
2. To compliment, not replicate the grazing patterns on
surrounding lands.
3. To restore the inter-relationships between bison, wildlife,
vegetation and soil disturbance.
4. To provide visitors with the opportunity to bison on the
mixed grass prairie.
Grazing History
There is abundant evidence that this region was heavily used by bison
for thousands of years
By the 1870’s the last wild bison were gone
Grazing History
Val Marie was the northern terminus of the Chisholm Trail, which saw cattle
from Texas trailed north to markets in Canada
Grazing History
For over 100 years these ranchers were excellent stewards of the prairie.
As local ranchers retired and sold their land to Parks Canada,
GNP removed cattle and cross fences.
Grasslands National Park Establishment
The Larson ranch was purchased in 1987
All cattle were removed and prairie allowed to rest
With no grazing, a heavy layer of thatch built up, with a resulting change
in diversity of all species.
Upland grass is the habitat most impacted by the removal of large herbivores.
It is the habitat type where impacts from the return of bison will be most obvious.
Bison impact the ecosystem in three principle ways;
1. Disturbance
2. Direct Relationships
3. Indirect Relationships
Ecological Relationships
Winter
Pugging
Disturbance
Trails
Urine
Patch Grazing
Wallows
Manure
Ecological Relationships
Direct Relationships
External
Carcasses
Parasites
Internal
Predation
Parasites
Nitrogen deposition
Increased plant growth
Ecological Relationships
Indirect Relationships
White-tailed deer
White-tailed
Jackrabbit
Nuttall’s Cottontail
Black-Tailed
Prairie Dogs
Facilitative Grazing
Pronghorn
Mule Deer
Ecological Relationships
3rd Order
Relationships
Diverse niches
for insects
77 grasshopper
species in GNP
Shed hair
Nesting material
for birds
Diverse
niches for
microtines
Predators &
Scavengers
There are 26 species of birds that are “endemic grassland birds”. Nine of these require
habitat types that cannot be found in a homogenous landscape. These 9 species are
known as “obligate grassland birds”.
The mixed grass prairie of GNP has 35 mammal species, but of these, less than a
dozen are endemic to the mixed grass prairie.
Benefits of Bison Grazing
Increases heterogeneity of upland grass community
Changes in vegetation create opportunities for other species
A study by A.T. Finnamore, showed that there were 65 species of beetles in GNP.
The ungrazed prairie had 35 species while the grazed sites had 22 species of beetles.
The Return of Bison Enhances Habitat for Wildlife Populations That Are Endemic
To The Mixed Grass Prairie
Masked Shrew
Western Jumping Mouse
Northern Pocket Gopher
Grasshopper Mouse
White-tailed Jackrabbit
Swift Fox
Black-tailed Prairie Dog
Black-footed Ferret
Olive-backed Mouse
Canadian Toad
Great Plains Toad
Spade-footed Toad
Greater Short-horned Lizard
Plains Hog-nosed Snake
Prairie Rattlesnake
Blotched Tiger Salamander
Yellow-bellied Racer
Plains Garter Snake
Mountain Plover
Baird’s Sparrow
Lark Bunting
McCowan’s Longspur
Sprague’s Pipit
Long-billed Curlew
Ferruginous Hawk
Chestnut-collared Longspur
Loggerhead Shrike
How do bison create, or enhance the niches occupied by these prairie species?
Grazing Lawns
Grazing lawns are first established during the winter months
Bison select for the highest volume forage, and through cratering,
create a short grass sward within the tall grasses.
When spring arrives, these clipped patches green-up first.
Ungrazed
Grazed
Ungrazed
Grazed
FACILITATION
For other species
Average plains bison wallow density in EINP = 4.5 wallows / ha
Average ancient wallow density in GNP = > 30 wallows / ha
> 12 species of mammals, birds, herptiles observed using wallows
Vernal wetlands created by rain-flooded wallows – ideal habitat for many species
Prairie Dogs, Bison and the species that depend upon them
Bison graze the edges of prairie dog towns, keeping the grass short.
Short grass allows the dog town to expand in size
Prairie dogs are a Keystone Species; they provide habitat essential to the
survival of other species, such as;
Photo by Wendy Michael
Photo by R. Postma
Burrowing owls and bison dung
The dung serves several purposes;
It masks the smell of the owls, and in doing so protects them from predation. This is
known as “Olfactory camouflage”.
The presence of dung at a prairie dog burrow, serves to attract potential mates.
The dung regulates the humidity inside the burrow, releasing moisture in hot periods,
and absorbing it during wet periods.
Dung in the burrow reduces the level of carbon dioxide.
In one survey of 71 owl pellets, they found the remains of 2484 beetles, 7 sagebrush
voles, 3 deer mice and 11 unknown mircrotines; 19 grasshoppers, 2 bees, 1 brown
thrasher and 1 horned lark (Holroyd and Trefry 2000).
It attracts dung beetles and other insects, which the owls prey upon. A higher density of
beetles, at the tunnel entrance, allows chicks the ability to hunt near safety.
Burrows with dung have over 75% more insect biomass than those without dung.
Dung in and around the burrow informs other owls that this tunnel is occupied
– go somewhere else.
There are 3 behavioral types of
dung beetles;
1. The “Rollers” a male –
female pair who collect a
wad of dung, then roll it
to a place where they
bury it.
2. The “Tunnelers” take a
chunk and bury it in a
tunnel they make close to
the manure pat. These
two are known as
“nesters” because they
prepare a home for their
young, then bring food to
them.
3. The third group are
known as the “Dwellers”
– they live within the
manure patty and raise
their young right there
(Thomas 2009).
Bison Patties
An essential part of a healthy prairie
Bison defecate, on average, about 12
times per day
A herd of 150 bison creates about 1800
patties per day
Each bison patty covers about 0.422
square meters
Each patty weighs an average of about
1 kilogram
Each year about 28 hectares of prairie is
covered by bison dung.
Each year about 657,000 kilograms of
bison manure is deposited on the prairie
With the removal of bison from the landscape, the relationships between bison, owls
and beetles halted, and dung beetle populations must have crashed.
Under ideal conditions, dung beetles can bury all of the dung from a patty in less
than one week.
Some historical accounts from the 1800’s indicate that a summer bison patty would
disappear within three days. Winter patties supplied the bulk of the fuel used by
First Nations and early European explorers.
As the bison vanished from the prairie, so to did a host of species that depended upon
them, and the materials they left behind.
Mountain Plovers are an
obligate grassland bird
They require heavily grazed, short grass
to hunt for insects and to build their nests
Sharp-tailed Grouse
Prairie dog Predators
Johane Janelle
Many other species use dog towns
The Northern Pocket Gopher
– An Ecological Engineer
The Northern Pocket Gopher
Grazed prairie= increased forb diversity = increased Northern Pocket Gopher density =
- new tunnels for species such as salamanders, snakes toads, microtines
- more prey for avian and mammalian predators
- greater turn-over of soil nutrients
- improved aeration of soil
- improved subsurface movement of water
- seed bed for native plant establishment
- increased density and diversity of insects
- improved grazing for a variety of prairie herbivores
Ferruginous hawks are more specialized to hunt pocket gophers than other hawks, due
to their habit of stalking their prey, crouching or waiting at burrow entrances, or where
pocket gophers are actively moving soil to the surface.
An aspen parkland example of inter-species dependence on bison
Bison often deposit their patties near the forest / meadow edge
Ant queens prefer bison patties when establishing new colonies
Northern flickers often create nest cavities close to the
forest edge.
A large part of the diet of northern flickers are ground
insects.
In particular, they search for and consume a large quantity of
ants, along the forest edge.
The Northern Flying Squirrel
(Glaucomy sabrinus)
Flying squirrels use
abandoned northern flicker
cavities
These squirrels use; “refugia
nests” – for shelter or resting
“Natal nests” for rearing their
young
“Toilet nests” in abandoned
woodpecker holes.
These holes are used
exclusively for defecation
The dung beetle, Aphodius
badiceps only lives on flying
squirrel dung
Aphodius badiceps
Questions
?