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Integrated Management of the Greater Prairie Chicken and Livestock on the Sheyenne National Grassland

Predation


Prairie chickens have evolved with a variety of predators and have developed various predator defense/avoidance strategies. Fortunately, there are no exotic predators, other than domestic dogs and cats, which they have to contend with in the Northern Great Plains. They have expanded north of their original range however, and are exposed to goshawks, for example, which they ordinarily would have had limited exposure to since the goshawk is a bird of the Northern forest. They can be a very effective predator of prairie chickens, especially displaying birds in late winter or early spring. This vulnerability is possibly attributed to lack of evolutionary exposure to goshawks (Fred Hamerstrom, personal commun.).

Although prairie chickens have evolved with a variety of predators, man has modified the landscape in various ways so that vulnerability may have changed as well as numbers of certain predators. For example, large cottonwood trees along prairie ditches and electrical poles have provided perching sites from which raptors can hunt. The presence of rock piles, bull-dozed piles of brush, and abandoned buildings has provided denning sites for mammals such as raccoons and striped skunks.

Greater predation in spring?

In Missouri, Burger (1988) found 38 of 63 mortalities to be due to raptors, particularly great horned owls and red-tailed hawks. He found that females seemed most susceptible to predation during the nesting period; of added consequence because both the hen and her potential production are lost. Newell (1987) also noted most mortality at SNG was in May and believed it may have been related to the raptor migration.

Burger (1988) also found annual survival related to movements. Birds with less than the seasonal mean of movements survived twice as long as those moving more than the seasonal mean. Moving a lot not only expends energy but places birds in unfamiliar surroundings which reduces the efficiency of food location and probably predator detection as well. Burger found that females living in a diverse, mosaic of habitat types moved more than those associated with a larger block of prairie and had lower survival.

Spring may be a period of higher mortality for male prairie chickens as well due to greater exposure (and perhaps reduced alertness) on booming grounds and the high numbers of migratory raptors moving through. Toepfer (1988) believed that kills on booming grounds are uncommon but they do occur. He summarized published reports of booming ground kills and noted the following: goshawk - 10, cooper's hawk - 2, red-tailed hawk - 1, great horned owl - 1, and snowy owl 1. Svedarsky had an additional observation of a goshawk kill on a booming ground in northwest Minnesota and Burger (1988) had evidence of 3 red-tailed hawk kills on booming grounds. All the raptors noted above are "perch hunters", and tree removal in prairie chicken habitat is a recommended practice in some areas (Burger 1988) to reduce hunting perches. Tree removal would also reduce nesting sites for great horned owls and red-tailed hawks; ordinarily not common raptors in the open prairie (Robert Murphy, personal commun.). Nesting sites for crows and magpies (nest predators in some areas) would also be reduced by tree removal.

Great horned owls are perhaps one of the most significant avian predators of prairie chickens since they are effective predators where there are perches, and are year-around residents. Snowy owls, while efficient predators, are only sporadically present in the winter and early spring; usually leaving to the North with snow melt.

Mammalian predators

Red fox and skunks are probably the most common mammalian predators of waterfowl and prairie grouse nests in the Northern Great Plains. Foxes have more impact than skunks because they commonly prey on the nesting hen as well. Over a third of nest failures in Missouri were due to predation of the female (Burger 1988). From 1974 to 1984, Svedarsky (1988) found December fox fur prices to be positively correlated (r = 0.82, P<0.01) with spring booming ground counts, 2 springs later. The assumption was that trapping effort goes up with the market incentive and that other potential predators are trapped as well (skunks, feral cats). If trapping (and hunting) did, in fact, reduce mammalian predator numbers, it should result in higher prairie chicken production the next year and higher booming ground counts the following year. This appeared to be the case.

Further evidence for the high impact of foxes on larger ground nesting birds is that coyotes tend to displace foxes when they occur together and nest success usually increases as a result. Sovada et al. (1995) studied comparable areas in the Dakotas except that some were dominated by red foxes and others by coyotes. Nests in coyote areas experienced nearly twice (32%) the nesting success as in fox-dominated areas (17%). They suggested favoring coyotes in an area could be an effective method of increasing duck nest success. Svedarsky (unpublished data) observed an increase in nest success from 1990 to 1991 of 8.3% to 61.3% in a Minnesota study area as coyotes apparently displaced foxes.

Management considerations

There are a variety of predators at the SNG (Table 6) which could affect prairie chickens. They may vary on a seasonal basis, some a threat to adults only (winter), others prey on eggs only (e.g., Franklin's ground squirrel), and others eggs or chicks and adults. Specific predator control is often not practical because of the cost and intensity required but there are management approaches to reduce predation; some of which have been discussed under other sections. The following have been suggested in the literature to increase nesting success: improve cover characteristics of nesting cover, reduce predator access trails in nesting cover, and reduce predator denning/nesting sites and hunting perches to safeguard nesting hens. Also, there is evidence that by increasing the block size of cover areas, nesting success is likely improved (Ball et al. 1995). Ball et al. (1995) studied duck nesting in a heavily grazed area of Montana and recorded at least 48 broods/100 breeding pairs with variation in productivity attributed to block size and red fox vs. coyotes domination. Burger (1988:100) recommended for Missouri, "Management of greater acreages of nesting cover in larger tracts may reduce prairie chicken nesting density and predator efficiency, thereby increasing nest success and female survival."

Block size at the SNG is intermediate in size between Minnesota habitats and Montana because of pasture sizes. Raptor perching trees could be reduced however and thereby reduced hunting efficiency of at least a portion of the predator population.

In the mid-1960's the SNG was apparently fox-dominated and has shifted to a coyote-dominated system at present (Harold Simpson, personal commun.). If so, this factor in itself could be responsible for enhanced productivity of prairie grouse at the SNG in spite of reduced levels of residual vegetation.


Table 6. Likely predators of prairie chickens and/or their nests at the Sheyenne National Grassland.

Season of Impact
Species Winter Spring Summer Fall
Great horned owl x x x x
Snowy owl x      
Red-tailed hawk   x x x
Swainson's hawk   x x x
Marsh hawk   x x x
Cooper's hawk   x x x
Coyote x x x x
Red fox x x x x
Domestic dog   x x x
Badger   x x x
Raccoon   x x x
Striped skunk   x x x
Domestic cat     x  
Mink   x    
Long-tailed weasel   x    
Franklin's ground squirrel   x    


Summary

  1. Prairie chickens have evolved predator defense strategies against a variety of predators but land use changes have affected their vulnerability to certain predators and increased the numbers of others.

  2. The reproductive season (late winter - early spring) is probably the period of greatest predation of females, their chicks, and males due to movements associated with breeding, nesting, and brood rearing. Contributing factors from predators include increased prey demands due to their reproductive activities and increased number of migrating raptors.

  3. Nesting success is usually higher in a coyote-dominated landscape as opposed to a fox-dominated one.

  4. Management to increase nesting success could include:
    1. maintenance of optimum residual covers for nesting, breeding, and roosting.
    2. reduction of predator access trails in cover.
    3. reduction of nesting/denning sites for predators.
    4. reduction of raptor hunting perches.
    5. increase the block size of nesting cover.
    6. maintenance of a coyote-dominated landscape.

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