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Prairie chickens spend over half their life on a roost, especially in the North with extended winter nights. Roosting sites must provide a measure of protection from weather but, more importantly, safety from predators. The latter could involve preventing detection from predators and sites which facilitate escape from predators in case of detection. On occasion, Svedarsky has flushed roosting coveys of gray partridge off snow-free gravel roads in the winter when snow covered the remaining landscape. Certainly, an elevated roadway is one of the most climatically exposed sites available, but it was initially thought that their clumped form was a rock and perhaps a great horned owl would as well! Roosting cover is critical year-round, but perhaps more so in the winter when it is closely tied to food resources.

Roost sites should be accessible to adequate winter food resources in order to minimize movements which utilize energy and increase exposure to predators. Burger (1988:88) noted for Missouri: "Our observations suggest that prairie-chickens select optimal winter roosting habitat, then make daily feeding movements radiating as far out from this habitat as necessary to meet energetic demands." This suggests that roosting habitat may be more of a limited resource than food in more snow-free areas. Farther north, food may be more limiting, but still needs to be close to night roosts. For Wisconsin, Schmidt (1936:197) said, "Food determines what range is habitable in winter, but so does cover, particularly roost cover." Hamerstrom et al. (1957) believed winter cover was not limiting since when the herbaceous vegetation got covered with snow, birds used woody cover (fairly abundant in the Wisconsin prairie chicken range). In a photo caption (page 57) they noted, "Here bluegrass is (matted) down, under ten inches of snow, but sedges, quack, timothy and Muhlenbergia still give roosting cover." Later, using radio-tagged birds, Toepfer (1988) found 57.1% of 175 winter roosts in "wetland" habitat in western Wisconsin and 51.8% of 307 locations in "wetland/shrub" habitats in central Wisconsin.

Manske and Barker (1988) identified the following as winter roosting habitats at the SNG based on observations of prairie grouse (sharptails and prairie chickens) roost sites: switchgrass portion of midland community, shelterbelts and other woody vegetation along cropland edges, and snow when it became >30 cm deep in drifts along shelterbelts and the lee side of hummocks. Toepfer and Eng (1988) following 20 radio-tagged prairie chickens at the SNG, found 64.0% of 525 night locations in lowland grass and shrubs, followed by reed canary grass (13.7%), shrubs (11.8%), midland grasses - primarily little bluestem (7.4%), and quackgrass (7.1%). Manske and Barker (1988) recorded no winter night roost sites in the "Lowland Grassland" habitat type.

Predator avoidance strategies?

While lowlands tend to support taller vegetation than more upland areas, there may be advantages in predator avoidance as well. Gratson (1988) suggested that canid predators likely spend comparatively less time hunting small mammals in lowlands thus reducing chances of happening on to roosting prairie grouse. He also suggested that there tend to be fewer trees in wetlands which could serve as hunting perches for great horned owls, an important nocturnal and crepuscular predator. Gratson found the greatest preference for lowland roosting for sharptailed grouse in Wisconsin when birds were snow-burrowing. This would negate any possible thermal advantages of roosting there compared to upland sites assuming that snow was equally available in all sites. Gratson also discussed the possible predator avoidance strategy of birds changing roost sites often since predators may return to sites of previous prey captures. Toepfer and Eng (1988) found the average distance between successive night locations was 922 m (.6 mile), indicating that prairie chickens shift roosting sites.

In northwest Minnesota, Rosenquist and Toepfer (1995) found several habitats used for roosts but areas with forbs, especially alfalfa and goldenrod, appeared to provide the best snow burrowing conditions. CRP lands with brome and alfalfa were used when snow conditions permitted burrowing. Native prairie was used little due to snow packing and willow areas received little direct use but the associated herbaceous vegetation within willow complexes was often used since it tended to accumulate snow providing good burrowing conditions. Birds rarely roosted under willow branches but, on one occasion, a roosting bird was apparently depredated when it flushed up into willow branches from a snow burrow (Eric Rosenquist, personal commun.).

While a snow burrow is ordinarily a good place to roost, it can be disastrous if extreme conditions cause hard crusting. Lindsay (1967) recounted that in the winter of 1932-33 in northern Wisconsin, west of Hurley, a mild day with a misty rain was followed by extreme cold (perhaps down to -40o). The snow crusted over hard enough to support a horse in many areas. Prairie chickens had been common in the area but at once became scarce. Several residents found dead birds under the snow and more after the snow began to melt in the spring. Lindsay (1967:25) believed: "From my own observations, we must have lost the entire prairie chicken population of that area at that time. I haven't seen a chicken in Iron County since."

What constitutes "good" winter roosting cover?

Toepfer and Eng (1988) at the SNG found over 85% of the winter night locations in cover class III and over (>25 cm). VOR's for 32 vegetation roosts averaged 2.1 dm. Manske and Barker (1988) did not separate data for winter roosts but found an average VOR for night roosts throughout the year of 1.9 dm (range: 1.5-2.2 dm). From these data, they concluded, "1.5 dm is the minimum level for good night roost habitat" Manske and Barker (1988:18). If one considered the midpoint of a range or a mean to indicate "good", an alternate view would be to average Toepfer and Eng's average of 2.1 dm for vegetation sites with Manske and Barker's overall average of 1.9 which would yield 2.0 dm as a standard of "good" winter roosting cover. This would not include considerations of snow burrowing but, for monitoring purposes, (McCarthy et al. 1995a) only vegetation characteristics were used.

Roosting cover in the snow-free period

McKee (1995) collected roost data from all seasons in Missouri and found an average VOR of about 20.4 cm (range 10-35) but no pattern of site selection was apparent. In Colorado, Schroeder and Braun (1992:16) indicated that, "Roosting typically occurred in mid and tall vegetation in relatively dense grassland areas in all seasons" but presented no quantitative data.

For Oklahoma, Jones (1963) noted the following vegetation heights used for night roosts by season: winter - 13 cm, spring - 4 cm, summer - 32 cm, and fall - 5 cm. These values are perhaps biased towards shorter cover since Jones was not working with radio-tagged birds and roost forms are more difficult to locate in heavier cover. Toepfer (1988), following radio-tagged prairie chickens in Wisconsin, found vegetation shorter than 25 cm was regularly used during the day but not for night roosting when about 90% of locations were in cover >25 cm. "Grass/Forbs" were a major habitat used in all 4 seasons in central Wisconsin followed by "upland grass" (Table 5). At Crex Meadows, in western Wisconsin, "edge" was a major habitat used, followed by "wetland."

^a Number of locations.

Summary

1. Roosting cover generally refers to cover used at night and prairie chickens generally roost on the ground.
   

2. Roosting cover must provide protection from climatic factors but protection from predators is probably more important. Evolution would favor the selection of roosting cover which reduces detection by predators and facilitates escape should detection occur.
   

3. Roosting cover should be relatively close to food resources, particularly during the winter when movements expend energy and increase exposure to predators.
   

4. In the North, herbaceous forbs and/or some woody vegetation are important elements of good roosting cover if they promote the accumulation of snow adequate for snow burrowing. Predominantly graminoid cover, if low in forbs, may be of limiting winter roosting value.
   

5. Vegetation providing 100% VOR at 2.0 dm is suggested as a better standard of roosting cover than 1.5 dm at the SNG.
   

6. Lowlands are commonly preferred roosting sites in many parts of the prairie chicken range and there is evidence that their selection is related to predator avoidance as well as better concealment in the heavier vegetation which occurs there. This function of lowlands should be emphasized at the SNG.
   

7. There is some evidence that crusted snow can cause mortality of snow roosting prairie chickens.