Expected Impacts on Greater Prairie-Chickens of Establishing a Wind Turbine Facility Near Rosalia, Kansas, Part Three

Greater prairie-chicken population trends in Butler County
For survey purposes, the greater prairie-chicken range in Kansas is divided into four physiographic regions (Figure 2). The Flint Hills region extends from Riley county on the north, southward through the Flint Hills to the Oklahoma border. The Flint Hills region includes Butler County plus eight other counties, and is bordered on the east by the Eastern Cropland region, on the southeast by the Blackjack region, and on the west by the Western Cropland region.

Figure 2. Prairie-chicken survey regions in Kansas. No. 1 in southwestern Kansas is the primary range of the lesser prairie-chicken; whereas, Nos. 2 through 5 include the primary range of the greater prairie-chicken in eastern Kansas. Map reproduced from Church 1987 (Unpubl. Unit Report: 1987 prairie-chicken lek-count survey).
 

Since 1980, with few exceptions, the lek-survey indices of greater prairie-chicken populations have been higher in the Flint Hills region than in the other survey regions in Kansas. The Butler County lek-survey route is located approximately 20 miles northwest of Rosalia, adjacent to Chase County. Lek surveys have been conducted on the Butler County route since 1963 and the greater prairie-chicken population indices determined from that route have been the highest or second highest of the indices each year in the Flint Hills region since the survey’s inception (Kansas Department of Wildlife and Parks, unpubl. reports). Below is a comparison between the greater prairie-chicken population indices for Butler County and those for all of the Flint Hills region over the last 22 years.

	Lek-survey index (birds per square mile)
Time period	Flint Hills region	Butler County
1980-84	11.0	19.1
1985-89	9.9	14.2
1990-94	8.4	14.5
1995-99	6.0	11.6
2000-02	6.7	15.2

If the lek-count-survey indices reflect gross population numbers, the preceding data indicate that the area along the Butler County lek-survey route has a greater prairie-chicken population exceeded by few other locations in the Flint Hills region.

Factors associated with greater prairie-chicken population trends
Greater prairie-chickens are birds of the open grassland prairies and are intolerant of human intrusions into their environment. The conversion of grasslands to intensive row-crop agriculture has had the most detrimental impact on greater prairie-chicken populations across their historical range (Schroeder and Robb 1993, Svedarsky et al. 2000).

When row-crop agriculture began in Kansas, it had a positive influence on greater prairie-chicken populations because the small grains supplemented the natural food sources of the birds, especially during severe winter months (Applegate and Horak 1999). The long-term decline in the greater prairie-chicken population of Kansas began in the late 1800s and was coincidental with more grassland being converted to intensive agriculture. The loss of grassland habitat plus the drought years of the 1930s and 1950s drastically reduced the numbers and range of the greater prairie-chicken in Kansas. Since the 1950s, the loss of grasslands slowed in Kansas and the greater prairie-chicken gradually increased its range and numbers (Applegate and Horak 1999). The soils of the Flint Hills of Kansas are shallow and underlain by layers of limestone. Thus, the tallgrass prairies of the Flint Hills were not readily converted to row-crop agriculture and became the stronghold of the greater prairie-chicken population in Kansas.

During the 1960s and 1970s, the population of greater prairie-chickens in Kansas fluctuated with annual changes in weather conditions, primarily weather conditions during the nesting and brood-rearing seasons. The Kansas indices to greater prairie-chicken populations reflected relatively stable populations through the 1980s, but since have indicated a declining population. The trend is quite obvious for the statewide index, but appears in the index to the greater prairie-chicken population in the Flint Hills region as well. There has not been an obvious increase in conversion of grassland to row-crop agriculture in eastern Kansas during the 1990s (Cartwright 2000). If the lek-survey indices truly reflect greater prairie-chicken population trends, the cause for the declining population since the 1980s must be associated with something besides loss of native grassland to agricultural activity. Several Kansas Department of Wildlife and Parks’ biologists (Rodgers, personal comm., Applegate and Horak 1999) have speculated that changes in the management of the grasslands by livestock producers have been implicated in the decline of the greater prairie-chicken population in Kansas.

Grasslands in Kansas commonly are grazed by livestock and therefore the grasslands generally are referred to as rangelands by their owners. The management of rangelands in eastern Kansas is accomplished primarily by a combination of grazing and burning, with some brush control done with chemical applications. Range management is a complex discipline combining science with common sense. A successful range manager must interact continuously with a constantly changing rangeland ecosystem, while responding to current and future economic constraints and opportunities (Robel 2001).

Range managers strive to manipulate rangeland vegetation in such a way that it maximizes the sustained yield of grazing animals. Because domestic animals generally are the grazers with the highest economic value, range managers concentrate on maximizing the production of cattle, sheep, goats, and other commercial livestock. Wildlife populations on most managed rangelands, including greater prairie-chickens of Kansas, are incidental byproducts of livestock management.

Extensive research has been conducted by range scientists to determine the “proper utilization” of most rangeland forage species. Proper utilization is the maximum point of defoliation that continues to maintain desirable range productivity (Heady and Child 1994). Proper utilization of most rangeland vegetation results in average stubble grass heights ranging from 1 to 4 inches (for Buchloe dactyloide and Agropyron smithii, respectively). Heavy stocking rates reduce the average stubble height and light stocking rates result in taller stubble heights. Generally these stubble heights are shorter than optimal for greater prairie-chickens.

Vegetation heights of good nesting habitat for greater prairie-chickens range from 8 to 11 inches in Kansas (Horak 1985) and 10 to 28 inches in Oklahoma (Jones 1963). Similar heights of vegetation cover are needed for good brood range, day and night roosting, and winter cover.
Many progressive ranchers in Kansas attempt to graze their rangelands at “proper utilization” levels which often results in standing vegetation shorter than is optimal for greater prairie-chicken nest success and brood survival. Different livestock grazing systems (intensive-early, season-long, late-season, plus others) produce vegetative stands of different plant composition and structure. Increases in the proportions of ranchers adopting proper utilization stocking rates and shifting from season-long to intensive-early grazing systems appear to be associated with declines of greater prairie-chickens in the Flint Hills of Kansas. However, no research has been conducted to determine if a cause-effect relationship exists between stocking rates and grazing systems and the population trends of the greater prairie-chicken in Kansas.

In eastern Kansas, periodic fire is necessary to maintain tallgrass prairie (Hulbert 1988). Without fire, these grasslands are invaded by woody species (Owensby 1994). Prescribed burns in the spring every 3 to 5 years following 2 or 3 years of successive burning are sufficient to control the invasion by woody species. These burns also increase the nutrient quality of rangeland vegetation for livestock (Owensby 1994), thereby elevating livestock gain rates by 10 to 15%. This increased livestock production has encouraged annual burning of the Flint Hills, and more frequent burning has detrimental impacts on nesting by grassland birds (Robel et al. 1998). Costs of burning decreases with increasing size (at least up to 1250 acres), therefore burning large tracts of land has become a common range-management strategy in the Flint Hills. The increased frequency and expanse of spring burning of rangelands in eastern Kansas are thought to be involved in declines of greater prairie-chicken populations in Kansas (Rodgers, personal comm., Applegate and Horak 1999). Again, however, no large-scale controlled research has been conducted to determine if a cause-effect relationship exists between burning frequency and expanse on the declines of greater prairie-chicken populations in the Flint Hills of Kansas.

Although herbicides are sometimes used to reduce woody species, poisonous plants, cropland weeds, and herbaceous plants competing with grasses in the grasslands of Kansas, their use is very limited. Other management methods (e.g., grazing and burning) are better suited than herbicides for modifying vegetation composition and structure of tallgrass prairie habitats. There are no research data showing a relationship between herbicide use and greater prairie-chicken population trends in Kansas.

In summary, there are no research data associating any specific factor with the decline of greater prairie-chicken populations in Kansas. Speculation and circumstantial evidence points to changes in grazing systems and frequency of rangeland burning as possible causes of the recent declines, but no large-scale research has been done to document such. Other possible explanations include changes in predator populations, increased human activities, encroachment of woody vegetation into the grasslands, climatic changes, and hunting pressure. Although each possibility is intriguing, there are few experimental data to relate these latter possible explanations to the statewide decline of the greater prairie-chicken in Kansas.

Continue to Part Four