Brood Break-up, Dispersal, Mobility, and Mortality of Juvenile Prairie Chickens

During a 7-year study of greater prairie chickens (Tympanuchus cupido pinnatus) in Kansas, 24 juveniles were captured, banded, and fitted with radio transmitters. Their monthly ranges and day-today movements showed that they moved more than adults during late autumn and during the spring booming season. They also suffered heavier morta ity than adults, especially during the fall dispersal. Broods broke up before dispersing, and both activities occurred in late August through September. Mortality was about 56 percent for broods under 10 weeks of age, and less thereafter. J. WILDL. MANAGE. 41(1):27-34 Although biologists investigated brood activities of some grouse species in North America, few data are available for greater prairie chickens. Earlier studies of prairie chickens in Kansas (Robel et al. 1970) detected extensive movements of juveniles in October and November. If the increased movements represented dispersal, and the observed high mortality of these dispersing juveniles was representative of all juveniles, then dispersal and resulting mortality might be a force regulating the population. The primary objective of this study was to gather additional information on mobility, mortality, brood break-up, and dispersal of juvenile greater prairie chickens. We wish to acknowledge the cooperation of J. Simpson, owner of the land on which this study was conducted, and the field assistance of J. Tatschl, A. Bisset, and D. Bowen. MATERIALS AND METHODS The study was done in Geary and Waubaunsee counties, 20 to 30 km southsoutheast of Manhattan, Kansas, in 1964-70. The area is typical of the western edge of Kansas Flint Hills bluestem prairie, which extends from Nebraska southward to Oklahoma. The topography and vegetation of the study area were described by Robel et al. (1970). Year-round grazing by cows with calves was light to moderate with some season-long grazing by steers and rotation of pasture use. Some of the pastureland was mowed annually for prairie hay. Juvenile prairie chickens were livetrapped on booming grounds in spring and fall with cannon nets (Silvy and Robel 1967) and throughout the year with funnel-type, walkin traps of various sizes (Watt 1969:34). All caught were banded, and some were equipped with miniature radio transmitters (Marshall and Kupa 1963, Brander 1968) and released. Their subsequent movements were monitored with portable receivers. When a bird with a transmitter moved beyond the range of ground-based portable receivers (0.8 to 1.5 km), portable receivers in a Cessna 120 aircraft were used. At an altitude of 300 m, signals could be received from 13 km. When a bird could not be located after 2 days of ground and aerial searches, its transmitter was assumed to have stopped working. Attempts were made to locate each transmitter-equipped prairie chicken two or three 1 Contribution No. 1266, Division of Biology, Kansas Agricultural Experiment Station, Kansas State University, Manhattan 66506. The study was financed by the National Institutes of Health, the National Science Foundation, and the Kansas Agricultural Experiment Station. 2 Present address: Bays Mountain Park, RR #4, Kingsport, Tennessee 37660. J. Wildl. Manage. 41(1):1977 27 This content downloaded from 207.46. 13.51 on Tue, 21 Jun 2016 06:08:45 UTC All use subject to http://about.jstor. org/terms 28 DISPERSAL OF YOUNG PRAIRIE CHICKENS " Bowman and Robel times a day at different times each day to determine daily and seasonal movements. Occasional continuous monitoring for 10to 24-hour periods supplemented the data on daily movements. Radio-determined locations were plotted on base maps and the outermost points connected to determine monthly ranges for each bird (Mohr 1947). The distances between successive daily locations gave an index of mobility. On any day when two or more locations were recorded for an individual bird, we chose one of them at random to represent that day. Ranges and distances for each juvenile were calculated for each month, movements from the last day of one month to first of the next being recorded in the earlier month. Standard errors were calculated (Snedecor and Cochran 1967:50) for both ranges and distance for each month class. The distance between capture site and the last location was the "effective distance of dispersal" (Johnston 1961).