Variation in Defecation Rates of Pronghorns Relative to Habitat and Activity Level

Abstract

During June through September, 1977, pronghorn antelope (Antilocupra americunu) were observed in the National Bison Range, Moiese, Montana, to determine if defecation rates were constant in different habitat types and at different levels of activity. Individuals and groups that were active 50% or more of observation periods were found to have defecation rates approximately 10 times greater than groups or individuals that were active less than 50% of observation periods. Habitat type was much less tightly related to defecation frequency than was activity level. The use of pellet-group counts as indices of ungulate numbers and habitat use was reviewed by Neff (1968). In this review, he stated that deer are assumed to deposit pellet-groups most frequently in areas where they spend the most time. Other authors, including White (1960), Bowden et al. (1969), McCaffery and Creed (1969), Gill et al. (1975), and Kearney and Gilbert (1976) have made the same assumption for deer and other ungulates. If this assumption is not true, the pellet-group count is one of the most economical approaches available to a land manager concerned with assessing wild ungulate use of specific blocks of land. If the assumption is not true, use of this technique could provide biased information that would lead to poor management decisions. This study was designed to gather quantitative information on pronghorn defecation rates in selected habitat types to determine if frequency of defecation were independent of habitat type and activity level of observed animals. observation segments were often truncated because observed animals moved into different habitat types or moved into positions where defecation could not be seen. The activity of observed animals, the number of defecations, the physiognomy of vegetation, and the terrain physiography were recorded for each observation. Habitat types were defined as a combination of growth form of dominant vegetation (grassland, grass-shrubland, treeshrubland), presence or absence of slope, and aspect (cool slopesN, NW, E, NE; warm slopes-W, SW, S, SE). All observations within 10 m of a pronounced change in vegetation or terrain configuration were considered ecotonal and were designated as the habitat type “ecotone.” The National Bison Range, located in the Flathead Valley approximately 50 km north of Missoula, Montana, was selected as a study site because resident pronghorns were easy to observe and were well habituated to moving and standing vehicles. The terrain of this 7,700 ha refuge is characterized by rugged hills in the southern and central sections and rolling plains in the northern sections. Dominant grasses include bluebunch wheatgrass (Agropyron spicatum), Idaho fescue (Festuca idahoensis), and rough fescue (F. scabrella). Bromus spp., Poa spp., and Aristida spp. are common on disturbed sites (Morris and Schwartz 1957). Only the higher hills are forested. Douglas fir (Pseudostuga menziesii) is dominant on northern exposures, and ponderosa pine (Pinusponderosa) is dominant on southern exposures. Common shrubs include snowberry (Symphoricarpus occidentalis) in swales, chokecherry (Prunus demiss), serviceberry (Amelanchier aln$olia), and mockorange (Philadelphus lewisii) on scree and rock outcrops, and ninebark (Physocarpus malvaceus) on the margins of Douglas fir stands (Morris and Schwartz 1957, Kitchen 1974). In order to avoid splintering the sample, activity classes were pooled. “Active” animals were defined as those involved in feeding, moving, or social interactions. “Inactive” animals were defined as those lying or standing. In most observation periods, several individuals were observed together. The total animal-minutes recorded during each period were categorized as “high activity” (50% or more of the animal-minutes recorded as active observations) or “low activity” (less than 50% of the animal-minutes recorded as active observations). Male and female pronghorns were treated as separate sampling strata because of the territorial marking behavior of males (Kitchen 1974). Fawns were included with the female stratum. Data were analyzed using one-celled Chi-square analysis (Steele and Torrie 1960) and analysis of variance in the randomized block design (Steele and Torrie 1960). Results and Discussion During June through September 1977, 600 or more animalminutes were recorded in each of four habitat types utilized by male and female pronghorns (Table 1). This sample was small but was considered minimally adequate for the tests conducted. One-cell Chi-square analysis (Table 2) indicated no significant deviations from expected defecation frequency for any of the habitat types when all animal-minutes were considered. A breakdown of observations into “high activity” and “low activity” subsamples revealed that defecation occurred significantly more often Table 1. Animal-minutes and observed defecation for pronghorns in four habitat types and two activity classes in the National Bison, Range, June-September 1977.