Crater Lake National Park: Ecology Of Elk Inhabiting Crater Lake National Park And Vicinity
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Study Area


Results and Discussion

Management Implications

Literature Cited

Appendix A


Capturing and Collaring

Elk were trapped primarily during May 1985 in five portable corral traps (Harper 1985) located in the Winema National Forest just south of the park boundary. Traps were prebaited with salt and mineral blocks during fall 1984 and 1985, and baits persisted through trapping periods each of the following springs. Trapped elk were immobilized using powdered succinylcholine chloride administered using a CO2 powered Cap-chur (TM) rifle and reloadable Pneu-darts. Immobilized cow elk were fitted with color-coded Telonics radio-transmitter collars that transmitted in the 151 mHz range. Sub-adult bulls and cows were marked with numbered eartags and vinyl ear streamers.

Radio-tracking Procedures

Radio-collared elk were relocated for 18 months between May 1985 to October 1986. Three seasonal periods were recognized for data collection and analysis, including:

spring:15 May - 15 June, 1985, 1 April - 15 June 1986
summer:15 June - 15 October 1985, 1986
winter:1 November - 15 April 1985-86

Seasonal periods correspond to approximate dates of arrival of radio-collared elk on discrete spring, summer, and winter ranges, respectively.

Due to seasonal differences in the accessibility of the study animals, a variety of telemetry sampling schedules and techniques were employed throughout the seasons. During spring, elk were easily monitored from extensive road networks. Elk were relocated one to three times daily during early morning, midday, and late-night sampling periods. To obtain each relocation, bearings were taken from two to six telemetry stations along roads until the elk's location could be established by plotting bearings on a gridded map of the study area. To minimize telemetry errors, telemetry stations were chosen as close as possible to the elk's location, and such that angles of intersecting bearings averaged between 60° - 120°. If bearings did not intersect, if elk were further than 1 km from a road, or if accuracy of the location was doubtful, telemetry equipment was used to approach the elk and verify its location. Coordinates of such points were recorded using a Universal Transverse Mercator (UTM) grid system, for subsequent assignments of vegetation classes of elk locations.

During winter, summer, and intervening migration periods, an attempt was made to adhere to the same sampling schedule used during spring. However, elk frequently inhabited remote roadless areas or areas that were inaccessible because of deep snow, preventing a systematic sampling regime. During such times, elk were relocated at least once a week from fixed-wing aircraft equipped with strut-mounted yagi antennae. Attempts were also made to approach each collared elk on the ground each week, either on foot, horseback, or off-road vehicle. A total of 1-7 relocations of radio-collared elk were thus obtained each week depending on season and ease of access.

Population Characteristics

Efforts to monitor herd numbers and composition were concentrated on spring range in the Upper Klamath Basin, where elk could be observed grazing in pastures without disturbing them. During April - May 1985, prior to calving season, elk were counted each morning between 0530 and 0700 by driving a fixed route along pasture perimeters. The survey route originated at the USFS Seven Mile Guard Station, proceeded east on Seven Mile Road to Highway 62 and northwest on highway 62 to USFS Road 3227. All observed elk were classed as calves (<1 year old), adult females (>1 year old), yearling males (spike antlers) or adult males (branched-antlered males). No special efforts were made to obtain visual contacts with elk during the remainder of the year, because dense vegetation generally obscured portions of the herds, and because it was felt that associated disturbance factors would bias habitat use patterns. Nonetheless, all incidentally observed elk were classified throughout the study, which yielded some supplemental information on population characteristics.

Seasonal Movements and Home Range

Home range is the area used by an animal to obtain necessary nutrients. shelter and security requirements, as well as potential mates and areas for reproduction. These resources are obtained either within a single annual home range or, as was the case in this study, among several sequentially used seasonal home ranges connected by migratory pathways.

Home ranges of radio-collared elk were delimited for each seasonal period using the harmonic mean method (Dixon and Chapman 1980). The harmonic mean home range method generates contour intervals that encompass specified percentages of the spatial distribution patterns of animals. For this analysis, seasonal home ranges were based on contours that encompassed 80% of the probability distribution of all elk locations. Home ranges were based on composited locations of all radio-collared elk to provide an overview of the population distribution patterns. All maps of elk home ranges were generated using MCPAAL software for IBM-compatible microcomputers (Stuwe and Blohowiak, undated).

Habitat Use Patterns

Elk habitat use was evaluated by season to determine vegetation characteristics that were used by radio-collared elk significantly more (i.e., preference) or less (i.e., avoidance) than random use. The analyses of vegetation types used by elk varied among the three seasonal ranges, reflecting differences in vegetation maps available for the areas. On the summer ranges within CRLA, vegetation had been classified and mapped according to dominant overstory tree species (Walsh 1977). On spring ranges of the Winema National Forest, stands were mapped according to dominant overstory species, stand size-classes, and densities. On winter ranges of the Rogue River National Forest, vegetation had been mapped according to designated elk habitat components and tree size-classes. Elk habitat components on winter range included foraging areas (<60% shrub or tree overstory closure), hiding cover (vegetation capable of hiding 90% of a standing elk at 200 feet), thermal cover (overstory >40 feet tall and >70 feet enclosure), and optimal cover (dominant trees >21" dbh and >70% crown closure. Additional descriptions of elk habitat components are provided by Witmer et al. (1985).

Vegetation preferences (or avoidance) were determined by comparing use by elk of each of those vegetation classes to their availability within the seasonal composite home range. Seasonal use was determined as the proportion of pooled telemetry locations that fell within a vegetation class. Availability was determined as the proportion of a composite home range area occupied by each vegetation class. Land areas used to estimate availabilities of vegetation classes were measured directly from vegetation maps using a digital planimeter. Use of vegetation classes by elk that was significantly greater or less than availability was detected using Bonferroni z-tests for equality of proportions (Neu et al. 1974). Experiment-wise error rates for multiple comparisons were controlled at p <10.

Last Updated: 11-Aug-2016