Movements, habitat use, and population dynamics of elk in Guadalupe Mountains National Park, Texas

Abstract

The elk (Cervus elaphus) population in and adjacent to Guadalupe Mountains National Park, Texas was studied to determine its current status and use of habitat, as well as to better understand factors in the population decline observed since the 1960's. Elk were observed from January 1988 to December 1989. Herd characteristics and behaviors were recorded as well as habitat use. Forage quality was assessed through a series of vegetative transects. Hypotheses for the population decline were considered using field data, historical data, and a population model. Field observations indicated the population had continued to decline, to < 30 animals by 1989. Area used by elk also had decreased. Water availability had continued to decline as 2 earthen tanks held water for shorter periods. This had resulted in much-reduced usage of parts of the elk range farthest from permanent water. Two non-interacting groups of elk, designated the Dog Canyon Group and the Frijole Group, were found in the park. Over 83% of dry-season locations of the Dog Canyon Group were < 2 km from water while 72-100% of dry-season sightings of the Frijole Group were <2 km from water. Natality and/or calf survival had improved since 1978. Oaks (Ouercus spp.), mountain mahogany (Cerocarpus montanus, and desert ceanothus (Ceanothus greggii) appeared to be preferred browse species, while junipers (Juniperus spp.) were avoided. Mountain shrub habitat was selected for by both the Dog Canyon and Frijole groups, while desert shrub and pinon-juniper were selected against. Examination of hypotheses for the elk population decline indicated that disease, in utero or postnatal mortality, or loss of genetic heterozygosity were unlikely to have caused the continuing decline. While forage quality may have been involved in the original decline, water loss and predation appeared most likely to be responsible for the long-term decline. The population simulation indicated that predation may have been suppressing the population even through 1989. The long-term forecast is extirpation of the population. Even if calf survival were to increase to an optimal level, the present population is so low that accidental deaths could cause extirpation.