Population Demographics and Dynamics of Colonizing Elk in a Desert Grassland–Scrubland

Abstract

Abstract Elk Cervus elaphus are rare in Southwestern desert grassland and desert-scrub habitats, and these habitats are anecdotally considered unsuitable for elk. We studied a colonizing herd in a Southwestern desert grassland–scrubland in northwestern New Mexico to determine the condition and population dynamics of elk in this habitat type. We radiotracked ≤ 24 adult (1.5 y and older) cows and ≤ 8 calves annually, 2003–2006; the sample of radiocollared cows in this study was very close to a census of the entire population for 2004–2006 based on repeated surveys and monitoring. Mean body fat of lactating cows in autumn was 10.6–13.2% in 2003–2004, indicating that lactating elk were acquiring high moderate–low good nutrition, but dropped to 5.6% in 2005 and 6.8% in 2006, indicating poor nutrition for these years of low precipitation. We found adult female survival of 0.94–1.00 and calf survival of 0.38–1.00. Calf survival was related to maternal size, maternal condition, and cumulative annual precipitation through parturition; all calf mortality occurred at or near parturition. Pregnancy rates averaged 0.33 for yearling cows and 0.86 for ≥ 2.5-y-olds, 2003–2006, and pregnancy was positively related to body mass for ≥ 2.5-y-old adults. Lactation rates of ≥ 2.5-y-olds averaged 0.59, 2003–2005, but dropped to 0.30 in 2006, due to poor maternal condition and low precipitation. Since colonization, elk have increased from about 20 to ≥ 53 individuals, a mean rate of increase of 18%/y prior to 2006, but decreasing to ≤ 4% in 2006. The high sustained rate of increase (with few exceptions) indicates that desert grassland–scrubland habitats are suitable for elk and merit consideration in elk management plans of Southwestern agencies.