Elk Calf Survival and Mortality Following Wolf Restoration to Yellowstone National Park

Abstract

We conducted a 3-year study (May 2003-Apr 2006 of mortality of northern Yellowstone elk (Cervus elaphus) calves to determine the cause for the recruitment decline (i.e., 33 calves to 13 calves/100 adult F) following the restoration of wolves (Canis lupus). We captured, fit with radiotransmitters, and evaluated blood characteristics and disease antibody seroprevalence in 151 calves 6 days old (68M:83F). Concentrations (x, SE) of potential condition indicators were as follows: thyroxine (T4; 13.8 lg/dL, 0.43), serum urea nitrogen (SUN; 17.4 mg/dL, 0.57), c-glutamyltransferase (GGT; 66.4 IU/L, 4.36), gamma globulins (GG; 1.5 g/dL, 0.07), and insulin-like growth factor-1 (IGF-1; 253.6 ng/mL, 9.59). Seroprevalences were as follows: brucellosis (Brucella abortus; 3%), bovine-respiratory syncytial virus (3%), bovine-viral-diarrhea virus type 1 (25%), infectious-bovine rhinotracheitis (58%), and bovine parainfluenza-3 (32%). Serum urea nitrogen, GGT, GG, and IGF-1 varied with year; T4, SUN, and GG varied with age (P 0.01); and SUN varied by capture area (P ¼ 0.02). Annual survival was 0.22 (SE¼0.035, n¼149) and varied by calving area but not year. Neonates captured in the Stephens Creek/Mammoth area of Yellowstone National Park, USA, had annual survival rates .33 higher (0.54) than those captured in the Lamar Valley area (0.17), likely due to the higher predator density in Lamar Valley. Summer survival (20 weeks after radiotagging) was 0.29 (SE ¼ 0.05, n ¼ 116), and calving area, absolute deviation from median birth date, and GG were important predictors of summer survival. Survival during winter (Nov-Apr) was 0.90 (SE ¼ 0.05, n ¼ 42), and it did not vary by calving area or year. Sixty-nine percent (n ¼ 104) of calves died within the first year of life, 24% (n ¼ 36) survived their first year, and 7% (n ¼ 11) had unknown fates. Grizzly bears (Ursus arctos) and black bears (Ursus americanus) accounted for 58-60% (n ¼ 60-62) of deaths, and wolves accounted for 14-17% (n ¼ 15-18). Summer predation (95% of summer deaths) increased, and winter malnutrition (0% of winter deaths) decreased, compared with a similar study during 1987-1990 (72% and 58%, respectively). Physiological factors (e.g., low levels of GG) may predispose calves to predation. Also, the increase in bear numbers since wolf restoration and spatial components finer than the northern range should be considered when trying to determine the causes of the northern Yellowstone elk decline. This is the first study to document the predation impacts from reintroduced wolves on elk calf mortality in an ecosystem already containing established populations of 4 other major predators (i. para determinar las causas del descenso del reclutamiento (de 33 a 13 crías /100 hembras adultas) tras la restauración del lobo (Canis lupus). Hemos capturado, marcado con radiotransmisores y evaluado las características de la sangre y la seroprevalencia de los anticuerpos a enfermedades de 151 crías 6 días (68M:83H). Las concentraciones (x, SE) de los indicadores del estado pote...

Wolves, people, and brown bears influence the expansion of the recolonizing wolf population in Scandinavia

“…v www.esajournals.org calves (Barber-Meyer et al 2008). However, bear predatory efficiency is limited in time, only until the calves are 4 weeks old (Rauset et al 2012), and bears mainly access larger moose by scavenging other predators' kills (Swenson et al 2007).…”

Status and Ecological Effects of the World’s Largest Carnivores

“…In North America, both black (U. americanus) and brown (U. arctos) bears commonly prey on neonatal cervids, taking a large percentage of the annual offspring that are less than 1 month old, and these effects could be additive. In Yellowstone National Park, bears killed more elk (Cervus elaphus) calves than did gray wolves, coyotes (Canis latrans), and pumas combined (43). In Europe, roe deer densities were significantly lower in areas with sympatric wolves and lynx than in areas with wolves alone or areas where both predators were absent (24,34).…”

“…Because of differences in their ecology and human tolerance, pumas are able to persist in areas with much higher levels of human land use than are gray wolves, even though these two carnivores are of similar size. Such differential predator species loss in the face of landscape changes may be especially critical if synergism among multiple large carnivores within predator guilds is required to maintain control over prey populations (34,43). These and other carnivore species make kills in different habitats, or scavenge to supplement their diets, which can determine the nature and rates of prey kills and consumption (53, 69).…”

Behaviour of brown bears killing wild ungulates in the Cantabrian Mountains, Southwestern Europe

“…These figures suggest that the impact of bear predation on the ungulate population is probably very small. However, in order to be sure, ungulate mortality would have to be studied, requiring fawns to be tagged (Barber-Meyer et al 2008;Swenson et al 2007). …”

“…Bears may also kill adult ungulates, but mainly concentrate on calves in the first 4 weeks after birth in spring and early summer (Barber-Meyer et al 2008;Zager and Beecham 2006). In a review of black (Ursus americanus) and brown bear predation on ungulates in North America, Zager and Beecham (2006) suggested that predation is additive at low ungulate densities and can become compensatory as prey density approaches carrying capacity.…”