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.

Successful production of calves is necessary for growth of North American elk (Cervus elaphus Linnaeus 1758) populations, but few studies have evaluated age-related effects on both the conception and survival of a calf to weaning in multiple free-ranging populations. Conception and survival of calves to weaning were both affected by maternal age, with old (age 9 and older) females showing reproductive senescence as compared to prime-aged (ages 2–8) females despite achieving similar or greater size and condition. Reproductive senescence in our free-ranging populations ultimately resulted in old females weaning fewer calves (0.42 calves/female) than did prime-aged females (0.64 calves/female). Other factors, especially maternal size, also influenced conception and survival to weaning, and these interacted with age in a consistent manner, i.e. larger females or females in better condition were more likely to conceive and successfully wean calves within each age class. Female age structure receives less consideration in ungulate management than does male age structure, despite demonstrated impacts on population productivity of multiple species because of reproductive senescence. Because of the large proportion of individuals in senesced age classes in elk populations, low productivity in populations may simply reflect female age structure, rather than other frequently hypothesized factors.

Lactation can have significant costs to individual and population-level productivity because of the high energetic demands it places on dams. Because the difference in condition between lactating and dry Rocky Mountain elk (Cervus elaphus nelsoni) cows tends to disappear as nutritional quality rises, the magnitude of that difference could be used to relate condition to habitat quality or the capability of habitats to support elk. We therefore compared nutritional condition of $ 2.5-yr-old lactating and dry cows from six free-ranging Rocky Mountain elk populations throughout the United States. Our goal was to quantify differential accrual of body fat (BF) reserves to determine whether the condition of dry and lactating cows could be used to define relevant management thresholds of habitat quality (i.e., relative carrying capacity) and consequently potential performance of elk populations. Levels of BF that lactating cows were able to accrue in autumn and the proportional difference in BF between dry and lactating cows in autumn were related (F 1-2,10 $ 16.2, P , 0.001). Models indicated that elk experienced no negative effects of reproduction on condition when lactating cows were able to accrue $ 13.7% BF in autumn. When lactating cows are accruing # 7.9% BF, elk are in a nutritionally stressed condition, which may be limiting population performance. Using the logistic model to predict relative proximity to ecological carrying capacity (ECC), our population-years ranged from 3-97% of ECC and proportion of the population lactating (an index of calf survival) was negatively related to proportion of ECC. Results indicate that the proportional difference in accrual of BF between lactating and dry cows can provide a sensitive index to where elk populations reside relative to the quality of their range. Resumen La lactación tiene un costo significativo en la productividad, tanto a nivel individual como a nivel de la población, debido a la alta demanda energética que se impone en las hembras. Debido a que la diferencia en la condición corporal entre las hembras alce lactantes y secas (Cervus elaphus nelsoni) tiende a desaparecer conforme la calidad nutricional aumenta, la magnitud de esta diferencias podría utilizarse para relacionar la condición con la calidad del hábitat o la habilidad del hábitat para el sostenimiento de los alces. Por lo tanto, comparamos la condición nutricional de hembras lactantes mayores de 2.5 añ os en seis poblaciones de alces pastoreando en las montañ as rocallosas en los Estados Unidos. Nuestra meta era cuantificar las diferencias de las reservas de la grasa corporal (BF) para determinar ya sea que la condición de las hembras lactantes o secas podrían ser usadas para definir un punto de partida apropiado para el manejo de la calidad del hábitat (ej. Relacionado con la capacidad de carga) y por lo tanto la posibilidad potencial del rendimiento de la población de alces. Los niveles de la grasa corporal que fue posible acumular en las hembras durante el otoñ o y la diferencia proporcional en la ...

Uncertainty exists as to which factors are most closely related to probability of pregnancy in Elk (Cervus elaphus), which thresholds are key for managers who want to assess the potential productivity of free-ranging Elk herds, and whether these thresholds vary among populations. We examined relationships among pregnancy, age, and mass for 513 harvested freeranging Elk in Michigan, and compared relationships with other published models and with thresholds derived from other free-ranging and penned populations to see if relationships were consistent among populations. Pregnancy rates varied (χ 2 2 = 136.3; P < 0.0001) among yearling (0.30), prime-aged (2.5-11.5-year-olds; 0.88), and old (> 12.5-year-olds; 0.60) cows. Probability of pregnancy in adult cows was related to mass (χ 2 = 7.4; P = 0.006), age (χ 2 = 12.6; P = 0.0004) and age class (χ 2 = 16.4; P < 0.0001), but not to lactation status (χ 2 = 0.4; P = 0.515); pregnancy was also positively related (χ 2 = 15.8; P < 0.0001) to mass in yearlings. Probability of pregnancy increased 1.02× and 1.04× for each 1 kg increase in body mass of adult and yearling cows, respectively, and prime-aged cows were 4.9× more likely to conceive than old cows. Compared to thresholds derived primarily from penned or farmed Elk, both adult and yearling free-ranging Elk in Michigan and elsewhere were able to achieve higher levels of pregnancy at lower body mass. Thresholds also varied among free-ranging Elk populations. Given variation among populations, managers should calibrate mass-pregnancy relationships for their respective populations to determine whether condition is potentially limiting pregnancy in their populations.

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