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Ungulates migrate to maximize nutritional intake when forage varies seasonally. Populations of ungulates often include both migratory and non‐migratory individuals, but the mechanisms driving individual differences in migratory behaviour are not well‐understood.We quantified associations between hypothesized drivers of partial migration and the likelihood of migration for individual ungulates that experienced a range of environmental conditions and anthropogenic influences.We evaluated the effects of forage variation, conspecific density, and human land uses on migratory behaviour of 308 adult female elk in 16 herds across western Montana.We found irrigated agriculture on an individual's winter range reduced migratory behaviour, but individuals were more likely to migrate away from irrigated agricultural areas if better forage was available elsewhere or if they experienced high conspecific density on their winter range. When the forage available during the summer growing season varied predictably between years, elk were more likely to migrate regardless of whether they had access to irrigated agriculture.Our study shows that predictable availability of beneficial native forage can encourage migration even for ungulates with irrigated agriculture on their winter range. Perturbations that can affect the forage available to ungulates include wildfires, timber harvest, livestock grazing and changing weather patterns. If these or other disturbances negatively affect forage on summer ranges of migrants, or if they cause forage to vary unpredictably across space and time, our results suggest migratory behaviour may decline as a result. [ABSTRACT FROM AUTHOR]

During late summer and fall, elk (Cervus canadensis) need access to adequate nutrition to support physiological requirements for reproduction and overwinter survival. The archery hunting season often occurs during this period and can affect distributions of elk as they seek areas that minimize perceived harvest risk. Areas that confer lower harvest risk may provide relatively low‐value nutrition, resulting in a potential tradeoff between minimizing risk and accessing adequate forage. We used radio‐collar data collected from female elk during late summer and fall (Aug–Oct) and estimated resource selection models to evaluate the extent of this potential risk‐nutrition tradeoff. To evaluate if elk exposed to a greater hunting risk altered selection for forage resources, we assessed the relationship between individuals' selection coefficients for forage and the proportion of their late‐summer‐fall home range accessible to hunters (our metric of hunting risk). Our results indicate that during the archery season, elk with higher‐risk home ranges selected more strongly for areas farther from motorized routes than elk with lower‐risk home ranges. Regardless of the level of risk, however, elk maintained or increased selection for areas with higher forage quality, suggesting that elk did not compromise access to nutritional resources during the archery season. Elk with higher‐risk home ranges were also exposed to the poorest nutrition and increased their selection for areas with higher forage quality more strongly than elk with lower‐risk home ranges during the hunting season. Elk with lower‐risk home ranges had access to the highest nutrition, which may be due to the availability of concentrated sources of high‐quality forage from irrigated agricultural areas on private lands that restricted hunter access. Resource agencies interested in encouraging elk to remain on public lands during the hunting seasons might consider closing motorized travel during the archery season to increase security on public lands, limiting hunter pressure on public lands, improving forage quality on public lands, and working with private land owners to enhance hunter accessibility and restrict elk access to high‐quality forage resources. © 2019 The Wildlife Society. Wildlife managers interested in encouraging even distributions of elk across landscapes during the fall archery hunting season may consider a combination of strategies focused on managing forage and security resources for elk across public and private lands. These strategies may include improving forage on public land, restricting access of elk to forage on private land, closing roads to motorized roads at the onset of the archery season, and increasing public hunter access to private lands. [ABSTRACT FROM AUTHOR]

Ungulates typically migrate to maximize nutritional intake when forage varies seasonally. In western North America, however, increasing numbers of ungulates reside on low‐elevation winter range year‐round rather than migrating. These residents often occupy irrigated agricultural areas, but it is not known whether the nutrition provided by agricultural land exceeds that gained by migration. We evaluated the nutrition available to a partially migratory population of elk (Cervus canadensis) in west‐central Montana where some individuals summered on low‐elevation agricultural lands, whereas others summered on traditional higher‐elevation ranges. We sampled elk forage plants from ground plots and adult female elk movements from global positioning system (GPS) collar locations during late summer for 2 years. We tested for differences in the nutrition provided by 11 vegetative communities commonly available to elk in the Rocky Mountains and the nutrition available in areas used by individuals whose behaviors ranged from residency to migration. We found the nutrition available to elk decreased along the continuum from resident to migratory behavior, contrary to our hypothesis that all behaviors would provide access to equivalent forage quality. The relatively small summer home ranges of migrants suggest other factors (e.g., decreased competition) may compensate for their lower nutritional value, because the size of a home range is often inversely related to its fitness benefits. We found irrigated agriculture provided the highest forage quality in low elevations, but recently burned (1–6 yr prior) dry forests at higher elevations provided forage quality approximately equivalent to that of irrigated agriculture. Excluding elk from irrigated agricultural areas should therefore reduce nutritional incentives for elk to reside at low elevations year‐round. Additionally, fire in higher‐elevation dry forests may temporarily increase forage quality for elk and improve nutritional benefits of migratory behavior. Our results indicate land management practices can affect nutritionally mediated fitness benefits of differing behaviors in partially migratory populations of ungulates. © 2018 The Wildlife Society. Nutrition available to elk during late summer decreased along the continuum from resident to migratory behavior in a partially migratory population in west‐central Montana, USA. Relatively high forage quality in irrigated agricultural areas contributed strongly to these nutritional differences, although recently burned higher elevation forested areas dominated by Douglas fir or Ponderosa pine provided forage quality equivalent to that of irrigated agriculture. [ABSTRACT FROM AUTHOR]