Native forage mediates influence of irrigated agriculture on migratory behaviour of elk

• Published in: The Journal of animal ecology 2019-07, Vol.88 (7), p.1100-1110
• Main Authors: Barker, Kristin J., Mitchell, Michael S., Proffitt, Kelly M.
• Format: Article
• Language: English
• Subjects: agricultural subsidy; Agriculture; Animal Migration; Animals; Anthropogenic factors; Cervus canadensis; Cervus elaphus; Deer; Density; Ecosystem; Elk; Environmental conditions; Female; forage maturation; Growing season; Human behavior; Human influences; Humans; land use; Livestock; Livestock grazing; Migrants; Migration; Montana; partial migration; RESEARCH ARTICLE; Seasonal variations; Seasons; Summer; ungulate; Ungulates; Weather; Weather patterns; Wildfires; Winter
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.12991

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. Partial migration is common in ungulate populations, but the mechanisms driving variation in individual behaviours are poorly understood. This study found consistent influences of both native forage and irrigated agriculture on migratory behaviour of more than 300 elk in 16 herds across varying environmental conditions and anthropogenic influences.