Factors influencing pronghorn migration behavior and plasticity

Abstract

Variation in animal migration behaviors can improve population-level resiliency to unpredictable resource and environmental changes. Individuals of some species can switch migration behaviors, thereby optimizing individual fitness through plastic responses to environmental stochasticity and contributing to population resiliency. Pronghorn (Antilocapra americana) demonstrate variation and plasticity in migration behaviors across much of their range, yet the environmental, demographic, and anthropogenic influences on their migration decisions remain poorly understood. This study (2019–2023) analyzed collar location data from 516 adult female pronghorn across eight herds occupying a broad environmental gradient in Montana, USA, to characterize spring migration behaviors and evaluate environmental, demographic, and anthropogenic drivers of migration behavior, winter range plasticity, and migration behavior plasticity. Pronghorn exhibited varied migration behaviors: the majority were nonmigratory, either remaining as residents (77% of 1010 animal-years) or exhibiting gradual range shifts (11%), while others employed migrations to single (18%) or multiple (4%) summer ranges. We observed plasticity in migration behaviors, with 5.5% (of 382 animal-years) of pronghorn switching from nonmigrant to migrant behaviors and 27.7% (of 112 animal-years) switching from migrant to nonmigrant behaviors. Winter range fidelity also showed plasticity, with 84.6% remaining on or returning to their initial winter range, while the remainder shifted to new winter ranges. Our findings provide novel insights into pronghorn migration behaviors, highlighting the influence of both environmental and anthropogenic factors on migration behavior and plasticity. The probability of a migrant behavior increased with winter–spring precipitation and road density, and decreased with green-wave strength (e.g., greater values indicating a more consecutive or wavelike plant green-up across the landscape) and agricultural subsidy. Agricultural subsidy was also associated with a higher probability of switching from migrant to nonmigrant behaviors, suggesting that it may diminish the need for spring migrations by providing consistent forage. The observed migration plasticity suggests adaptive capacity in pronghorn populations occupying montane-valley and prairie environments, enabling them to navigate variable and human-altered environments. These findings underscore the importance of conservation strategies that prioritize landscape connectivity and allow pronghorn populations to maintain plastic migration strategies, accommodating their responses to changing environmental and human pressures.