Wood bison migration metrics and environmental covariates

Migration is an evolutionarily stable adaptation when movement costs are
outweighed by fitness gains. Migration is defined as the predictable
movement between seasonal ranges in response to differential resource
availability. However, migrations to locate suitable mates, and calving or
nursery grounds are also common across taxa. For ungulates, the growth of
new vegetation (i.e., green-wave) has been identified as a key mechanism
influencing migration between seasonal ranges. We investigated how the
green-wave influenced migration in a wood bison (Bison bison athabascae)
population in northern Alberta, Canada, while also considering risk of
calf predation by wolves (Canis lupus). Each year, all collared females in
the population migrated an average of 28-kilometers over 6-days to a
region at the western edge of their annual range between late-May and
early-June. By late-June they migrated back to their core range, averaging
a 40-kilometer migration distance over 10-days. We found that the
green-wave influenced both the timing of migration and selection of
habitats during migration. Risk of predation was not found to influence
habitat selection during migration. However, the herd congregating and
leaving their spring range as a group suggests risk of predation may be an
evolutionary mechanism contributing to this migratory behavior. The timing
of migration and congregation aligns with the expected timing of
parturition giving further support that both the green-wave and predation
risk influence migration. We provide a framework to assess interrelated
mechanisms influencing migration, which is important to those studying,
managing, and/or conserving migratory ungulates.