Conservation and management of migratory animals has gained attention in recent years, but the majority of research has focused on stereotypical ‘migrant’ and ‘resident’ behaviors, often failing to incorporate intermediate behaviors that may be more common. With migratory behavior threatened by anthropogenic development and climate change, it is crucial that we understand the full range of migratory behaviors. Our objective was to develop standard, reproducible methods to categorize the full range of migratory behaviors, including the extremes of the migratory continuum as well as intermediate strategies. We categorized annual movement trajectories of female mule deer (Odocoileus hemionus), one of only a few ungulates in North America that maintains long-distance migration. We created explicit definitions of movements that could be considered typical or “classic” migration, and parameters that can be used to describe and compare these, such as the departure day and arrival day during both fall and spring, and the length of time spent on the summer and winter range. We developed new categories for individuals that did not fall in the typical migrant or resident categories, by defining parameters such as the length of migration, the number of different ranges used and the number of trips to each range.
Results/Conclusions
We classified 648 annual migratory trajectories of 390 adult female mule deer, and found that 52% (n = 335) comprised typical behaviors, including residents (n = 64, 9.88%), stopover migrants (n = 86, 13.27%), and direct migrants (n = 185, 28.55%). The remaining 48% of migratory trajectories were atypical and we categorized them as brief migrants, which made migrations shorter than 3 months (n = 53, 8.18%), asynchronous migrants, which made migratory trips outside of typical fall and spring periods (n = 30, 4.63%), gradual migrants, which made gradual range shifts instead of direct movements between ranges (n = 35, 5.40%), commuting migrants, which went back and forward between the same two ranges multiple times (n = 7, 1.08%), and multi-range migrants, which used more than two ranges annually (n = 187, 28.86%). We conclude that the substantial number of atypical migratory strategies underlines the importance of studying these less-stereotyped behaviors exhibited by a large proportion of migrants, representing an important part of the population. Acknowledging and investigating the full complexity and diversity in migratory strategies might reveal unknowns on the underlying factors and drivers of migration, and can help shape effective conservation and management plans for entire populations.