Introduction
Since the Upper Paleolithic age more than 20,000 years ago, humans have
been fascinated by animal movement, as evidenced by early rock art
depicting animal migration
(Bacon et al., 2023).
From this long-standing interest in animal movement has come a rich
history in studying animal migration. Most studies of animal migration
have primarily focused on latitudinal migration, although altitudinal
migration—the seasonal movement of populations across elevational or
bathymetric gradients (Hsiung et al., 2018; Milligan et al., 2020)—has
garnered increasing attention across taxonomic groups. Altitudinal
migrants often pass through multiple habitats with different
environmental conditions and experience a similar or even greater
breadth of ecological interactions (e.g., predation, interspecific
competition, interactions with parasites, etc.) compared to strict
latitudinal migrants (Williamson & Witt, 2021). As the taxonomic
representation of studies on altitudinal migration has grown, so too
have inconsistencies in the language used to describe this phenomenon.
Here we propose a functional definition of altitudinal migration and
provide guidelines towards a unified conceptual framework of altitudinal
migration that highlights its biological importance and prevalence
across taxa (Figure 1). We also discuss emerging opportunities and
challenges, outstanding questions in the field, and future directions to
advance its study. Collective thought towards an improved conceptual
framework will enable researchers to better compare and contrast
emergent patterns and identify idiosyncrasies of altitudinal migration
behavior among taxa and biogeographic regions.