The study and importance of altitudinal migration has attracted
increasing interest among zoologists. Altitudinal migrants are
taxonomically widespread and move across environmental gradients that
transect altitudinal and latitudinal gradients as partial or complete
migrants, subjecting them to a wide array of environments and ecological
interactions. Here, we present a brief synthesis of recent development
and suggest future directions towards a more taxonomically inclusive
conceptual framework for the study of altitudinal migration. Our
framework centers on a working definition of altitudinal migration that
highlights the biological relevance and scale of movement for a given
taxon and its life history. Even with a revised definition, however, the
distinction between the narrower phenomenon of migration and wider study
of movement often blurs. We discuss nuances of altitudinal movements and
encourage comparisons among taxa from divergent lineages and biomes that
encounter different ecological interactions and physiological challenges
across their annual cycles. We also summarize new opportunities,
methods, and challenges for the ongoing study of altitudinal migration.
A persistent, primary challenge is characterizing the taxonomic extent
of altitudinal migration within and among species. Fortunately, a host
of new methods have been developed to help researchers assess the
taxonomic prevalence of altitudinal migration---each with their own
advantages and disadvantages. An improved conceptual framework of
altitudinal migration will allow researchers that study disparate
disciplines and taxonomic groups to better communicate and operate in a
comparative framework to test hypotheses regarding the evolutionary and
ecological drivers underlying variation in altitudinal migration among
populations and species.