Migrations of diverse wildlife species often converge in space and time, with their journeys shaped by similar forces (i.e., geographic barriers and seasonal resources and conditions); we term this “co-migration.” Supporting this, recent studies have elucidated co-migrations and seasonal patterns that govern the location and timing of multiple species’ journeys. Beyond their significance as natural wonders, species with overlapping migrations may interact ecologically, with potential effects on population and community dynamics. Direct and indirect ecological interactions including predation and competition between migrant species remain poorly understood, in part because migration is the least-studied phase of animals’ annual cycles. To address this gap, we conducted a literature review to examine whether animal migration studies incorporate multiple species and to what extent they investigate interspecific interactions between co-migrants. Following a key word search, we read all migration research papers in 23 relevant peer-reviewed journals during 2008-2017. Thirty percent of animal migration papers reported two or more species with coinciding migrations, suggesting that co-migrations are common, although few studies investigated or discussed these mixed-species migrations further. Synthesizing those that did explore this phenomenon, we present examples and describe five types of ecological interactions between migrating species, including predator-prey, host-parasite, and commensal relationships. Deepening ecological knowledge of interspecific interactions among migratory animal communities will enhance understanding of the drivers of migration and could improve predictions about wildlife responses to global change. Further research focused on multi-species migrations could also inform conservation efforts for migratory animal populations, many of which are declining or shifting, with unexplored consequences for other co-migratory species.

We used the keyword “migration” to identify animal migration research papers published during a 10-year period (2008-2017). We selected 23 journals to capture a diversity of animal migration studies, including two journals focused broadly on biology (Proceedings of the Royal Society Biological Sciences, Global Change Biology); nine on ecology (Ecography, Ecological Applications, Ecology, Ecology Letters, Journal of Ecology, Journal of Animal Ecology, Oecologia, Oikos, Marine Ecology Progress Series); three on behavior (Animal Behavior, Behavioral Ecology, Behavioral Ecology and Sociobiology); three on conservation and management (Biological Conservation, Conservation Biology, Journal of Wildlife Management); two on movement (Animal Migration, Movement Ecology); and four that are taxa-specific, for birds (The Auk: Ornithological Advances), insects (Annual Review of Entomology), mammals (Journal of Mammalogy), and fishes (Fisheries and Oceanography). We read the introductions of all papers from the keyword search to verify their focus on the migratory phases of animal annual cycles, inclusive of staging and stopover sites. Next, we read the entirety of each identified paper and recorded geographic and taxonomic focus. Publications incorporating two or more species with co-occurring migrations were classified as “co-migration studies” either if a potential interaction between species was the focus of research or if the possibility of an interaction was discussed in the paper. For the purposes of the literature review, we did not include interactions among migratory species during stationary or resident phases (e.g., breeding or overwintering seasons). Our intention was to focus on species with overlapping spatiotemporal patterns in their migratory journeys and how they interact. We excluded review papers but included meta-analysis and modeling papers. We categorized co-migrant interactions by type.