Paper Proposes Framework for Future Study of “Co-Migration”

While the evolving COVID-19 crisis captures our attentions and dramatically impacts our daily lives, the seasons continue to change, bringing with them the return of robins and other birds, as well as insects, to our backyards.  Each spring around this time, prompted by seasonal changes in the availability of food, length of day, and temperatures, many species of mammals, birds, insects, and fish, make epic journeys by land, air, or sea from southern wintering areas to breeding locations further north. These animals are oblivious to how the current COVID-19 crisis has forced numerous changes to the ways of life of humans, such as social distancing, avoiding travel, and cancelling events where people congregate in numbers. Indeed, COVID-19 has forced professors and students at the Frostburg-based Appalachian Laboratory of University of Maryland Center for Environmental Science (UMCES) to take learning online and researchers to abide by restrictions on all research activities that require a physical presence at a campus or field site until further notice. Fortunately, while teleworking from home, our scientist are able to continue to find new insights into our surrounding natural world.

A recent paper by UMCES Appalachian Laboratory scientist Emily Cohen and co-author Dara Satterfield (Smithsonian Conservation Biology Institute) proposes a new framework to help researchers better understand and study communities of migrating animals. These migratory journeys are often collective with many species migrating at the same time and converging in the same places along the way, a phenomenon Cohen and Satterfield term “co-migration.” Due to the difficulty and cost inherent in tracking and monitoring animals across oceans or vast distances of land, co-migration has been historically understudied in ecology.

This lack of research on such an important annual occurrence is problematic because scientists do not fully understand how one animal species may impact or rely on other species during their migrations.  In other words, changes in one species may affect other species that travel with them, and that may mean a change in approach for species conservation efforts, which tend to focus on one species at a time.  A more holistic approach, prioritizing conservation across species and focusing on important places of convergence during migrations, may be needed.  Fortunately, new technologies, such as weather surveillance radar networks that can record detailed information about migrating birds, bats and insects over large areas of land and real-time satellite tracking of individually tagged animals, now make it possible to study co-migration at both the community and individual animal levels.

Co-migrations like the parade of goldfinches, doves, butterflies, dragonflies, and hoverflies observed by the famous biologists David and Elizabeth Lack flying over Pyrenees Mountains during the fall of 1950, are majestic. Yet, beyond noting their significance as natural wonders, we have rarely studied migrating animals as communities. If co-migration interactions affect migratory routes, phenology, or success, then shifts or declines in one migratory species may alter the migrations of other animals.

Dr. Emily Cohen

Figure depicting migration interactions

Examples of five types of interspecific interactions during migration demonstrating the geographic and taxonomic diversity of co-migrations (with symbols denoting positive, negative or neutral effects on species).

Based on findings from a review of ecology studies published by twenty-three journals over a ten-year period (2008-2017), Cohen and Satterfield developed a conceptual framework to guide and encourage future research on co-migration. As part of their review, Cohen and Satterfield quantified how often researchers report co-migration and the extent to which these co-migrations are included in analyses. They found most interactions during co-migration fell into one of five categories: (1) competition for resources such as food or habitat, (2) predator-prey interactions, (3) host-parasite interactions, (4) use of social information such as songbirds responding to calls from other species, and (5) feeding or habitat facilitation, as happens when wildebeests graze down grasslands to stimulate the growth of vegetation eaten by gazelles.  They propose these categories as a framework for researchers to direct and organize future research efforts on communities of migrating animals.

According to Cohen, “Human activities are increasingly challenging the existence of animal migrations as we are seeing enormous declines in the migratory individuals that cross vast distances and rely on multiple habitats throughout their life cycles. Studying migratory animals as communities could enhance our ability to conserve migratory species through identification of flyways and hotspots to prioritize conservation efforts across species. The good news is that it is increasingly possible to study these interactions today.”

Cohen and Satterfield are finalists for The Ecography Award for Excellence in Ecology and Evolution, an early career award for research scientists who publish an exceptional review on spatial and/or temporal patterns in ecology or evolution. Their paper, ““Chancing on a spectacle:” co-occurring animal migrations and interspecific interactions” will be published in the next edition of Ecography and can be read here. To learn more about Emily Cohen’s research at the Appalachian Laboratory visit her research website.