Migration Matters

By Land, Air, and Water – USGS Science Supporting Fish and Wildlife Migrations Throughout North America

Countless species of animals – big game, birds, bats, insects, amphibians, reptiles, and fish – migrate to reach suitable habitats to feed, reproduce, and raise their young. Animal migrations developed over millennia oftentimes follow migration corridors—unique routes for each species and sometimes each population—to move among seasonal habitats.   

Some migrations happen on a grand scale.  Thousands of species of birds, bats, and butterflies take long migratory flights across North America and beyond, and these events are a source of recreation for millions of outdoor enthusiasts such as hunters, birders, and butterfly watchers.  Other migrations, such as those by amphibians, are much more localized and cover only a few meters to a few kilometers.  

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The four migratory bird flyways found in the United States from left to right: Pacific, Central, Mississippi, and Atlantic. Most northern hemisphere birds migrate southward, but there are many other ways that birds move seasonally. If we want to protect birds that take these long-distance journeys,  we need to understand why they move, why they stay, how they move, and why they go where they go . Data Source: U. S. Fish and Wildlife Service.

Working on Their Night Moves

Many species of amphibians and reptiles - frogs, toads, salamanders and tortoises - migrate to breeding locations during the spring and summer months. Movements at night increase mortality from vehicle strikes. While most people associate vehicle strikes with mammals, many amphibians and reptiles are either too small or too slow to avoid oncoming traffic. 

Migrate for a Mate

In the desert Southwest, increasing demand for renewable energy, housing, recreation, and military training sites is placing greater pressures on this ecosystem shared with the endangered Agassiz desert tortoise. The barriers created by these changes may make it harder for tortoises to find a mate.

The Development Dilemma

In the American West, man-made barriers that impede movements of migrating ungulates – hooved animals such as elk, mule deer, caribou, and pronghorn – make it harder for herds to complete their annual migrations. When migrating herds encounter residential housing, energy development, and other barriers such as roads and fences, their feeding behavior can change, and they lose the benefits of migration, threatening the long-term persistence of migratory corridors. 

Economic Benefits of Conservation

Animals migrate seasonally between habitats to reach resources where and when they are most abundant. The benefits we derive from migratory species are economically and culturally important; they include food for millions of people, regulation of agricultural pests, pollination, recreation (wildlife viewing, hunting), seed dispersal, and many more. 

In 2020, 53 percent of Americans ages 6 and over participated in outdoor recreation at least once, including wildlife viewing, bird watching, hunting, fishing or photographing fish and other wildlife. This was the highest participation rate on record with 7.1 million more Americans participating in outdoor recreation than in the year prior. Often these activities are on Department of the Interior managed places such as national parks and wildlife refuges that maintain intact ecosystems for wildlife to thrive.  In 2021 these pristine landscapes attracted an estimated 494 million visits which supported an estimated $37.9 billion in economic output, and about 484,000 jobs.  

Mighty Monarch Migrations

Monarch butterflies from the central U.S. and Canada undertake spectacular migrations, flying an impressive 2800 miles each fall to overwinter in central Mexico, while west of the Rockies monarchs overwinter in groves along the California coast. These journeys are being disrupted by large gaps in needed habitat, exposure to herbicides and pesticides, or by extreme weather; collectively these threats have resulted in an approximately 80 percent decline in the eastern migratory population.

The Big Year

The U.S. Fish and Wildlife Service lists over 1,000 species of migratory birds in North America. Each year they migrate in the spring and fall to reach roosting and breeding areas. Migratory birds provide ecosystem benefits that include pest control, pollination of plants and serve as food sources for other wildlife. They are also a source of recreation for millions of bird watchers and enthusiasts who provide food and design backyard habitats to attract a variety of species throughout the year.  Climate change, habitat loss, disease, and energy development all pose challenges for migratory bird populations. 

Flying Agronomists

Many of the 47 species of bats in North America migrate in the spring and fall to reach roosting and breeding areas. Insect-eating bats provide pest control and pollination services worth billions of dollars to farmers annually, but bat populations nationwide are being threatened by an invasive fungal disease (white-nose syndrome), wind turbines, habitat loss, and other stressors. 

Migration Science to Support Management Decisions 

Changes along migration corridors, whether from infrastructure we rely on (buildings, roads, dams) or increased natural disturbances because of climate change (for example, drought, fire, flooding, or invasive species), can make them harder to navigate.  Conservation efforts are more successful and effective when rooted in science that can measure their effectiveness and test new approaches.  The U.S. Geological Survey (USGS) provides science that assists natural resource managers in mapping, enhancing, protecting, and reconnecting migration corridors critical for diverse fish and wildlife populations that migrate, such as mule deer and pronghorn, trout and salmon, salamanders, tortoises, bats, and monarch butterflies. 

Energy Development

Wind, Solar, and Hydropower  

Energy development is booming across the United States, helping to secure plentiful energy to meet our nation’s needs. Yet energy generation can sometimes have adverse effects on ecosystems and wildlife, including migratory pathways.  From assessing which migratory species are most susceptible to impacts from wind turbines to developing new methods to monitor wildlife activity around utility-scale solar power to creating new technologies that facilitate fish migration near hydropower dams, USGS research is instrumental in creating “smart solutions” to help reduce the risks, as well as the costs, of domestic energy development. 

VIDEO: Surveillance video from a temperature-imaging camera showing a bat interacting with a wind turbine. It’s possible that wind turbines interfere with seasonal migration and mating patterns in some species of bats. More than three quarters of the bat fatalities at wind turbines are from species known as “tree bats,” which tend to migrate long distances and roost in trees. These bats migrate and mate primarily during late summer and early autumn, which is also when most bat fatalities at wind turbines occur. It’s also possible that bats mistake slow or stopped turbine blades for trees.

A male Agassiz's desert tortoise, equipped with a transmitter, in a wind energy facility near Palm Springs, California. An important measure of the impact of renewable energy development on wildlife is direct mortality, but accurately estimating it is difficult when mortality takes place over an extended period, and probability of discovery of fatalities varies greatly. Over the last several years, the USGS has developed more accurate  fatality detection tools and monitoring protocols  to assist both the solar and wind energy industry and the agencies that regulate their development and operations.

Climate

From the expansion of invasive species to wildfire, from drought to sea-level rise and flood events, changes in climate have created new challenges for migratory species. Some species may move to more-favorable habitats, others may change their behavior (such as by shifting their diets), and still others may change the timing of life-cycle events (such as migration). Rapidly changing climate conditions are impacting the quality and availability of migration routes. USGS science seeks to better understand how climate change impacts migrations and helps to quantify and predict interactions between climate, habitats, and migratory species. 

MAP: Early fall wildfires in the western states and the smoke they generate pose a risk to birds migrating in the Pacific Flyway.  GPS data from the 2020 wildfire season indicate that at least some migratory birds may take longer and use more energy to avoid wildfire smoke.  These energy deficits could lead to increased mortality or lower reproductive rates, suggesting that smoke disruptions could ultimately put vulnerable migratory bird populations at greater risk.

Movement patterns of GPS-collared elk over time in southwestern Wyoming. Climate-driven changes in vegetation can influence migration timing and patterns. Source:   https://pubs.er.usgs.gov/publication/70203052 

Environmental Contaminants

Exposure to environmental contaminants, such as pesticides, herbicides, and pharmaceuticals, can have varying effects on an animal’s physiology, thus affecting their ability to successfully migrate, mate, and find food. USGS environmental health science supports integrated natural science expertise and capabilities related to environmental contaminants and pathogens. This science informs stakeholder decisions to manage fish and wildlife health and provides environmental exposure information to partners in public health.   

PHOTO: Manatees need warm water to survive and, in Florida, migrate to warmer inland waters in the winter. For nearly four decades, the U.S. Geological Survey's  Sirenia Project  has been committed to understanding the biology and ecology of the West Indian manatee to aid managers in actions that could best help the population. 

The Indian River Lagoon in eastern Florida is a critical habitat for the Florida manatee (Trichechus manatus latirostris ). However,  the Indian River Lagoon has experienced a substantial decline in seagrass due to the persistence of several harmful algal blooms.  Seagrass loss in has been so extensive that manatees were observed feeding in locations that were so shallow that they were partially exposed.

Two manatees with radio transmitters attached

Water Management

Habitat fragmentation due to dams and poorly designed stream-crossings has significantly contributed to severe declines in recreational, commercial, cultural, and ecologically important fish species. Because there are tremendous variations between physiology and behavior of migratory fish, in the size and structure of dams, and in the rivers themselves, there is no ‘one-size-fits-all’ to facilitate fish passage through barriers.  The ability of fish to successfully use fishways, and complete their migration and reproductive cycles, is determined by assessing their ability to move between rivers and oceans, and their ability to reproduce as conditions change in rivers (temperature and flow rate) and coastal waters (ocean acidification, salinity, temperature). The USGS provides tools and strategies to help managers understand the effects these barriers have on migratory fish and maintain and restore thriving fish populations and aquatic ecosystems. 

MAP: Fishways in the Eastern United States. Fishways are structures that have been built to give fish a path to swim around barriers to migration, such as dams. 

Left:  Prototype Acrylonitrile butadiene styrene (ABS) plastic eel climbing ramp under development and testing . The substrate design allows for passage of a wider size range of eels with less need for precise flow regulation. Right: juvenile eel climbing wetted ABS plastic substrate. The American eel (Anguilla rostrata) migrates into freshwater as a juvenile, feeds and grows in freshwater habitats, and migrates downstream to the ocean to spawn as an adult. Migrating eels frequently encounter barriers in river environments.

Transportation and Urbanization

Animals that migrate across land face unique challenges because their migratory paths often cross or are interrupted by roadways and other human developments. Not only does this development impede or alter migration routes, but in the case of road crossings, it also can be a dangerous situation for animal and human. USGS scientists are working with Federal, State, and private entities to provide solutions and mitigate these roadway hazards. For small animals, human developments can be an even bigger challenge, limiting seasonal movements to reach critical habitat for breeding. The USGS is improving our understanding of how certain species are connected across the landscape at different times of the year and is developing strategies that provide options for safe migration routes that avoid barriers to movement. 

MAP: Movement pattern of a pronghorn affixed with a GPS collar. The 11-month migration pattern illustrates barriers pronghorn face in both migration routes and seasonal habitats, such as multiple highway crossings, navigating a gas field, and avoiding urban development.

Data source: Sawyer, H., Korfanta, N.M., Kauffman, M.J., Robb, B.S., Telander, A.C. and Mattson, T. (2022), Trade-offs between utility-scale solar development and ungulates on western rangelands. Front Ecol Environ, 20: 345-351.  https://doi.org/10.1002/fee.2498 

This video shows a California tiger salamander finding its way to an underpass designed to help amphibians and reptiles cross the road safely, with the help of a "turn-around" that helps guide the salamander back in the right direction as it travels away from the underpass. The salamander was caught on wildlife cameras at various points between the turn-around and the underpass as part of a USGS study to understand how California tiger salamanders use turn-arounds and passage structures. The study was part of a  larger project to develop science-based guidance for road agencies to help reptiles and amphibians cross roads safely .

Wildlife Disease and Transmission

USGS is leading research that provides baseline information on the health, behavior, and population status of migratory species throughout North America. One focal area of research is on the detection, spread, and control of diseases such as avian influenza in birds, chronic wasting disease in deer elk and other hooved animals, and white-nose syndrome in bats. This science is helping wildlife managers prevent the potential spread of these wildlife diseases through migratory pathways.  

MAP:  Distribution of Chronic Wasting Disease in North America . Chronic wasting disease (CWD) is an emerging infectious disease that is fatal to free-ranging and captive animals in Cervidae, the deer family. CWD is one member of a family of diseases called transmissible spongiform encephalopathies (TSEs) and is thought to be caused by prions. CWD is the only TSE known to affect free-ranging wildlife. 

Waterfowl migration patterns in the Pacific Flyway based on GPS data. USGS biologists   conduct research on migratory waterfowl and their habitats   to guide conservation programs in the Pacific Flyway.

Conservation Technology

To better conserve, support, and protect migrating species, we need to know where they are, how many there are, and how they are using habitats. USGS is deploying new cutting-edge technologies and approaches to detect, track and map wildlife species movements. Our scientists develop new methods and diagnostic tools, using everything from acoustics to environmental DNA to satellite transmitters, to obtain accurate and often near real-time data to track wildlife. Using high-performance computing, these data are used to predict animal movements under different habitat, climate, and land use scenarios. The species population assessments and long-term surveys that USGS science provides can act as early warning systems for changes in populations resulting from emerging threats. 

Journey from River to Sea

Chinook salmon are found from the west coast of North America to Russia’s Kamchatka Peninsula.  The largest of the Pacific salmon, many populations are listed as threatened or endangered. Juveniles live in freshwater habitats, migrate to the sea, then return to freshwater to spawn. Returning adults are powerful swimmers and some swim upstream hundreds of miles to reach their spawning grounds. Salmon play a critical role in supporting and maintaining ecological health, and in the social fabric of First Nations and tribal culture. Climate change, dams, habitat degradation, overfishing, and disease all contribute to declining chinook salmon populations. 

Climate Conditional

All seven species of sea turtles engage in migratory behavior. Some only travel short distances and some, like the leatherback, take long migratory journeys. Sea turtles migrate between feeding and nesting grounds, and some will migrate seasonally to warmer waters. Climate change may be putting endangered sea turtles at further risk by reducing the suitability of habitat for nesting and feeding.

Bull Trout

Bull trout are native to the northwest United States and western Canada. Bull trout can grow upwards of 15 pounds, require extensive, unfragmented stream networks, and migrate to spawn. Bull trout are primarily threatened by habitat degradation and fragmentation, blockage of migratory corridors, poor water quality, and the introduction of nonnative species such as brown and brook trout. 

Habitat Restoration / Species Recovery  

When migratory corridors or stopover habitats are interrupted due to land use change, fragmentation, or degradation, species struggle to feed, migrate, and reproduce. Maintaining a connected network of protected areas is important to prevent ecosystems and populations from becoming isolated, reduce the risk of extinction, and ultimately sustain biodiversity.   USGS science not only provides information and data to help resource managers make informed decisions for the successful management of species populations and habitats, it also aides wildlife in navigating some of these barriers to migration. Fish and wildlife are an integral presence in the fabric of American landscapes. Healthy wildlife populations sustain communities across the Nation and maintaining ecosystems thriving with biodiversity ensures these resources are available for generations to come. 


Migration Science Resources

Publications

By land, air, and water — U.S. Geological Survey science supporting fish and wildlife migrations throughout North America  https://doi.org/10.3133/fs20223030 

A male Agassiz's desert tortoise, equipped with a transmitter, in a wind energy facility near Palm Springs, California. An important measure of the impact of renewable energy development on wildlife is direct mortality, but accurately estimating it is difficult when mortality takes place over an extended period, and probability of discovery of fatalities varies greatly. Over the last several years, the USGS has developed more accurate  fatality detection tools and monitoring protocols  to assist both the solar and wind energy industry and the agencies that regulate their development and operations.

Movement patterns of GPS-collared elk over time in southwestern Wyoming. Climate-driven changes in vegetation can influence migration timing and patterns. Source:   https://pubs.er.usgs.gov/publication/70203052 

The Indian River Lagoon in eastern Florida is a critical habitat for the Florida manatee (Trichechus manatus latirostris ). However,  the Indian River Lagoon has experienced a substantial decline in seagrass due to the persistence of several harmful algal blooms.  Seagrass loss in has been so extensive that manatees were observed feeding in locations that were so shallow that they were partially exposed.

Left:  Prototype Acrylonitrile butadiene styrene (ABS) plastic eel climbing ramp under development and testing . The substrate design allows for passage of a wider size range of eels with less need for precise flow regulation. Right: juvenile eel climbing wetted ABS plastic substrate. The American eel (Anguilla rostrata) migrates into freshwater as a juvenile, feeds and grows in freshwater habitats, and migrates downstream to the ocean to spawn as an adult. Migrating eels frequently encounter barriers in river environments.

Waterfowl migration patterns in the Pacific Flyway based on GPS data. USGS biologists   conduct research on migratory waterfowl and their habitats   to guide conservation programs in the Pacific Flyway.