By Land, Air and Water: USGS Science for Migrating Fish and Wildlife

Countless animals — big game, birds, bats, insects, amphibians, reptiles and fish — migrate to find places to feed, breed and raise young. Over millennia each species has developed its own migration corridors between seasonal habitats. Changes along those routes, from buildings, roads and dams to the droughts, fires, floods and invasive species that a changing climate brings, can make them harder to travel. The U.S. Geological Survey (USGS) studies these journeys and how to keep them open.

Over land

Migration routes on land often cross roads and other development, which can block or reroute animals and make road crossings dangerous for animals and people alike. For small animals, development can cut them off from breeding habitat. USGS scientists work with federal, state and private partners on ways to reduce these hazards and keep safe routes open.

Surfing the green wave, and safer crossings

In the West, barriers made by people make it harder for herds of ungulates — hoofed animals such as elk (Cervus elaphus), mule deer, caribou (Rangifer tarandus) and pronghorn — to complete their migrations. USGS research in Wyoming showed that migrating ungulates follow the peak of fresh vegetation as it greens up in spring, a behaviour called "surfing the green wave." When herds run into housing, energy development, roads and fences, their feeding changes and they lose the benefits of migrating, which threatens the corridors' long-term survival.

With the University of Wyoming, the USGS developed a Migration Mapper that combines many animals' paths, from GPS collars, into maps of the corridors a whole population uses. Landowners, managers, policymakers, land trusts and hunting conservation groups now use such maps in planning.

GPS data from collared mule deer and pronghorn, analysed by the USGS, the University of Wyoming and the Wyoming Game and Fish Department, show that many migrating animals cannot cross busy major highways, and that smaller roads, though not yet barriers, kill many animals in collisions. State transportation planners are using this knowledge to build underpasses and overpasses where animals prefer to cross, making roads safer for drivers and wildlife. Nationwide, about 200 drivers and more than 1 million large animals die each year in collisions with wildlife.

Helping small animals across

Many frogs, toads, salamanders and tortoises migrate to breeding sites in spring and summer, often at night, and many are too small or too slow to escape traffic. The USGS and partners are testing new road designs and citizen-science efforts to cut these deaths.

A road sign in California marks habitat of sensitive amphibians, including the rare Yosemite toad (Anaxyrus canorus). USGS scientists helped the U.S. Forest Service launch a project testing whether low bridges over roadkill hotspots can protect Yosemite toads and other amphibians. Photograph by Cheryl Brehme, U.S. Geological Survey.

In the Northeast, spotted salamanders (Ambystoma maculatum) cross roads on spring nights to reach breeding pools, and mass deaths can follow. Community groups carry adult salamanders across roads on these "big nights." Scientists with the USGS Amphibian Research and Monitoring Initiative found that while this helps adults, helping juvenile salamanders across in summer, after they leave the ponds, would do even more for the population.

A small pond used by breeding salamanders, next to a road. Photograph by Evan Grant, U.S. Geological Survey.

In the desert Southwest, demand for renewable energy, housing, recreation and military training is squeezing habitat shared with the endangered Agassiz's desert tortoise (Gopherus agassizii), and the new barriers may make it harder for tortoises to find mates. With the University of Nevada, Reno, the Bureau of Land Management, the U.S. Fish and Wildlife Service and private industry, USGS scientists are studying how tortoises and other species are connected across the landscape, and whether conservation corridors can help keep populations genetically diverse.

Radio transmitters on adult tortoises let researchers follow their movements. Photograph by Zachary Cava, U.S. Geological Survey.

In the air

Thousands of species of birds, bats and butterflies migrate long distances across North America and beyond, to the delight of millions of hunters, birders and butterfly watchers. The USGS provides baseline information on the health, behaviour and population status of flying migrants, with a focus on detecting, tracking and controlling diseases such as avian influenza in birds and white-nose syndrome in bats, so managers can keep them from spreading along migration routes.

A USGS biologist releases a bat carrying a tiny radio transmitter; researchers increasingly use high-tech methods to learn about bats' secretive lives. The USGS co-leads the North American Bat Monitoring Program with the U.S. Fish and Wildlife Service to map bat distribution and abundance in the United States and Canada. Photograph by Ernie Valdez, U.S. Geological Survey.

Bird banding. The USGS Bird Banding Laboratory holds more than 100 years of information on birds' long-distance movements around the world. Supporting a wide research community, it reveals individual birds' migratory behaviour and life histories and the places critical for breeding, wintering and stopovers, and it supports banding that underpins sustainable harvest management and disease surveillance in migratory waterfowl.

Monarchs. Monarch butterflies from the central United States and Canada fly 2,800 miles each fall to winter in central Mexico; west of the Rockies, monarchs winter in groves on the California coast. Gaps in habitat, herbicides and pesticides, and extreme weather have together driven a nearly 80 percent decline in the eastern migratory population. The USGS leads the trinational Monarch Conservation Science Partnership, in which the United States, Canada and Mexico set research priorities for monarch ecology and conservation.

A monarch butterfly. Photograph by Mike Glenn, U.S. Fish and Wildlife Service.

Bats offshore. Many of North America's 47 bat species migrate in spring and fall. The USGS is studying how tall structures such as wind turbines affect tree bats that fly long distances south or to the coast, where some have been seen flying offshore. To gauge the risk from planned offshore wind farms, researchers placed acoustic recorders on structures such as lighthouses on Virginia's barrier islands. Bats visited offshore and barrier-island sites at night more often when wind was lower and temperatures and visibility higher, and visits varied with the season. The findings went into a tool that predicts where bats will occur at future offshore wind sites, helping the industry plan to reduce collisions.

Paired thermal-imaging cameras on wind turbines record the activity of bats, birds and insects to a computer inside the turbine's base. Photograph by Paul Cryan, U.S. Geological Survey.

Through the water

Rivers and streams are corridors for fish moving between fresh water and the sea, and between streams and lakes. Migratory fish — herring, sturgeon, paddlefish, trout and salmon — support commercial fishing and recreational angling worth billions of dollars to local economies. They face climate change, drought, habitat loss, invasive species, and barriers such as culverts and dams; more than 90,000 dams in the United States serve agriculture and hydropower. The USGS gives managers tools to understand how barriers affect migrating fish and to keep fish populations and aquatic ecosystems healthy.

• Reintroducing bull trout. Bull trout (Salvelinus confluentus) migrate through rivers and streams to use larger rivers, reservoirs, lakes and even the ocean. Where migrating fish do not recolonise on their own, recovery can mean capturing and moving them. USGS tools help managers judge habitat suitability and make these hard decisions, including for reintroductions in the Klamath and Willamette Rivers in Oregon and the Pend Oreille River and Lake Chelan in Washington, and a move of bull trout to a new location in Glacier National Park, Montana.
• Fish passage for eels. The American eel (Anguilla rostrata) lives along the Atlantic coast of the United States and Canada and inland in the Great Lakes and much of the East. Young eels travel from the ocean up rivers to feed and grow, and adults return downstream to the sea to spawn. Dams with turbines and spillways threaten both journeys, and USGS research is designing safe, timely passage for young and adult eels.
• Salmon after dam removal. For decades the Elwha and Glines Canyon Dams on Washington's Olympic Peninsula blocked salmon from the river and tributaries above them. The dams were removed to restore habitat important to the peninsula's communities, culturally and economically. Afterwards, thousands of Chinook salmon (Oncorhynchus tshawytscha) swam upstream to spawn above the former Elwha Dam for the first time in more than a century. USGS studies of the removal give a strong scientific basis for dam removals elsewhere.

Glines Canyon Dam, built in 1927 in Olympic National Park, during its deconstruction by "notching down," in a webcam photograph of February 7, 2012. Credit: National Park Service.

A USGS scientist with a Chinook salmon carcass found upstream of the two removed dams on the Elwha River. Restoration let salmon reach upstream spawning grounds for the first time in more than a century; after spawning, salmon die and become food for many animals. Photograph by Joshua Logan, U.S. Geological Survey.

Sources

Based on "By Land, Air, and Water—U.S. Geological Survey Science Supporting Fish and Wildlife Migrations Throughout North America," by Mona Khalil, Mark Wimer, David Hu, Mike Adams, Melanie Steinkamp and Suzanne C. Soileau, U.S. Geological Survey Fact Sheet 2022–3030, published by the U.S. Geological Survey; rewritten in hubnx's own words.

• The photographs and the captions' facts come from the fact sheet's PDF: https://pubs.usgs.gov/fs/2022/3030/fs20223030.pdf
• The fact sheet cites Middleton and others (2018), Sterrett and others (2019), Tracy and others (2019), True and others (2021), Wieferich and others (2021), Huijser and others (2008) and Normand (2021).
• Its stock photographs, credited to iStock, are not reproduced.