The Role of Lakes in Bird Migration

Twice a year, billions of birds embark on one of nature's greatest wonders—migration. In the spring, they fly to their nesting grounds, and in the fall, they travel to warmer climates to survive the harsh winter. Along these migration routes, lakes play a central role. They provide food, resting places, and cover for birds that must fly thousands of miles across varied landscapes. For certain birds, a chain of healthy lakes can mean the difference between surviving and exhausting themselves. Learn more about the role of lakes in bird migration.

Why Lakes Matter to Migratory Birds

Migration takes enormous amounts of energy. Birds must refuel frequently, resting at sites along the way where food is abundant and there are safe places to rest. Lakes serve these purposes by offering open water, fertile feeding areas, and wetlands that shield from predators.

For waterbirds such as ducks, geese, and swans, lakes are not simply refueling stations but wintering sites. Shorebirds and songbirds rely on lakes, too, and they find insects and aquatic plants along the shores. Without lakes, migratory routes would be disrupted, and many species would be unable to complete their journeys.

Stopover Sites: Nature's Refueling Stations

The concept of a "stopover site" is at the core of migration. Birds cannot continue to fly, so they seek sites with plentiful food and minimal disturbance. Lakes are just what they need.

During fall migration, for example, southbound ducks migrating from Canada may make a stopover on Midwest lakes to feed on aquatic plants and invertebrates. Stopovers offer them the luxury of building up fat stores before continuing on to Gulf Coast or further inland wintering grounds in Central and South America.

Small lakes are important if they run along a main flyway. A single healthy wetland can host tens of thousands of birds at once.

Principal Flyways of the United States

North America is divided into four broad migratory flyways: the Atlantic, Mississippi, Central, and Pacific. Lakes along these routes are important stopovers.

• Along the Maine-to-Florida corridor in the Atlantic Flyway, wetlands and lakes support waterfowl, shorebirds, and songbirds migrating between Arctic breeding grounds and South American wintering areas.
• The Mississippi Flyway includes the Great Lakes, the globe's most important system of freshwater for migratory birds. Millions of geese, ducks, and swans congregate every fall and spring to feed and relax there. The size and diversity of these lakes make them unavoidable for long-distance migrants.
• The Central Flyway consists of the prairie pothole region, a string of small glacial lakes dispersed throughout the Dakotas, Minnesota, and southern Canada. The Prairie Pothole Region is "North America's duck factory," raising and sustaining more waterfowl than any other habitat on the continent.
• Along the Pacific Flyway, the Salton Sea in California is an important stopover for pelicans, cormorants, and shorebirds. Despite shrinking size and water quality problems, it remains a vital stopover in an otherwise desert setting.

Challenges and Threats

Lakes are vital to bird migration, but they are stressed ecosystems. Human development, pollution, and climate change threaten to cut short or end their ability to support migratory birds. If a couple of stopovers on a flyway are lost, the impacts sound throughout entire bird populations.

Habitat Loss

Habitat loss is likely the most serious threat. Shoreline development for housing, marinas, and agriculture often eliminates wetlands that birds rely on for resting and feeding. According to the US Fish and Wildlife Service, the lower 48 states have lost more than 50% of their original wetlands since the 1780s, much of it converted for farmland or urban use. In the Prairie Pothole Region—"North America's duck factory"—half of all wetlands are estimated to have been drained, translating to fewer areas where waterfowl can breed or stop over during migration.

Pollution

Pollution only compounds these losses. Nutrient runoff from fertilizers results in poisonous algal blooms, such as those that plague Lake Erie. In 2014, a massive bloom led half a million Toledo, Ohio, residents to avoid drinking water for several days. These aquatic organisms draw oxygen from the water, poison fish, and disrupt food webs that migratory birds depend on. Toxic chemicals like mercury and pesticides also concentrate in lakes, which can impair bird reproduction and chick survival. A 2009 Environmental Protection Agency (EPA) study showed mercury contamination in almost 50% of US lakes.

Climate Change

Global climate change alters lakes in a fundamental way. Rising temperatures drive evaporation, lowering the water levels of shallow wetlands. Global lakes are warming at an average rate of about 0.61°F (0.34°C) per decade (according to Geophysical Research Letters). At higher latitudes, altered precipitation patterns have the potential to induce flooding in lakes one year and dryness in the next, making migratory birds unable to rely on long-standing locations that have traditionally been there.

Disturbance

Human disturbance is another growing threat. Recreational boating, jet skiing, and fishing derbies commonly overlap with migration periods. In sections of Minnesota's lake country, for example, heavy boat traffic during spring and fall can displace thousands of waterbirds from feeding grounds before replenishing their energy. Certain key habitats, such as sections of the Upper Mississippi River National Wildlife and Fish Refuge, restrict boat traffic during migration, allowing resting birds to remain undisturbed.

Disturbances affect single birds and have a ripple effect on populations. Flocks that are forced to expend extra energy might ultimately arrive at breeding grounds in poorer condition, reducing their chances of nesting successfully.

Conservation and Management

Bird migration conservation is both local and global. Birds don't recognize political boundaries, and their survival depends on coordinated conservation across entire flyways.

In the United States, state and local government agencies identify "Important Bird Areas" (IBAs) around lakes for long-term protection, while government programs such as the North American Waterfowl Management Plan and the National Wildlife Refuge System protect large lake and wetland ecosystems.

Community action at the local level is also needed. Reducing fertilizer use, restoring wetlands, and confining shoreline development make lakes healthier. Private-landowner agreements and conservation easements expand protected habitats beyond what the public owns.

Lakes are essential to the survival of migratory birds. They are sources of food, relief, and safe crossing over long distances, acting as way stations on journeys spanning continents. From the Great Lakes to the prairie potholes to the Salton Sea, these lakes are lifelines in the great flyways of North America. Conservation is key if migration is to remain among the Earth's enduring natural wonders. Preserving lakes ensures that the skies remain full of activity every fall and spring, linking ecosystems worldwide through the wings of flying birds.