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Shorebird Habitats
Habitat
A habitat is the place where an organism obtains energy (food) and water and finds shelter. Without suitable habitat, the organism would die. Plants, animals, and all other organisms are adapted to live in a particular type of habitat. Terrestrial habitats may be hot or cold, dry or wet, with sandy soils or peat, and include endless other characteristics. Aquatic habitats may be salt or freshwater, shallow or deep, warm or cold, just to begin describing them. Plants generally only live in one habitat in their lifetimes, but animals that can move large distances might use several.
Migration
Migration is when an animal moves from one place to another, often from one habitat to another. Usually migration refers to a somewhat predictable pattern of such movement. Some planktonic organisms migrate up and down in the water in response to the amount of daylight. In turn, some fish migrate up and down in response to the migration pattern of these plankton upon which they feed. Animals may migrate because of changes in season, food availability, or number or success of competitors. How are these different reasons related to each other? Can you think of any other reasons for migration between habitats?
Significance for Shorebirds of Migration between Habitats
Birds are capable of the most advanced method of movement on earth: they can fly. Because of this ability, many of them have evolved to use more than one habitat. Arctic?nesting shorebirds undertake some of the longest migrations in the world. Many of them fly incredible distances each spring to nest on the arctic tundra, and then fly far south again in the fall to spend their "nonbreeding season" in a very different habitat. They do this in response to food availability, presence of fewer competitors in the Arctic, and weather change, all of which are very closely associated.
Shorebirds Habitats
In its most basic definition, the habitat of a shorebird is "open space." "Open," in landscape terms, means "without significant canopy cover (plants blocking the sky above)." A few shorebird species live or roost in trees or wooded areas, but in general they are adapted to live on sandy or rocky shores and open grassy areas. For adult shorebirds, "shelter" is provided more by flocks than by habitat. Individuals in a flock of roosting shorebirds take shelter from the wind behind each other. The bird at the front of the flock that faces the wind will eventually hop to the back of the flock, forcing another to take its turn as windbreaker before it, too, hops to the leeward side. Watch for this when you observe a roosting flock on a windy beach!
Migratory shorebirds spend about two months each year nesting and raising their young in inland tundra, muskeg, or grasslands or on ocean, lake, or river beaches. They live for most of the rest of the year in generally more southern and coastal areas. In fact, because the nonbreeding season is so long, shorebirds are more physically adapted to those southern habitats where they spend most of their lives.
There is at least one more habitat, and often several more, that Arctic-nesting shorebirds are dependent on each year. Besides their breeding and nonbreeding habitats, shorebirds depend on the habitats where they stop to rest and feed during their migratory journey. These stop-over sites tend to be beaches and estuaries (the wetland area where a stream or river drains into the sea) that are relatively small in size. They are full of abundant food and may support a concentration of thousands or even millions of shorebirds every spring or fall (many shorebirds have migratory paths that differ in the fall and spring).
These migratory paths and stops have been used year after year for a very long time. When a large portion of a population of birds are all present at one time on one site, storms or oil spills could kill or injure many individuals and, therefore, have a significant effect on population size.
Many migrating shorebirds are not flexible enough, nor have the time, to find alternatives to the preferred habitat of their traditional stopover or nesting sites.
Significance of Wetland Habitat for Shorebirds
Although a given shorebird species may nest on the grassy tundra, stop on migration at ocean beaches and estuaries, and spend its winter on distant mudflats or beaches, all of these different habitats have something in common. Most of the habitats that shorebirds depend on are wetlands. As we shall see, there are many types of wetlands. Because they have shallow water (allowing plant growth, penetration of light and warmth, and buoyancy and nourishment for developing young), most wetlands are important sources of food and shelter for many organisms. In other words, they provide essential habitat.
Many shorebirds, like Western Sandpipers, nest on upland tundra in the Arctic. This relatively dry type of tundra is still formed on permafrost, which does not allow precipitation or melting snow to drain, and pools of water abound. Migration and wintering habitats tend to be wetter than breeding habitats.
Shorebirds and Humans share an Important Habitat
Wetlands are attractive habitats for humans as well. Humans use wetlands as a source of water for power, crop irrigation, transportation, drinking, and recreation. We find these areas attractive for housing and desirable as ports. Highway bridges span them, and water and sewer plants are built near them. Runoff water from streets and polluted ditches, and sometimes even sewage, empties into them. Great cities like San Francisco, Seattle, and Anchorage have grown up in what were formerly vast wetlands. Non?native ("exotic") species are being introduced into wetlands from such sources as the ballast water of ships, and sometimes these introduced species can outcompete native ones and seriously alter the structure of the wetland.
Unfortunately, the amount of wetland habitat on our planet is limited. Also, most of our use of these fragile wetlands has been permanently destructive. Because wetlands receive runoff water from the surrounding landscape, they receive agricultural chemicals that run off in this water as well. Does water containing the oil from cars and the soap from car washings on your street make its way to a storm drain that empties into local wetlands? Wetlands are being drained and polluted. Our port cities and coastal wetlands face the dangers of accidental oil spills.
As wetland habitat shrinks, shorebirds and countless other animals and plants lose the habitats they rely on. We humans lose wetland habitats important to us for reasons as diverse as clean water, fish, flood control, and tranquil beauty. Is it possible that humans and shorebirds can survive, even thrive, together using the same wetlands? One thing is certain, the more we learn about the components that make up the habitats of our earth, and the intricate interactions between all the organisms living here, the better our chances of making the best decisions for the future.
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