Estuaries

6 Jun 2019 By eBird Northwest Team

Available Languages

Bandon Marsh © Creative Commons Rick Obst

Pacific Northwest estuaries support millions of birds

Estuaries occur where freshwater systems connect and intermingle with the salt waters of the ocean. Estuaries are actually an ecosystem made up of numerous habitats, such as tidal mud flats, eelgrass beds¬ or saltwater marshes. Thanks to the mixing of nutrients from both land and sea, they are among the most biologically-rich ecosystems on Earth. Estuaries act as ecological buffers where sediment and excess nutrients or pollutants from the watershed are filtered before reaching marine waters, and the land is protected from the forces of wind and waves.

Whether from the invertebrates hidden in the mud, the biotic life associated with marsh plants, or the invertebrates and fish in the water column, estuaries provide an abundant food source for both migratory and resident birds. Millions of them¬ – particularly shorebirds and waterfowl – rely on the network of estuaries along the Pacific Flyway. While some species prefer certain estuaries – Brant, for example, specifically depend on eelgrass habitats within certain estuarine ecosystems – it is the collective network that supports species across their annual cycles and is so important to bird life in the Pacific Northwest.

Estuaries matter to all birds, but especially shorebirds and waterfowl species

All bird groups use the flywayʻs estuaries, but it is the shorebirds and waterfowl that show up in astounding numbers. Western Sandpipers, Dunlin and other shorebird species that breed in the far north stopover in Pacific Northwest estuaries by the tens or hundreds of thousands during spring migration.

It is estimated that 500,000 shorebird have visited Washington’s Grays Harbor during spring migration. Photo © Dan Dzurisin

Red Knots that breed in Alaska and Russia, and spend the winter further south along the flyway, rest and refuel in Grays Harbor and Willipa Bay before continuing north during spring migration. Many other shorebirds, such as the Snowy Plover, rely on estuaries and adjacent upland beaches for feeding, resting, and breeding.

The waterfowl numbers in Pacific Northwest estuaries, bays and deltas are equally impressive. The Fraser, Puget Sound and many other estaurine or delta habitats support Trumpter Swans, Snow Geese, Mallards, Northern Pintail, American Wigeons, Canada Geese, Harlequin Ducks, White-winged Scoters, Barrowʻs Goldeneye and additional waterfowl and seabird species. According to Ducks Unlimited, a million waterfowl have been counted in the Samish and Skagit River Delta areas. Raptors such as the Short-eared Owl, a common bird in steep decline, also benefit from the abundant food supplies in estuarine environments, as do other landbird and waterbird species.

Estuarine habitats also support numerous species of fish, including juvenile salmon as they migrate from fresh to salt water. These young fish get both food and shelter from estauries as they undergo major physiological changes. While they are in the estuaries, they become part of the complex food web, eating invertebrates and providing an abundant food source for larger fishes and birds.

Conservation Threats

The conservation threats to estuaries are diverse. Diffuse or concentrated pollutants from the watersheds – such as nutrient run-off, sewage, sediment, and pesticides – will degrade estuarine and marine waters. Invasive species pose threats to the integrity of estuarine habitats, and major pollution events such as oil spills pose direct threats to habitats in their path.

Development in the coastal zone, such as dredging and diking, may increase sedimentation and alter the specific habitats needed by plants and animals. Sea level rise and changing land and water temperatures are altering the biotic landscape for estuarine species. Sea level rise will present challenges to waterfowl, shorebirds, and all estuarine-dependent species, since their food sources are dependent upon salinity and water depth. Existing diking, development or other land uses near the estuaries may not allow for the inland migration of estuarine habitats with the rising seas.