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GAP Analysis Predicted Distribution Map

Caspian Tern (Sterna caspia)

Species Code: STCA

This is an "at risk" species

Click to enlarge Range map

= Core Habitat
= Marginal Habitat

Breeding Range Map
The green area shows the predicted habitats for breeding only. The habitats were identified using 1991 satellite imagery, Breeding Bird Atlas (BBA), other datasets and experts throughout the state, as part of the Washington Gap Analysis Project. Habitats used during non-breeding months and migratory rest-stops were not mapped.

Metadata (Data about data or how the map was made)

Click to enlarge distribution map

Other maps & Information:
  • Breeding Bird Atlas
  • NatureMapping observations
    during breeding season
  • NatureMapping observations
    throughout the year

This species primarily occurs on freshwater bodies in eastern Washington, nesting on sandy islands. They are locally common in Grant, Benton, Adams, Franklin, and Walla Walla Counties around Potholes Reservoir, Moses Lake, Winchester Wasteway, Crab Creek, Frenchman Hills Wasteway, Priest Rapids, Sprague Lake, Lake Lenore, Soap Lake, and Columbia National Wildlife Refuge. They were locally common in western Washington until 1995 at Everett, in Snohomish County, Grays Harbor, and Willapa Bay in Pacific County.

The core areas of use were the Central Arid Steppe, Canyon Grasslands, Big Sage/Fescue, and Three-tip Sage zones, and very locally in the Puget Sound Douglas-fir and Sitka Spruce zones. Good habitats in the east-side zones were fresh water/wetlands. Good habitats in the west-side zones were estuarine and coastal habitats.

This species has expanded its western Washington breeding range tremendously in recent decades, but current events may have caused these colonies to be extirpated. Large colonies in western Washington formerly established at the Everett Navy base include Jetty Island in Everett, which is being managed to provide suitable tern habitat (but unsuccessful as of this writing). Their numbers typically fluctuate year to year, and changes in plant colonies can displace colonies after a few years. In Grays Harbor, population oscillations were attributed to changes in island conditions due to erosion and competition from gulls. The coastal colonies utilize sand and spoil islands, which support the very sparse vegetation this species prefers. The eastern Washington colonies were established in the 1930s, and the Grays Harbor colony in 1957. Western Washington breeding birds have come from coastal California and western Mexico, indicating a southern migration and wintering route along the Pacific Ocean coast.

Translated from the Washington Gap Analysis Bird Volume by Uchenna Bright
Text edited by Gussie Litwer
Webpage designed by Dave Lester