Meet the Red Knot
Species: Red Knot (Calidris canutus)
Status in the Northwest:
• Washington: no special conservation status, but identified in Washington State Wildlife Action Plan as a Species of Greatest Conservation Need (WDFW 2015).
• Oregon: no special conservation status.
• USFWS: C.c. roselaari is a Bird of Conservation Concern in Bird Conservation Region 5 (USFWS 2008).
• Recent analyses indicate the presence of two genetically distinct populations of Red Knots within the Pacific Flyway, in contrast to the previously recognized single population of C. c. roselaari. Subspecies status of the two populations has not been formally established.
Range:
Red Knots of the North American Pacific Flyway overwinter from central coastal California to northwestern coastal Mexico, with the vast majority of the population found in Mexico; they breed at Wrangel Island, Russia (one genetic population) and in northwestern Alaska (another genetic population). Northbound migrants stop almost exclusively at Grays Harbor and Willapa Bay, Washington, and at the Copper River and Yukon-Kuskokwim River deltas, Alaska, and southbound migrants stop at the Yukon-Kuskokwim River Delta before flying directly to overwintering areas. First-year birds stay in Mexico rather than migrating north. Away from this small number of key locations, Red Knots occur in very small numbers; for example, they appear to almost completely bypass Oregon and British Columbia during migration.
Ongoing banding and satellite telemetry investigations have confirmed these findings and produced new information about a potentially important stopover or staging site in northern Mexico. Although both populations migrate through Washington and use the same habitats here, we currently lack information on whether they co-occur at overwintering sites. To better understand the annual ecology and behavior of Red Knots we work with a network of dedicated and enthusiastic researchers from Russia to Mexico, regularly communicating, collaborating, and sharing data on movements of knots.
Habitat:
Red Knots in Washington use estuarine mudflats that vary from silt to sand-silt. High tide roost sites used by most knots are typically isolated sand shoals in Grays Harbor and Willapa Bay, although small numbers of knots occasionally roost on outer sand beaches.
Conservation Issues:
Limited information suggests the population of Red Knots on the Pacific Flyway has declined in recent decades, but the cause of the suspected decline is unknown. The subspecies found on the Atlantic coast (C. c. rufa) is listed under the Endangered Species Act, and one factor in its listing was a de-coupling of resource availability during migration as a result of climate change. In Washington, primary foraging areas in Willapa Bay were largely covered by invasive Spartina (cordgrass) in the 1990s and this may have reduced the carrying capacity of the site for about one decade until the cordgrass was removed. Parts of the overwintering range in coastal mainland Mexico have been altered by construction and management of shrimp farms. The relevance of these potential impact factors remains unknown.
The population of C. c. roselaari that migrates through coastal Washington was recently estimated at 21,800 individuals, making it the smallest of six Red Knot populations globally and the least abundant Calidrid that migrates primarily along the Pacific Flyway between Mexico and Arctic or near-Arctic breeding areas. Given the existence of two distinct genetic populations in the flyway, each of these populations will be smaller than the current estimate of 21,800 birds.
Many shorebird species are associated with freshwater or freshwater-marine estuaries in the Pacific Northwest. Most of these species are broadly distributed habitat generalists, such that the presence of high-functioning mudflats will attract and be used by multiple species. For this reason, conservation of shorebird habitat will benefit numerous species at the site and regional level. Although Red Knots use silty and sandy mudflats, they are not generally distributed. The entire flyway population is extremely localized in distribution during spring migration (Grays Harbor and Willapa Bay, Washington) between Mexico and Alaska. Within these estuaries, the knots prefer and are most abundant in the northern half of Grays Harbor and the extreme northern end of Willapa Bay, possibly in response to the availability of their bivalve prey. Consequently, this high association with specific areas and food conditions means that general conservation initiatives for shorebirds would be expected to benefit Red Knots only if the areas used by knots were to be included.
Numerous threat factors have been identified for shorebirds along the Pacific Flyway of the Americas, and some appear relevant to Red Knots in Washington. Invasive Spartina has been eradicated, but maintenance control is ongoing; re-establishment of invasive cordgrass on the mudflats would reduce the area of foraging habitat, so continuing the maintenance control is essential. In addition, Spartina traps sediments and sediment accumulation has been documented in areas of Willapa Bay where Spartina was removed, possibly making these areas less productive foraging habitat. An oil spill in either of the bays could directly impact knots or their prey. Climate change effects could include changes to the amount and distribution of appropriate foraging habitat; in both estuaries there is little room adjacent to the estuaries for mudflats to ‘migrate’ during sea level rise. Geochemical changes may also be occurring (e.g., ocean acidification could alter bivalve food resources). Lastly, we have no evidence that shellfish production impairs Red Knot population performance. However, shellfish production occurs in known knot foraging areas and may reduce the overall available foraging area.
Read more about estuary habitats, the threats they face, and the species that live there on the eBird Northwest Habitat Page.
Read more species articles on eBird Northwest here.
Figure 1. Connectivity of Red Knots between key sites along the Pacific Flyway. This map depicts direct linkages between sites, although the lines do not indicate actual flight routes. Indirect linkages also occur within the flyway, but are not shown (e.g., knots banded at Wrangel Island have been observed at Grays Harbor and Willapa Bay). Most linkages are supported by observations of many individually-identifiable knots (in some cases, hundreds of birds). Very small numbers of marked knots (e.g., 1-3) have been observed at several secondary sites (not shown) between the key sites on the map. Large aggregations of knots overwinter along the coastal area of northern mainland Mexico south to Las Garzas, but there have been no intensive efforts to observed marked knots in those areas; such information would likely add more direct linkages to the map. This map is based on banding/resighting and telemetry data through 2018. Map made by WDFW.
Figure 2. Map of the likely overwinter distribution of Pacific Flyway Red Knots in coastal Mexico (map from Carmona et al. 2013). Hundreds of Red Knots overwinter at San Francisco Bay, the greater San Diego area, and Salton Sea, California (not shown). The cluster of aggregation sites on the Baja Peninsula and the adjacent coastal area of mainland Mexico may represent much of the overwinter distribution of the two Pacific Flyway populations. These records were assembled from the literature and the eBird site in support of a summary presented in Carmona et al. (2013).
Additional Resources:
Bishop, M.A., J.B. Buchanan, B.J. McCaffery & J.A. Johnson. 2016. Spring stopover sites used by the Red Knot Calidris canutus roselaari in Alaska, USA: connectivity between the Copper River Delta and the Yukon-Kuskokwim River Delta. Wader Study 123: 143-152.
Buchanan, J.B. 2003. Spartina invasion of Pacific Coast estuaries in the United States: implications for shorebird conservation. Wader Study Group Bulletin 100: 47-49.
Buchanan, J.B., J.E. Lyons, L.J. Salzer, R. Carmona, N. Arce, G.J. Wiles, K. Brady, G.E. Hayes, S.M. Desimone, G. Schirato & W. Michaelis. 2012. Among-year site fidelity of Red Knots during migration in Washington. Journal of Field Ornithology 83: 282-289.
Buchanan, J.B., L.J. Salzer & V. Loverti. 2017. Between-year variation in the timing of peak passage of spring migrant Red Knots at Grays Harbor, Washington, USA. Wader Study 124: 238-240.
Buchanan, J.B., L.J. Salzer, G.J. Wiles, K. Brady, S.M. Desimone & W. Michaelis. 2011. An investigation of Red Knot Calidris canutus roselaari spring migration at Grays Harbor and Willapa Bay, Washington. Wader Study Group Bulletin 118: 97-104.
Carmona, R., N. Arce, V. Ayala, A. Hernández-Alvarez, J.B. Buchanan, L.J. Salzer, P.S. Tomkovich, J.A. Johnson, R.E. Gill, Jr., B. McCaffery & J. Lyons. 2013. Red Knot (Calidris canutus roselaari) migration connectivity, abundance and nonbreeding distribution along the Pacific coast of the Americas. Wader Study Group Bulletin 120: 168-180.
Chappell, C.B. 2005. Red Knot (Calidris canutus). In: Birds of Washington: status and distribution. T.R. Wahl, B. Tweit & S.G. Mlodinow (eds). Oregon State University Press, Corvallis, OR USA. pp. 152–153.
Lyons, J.E., W.L. Kendall, J.A. Royle, S.J. Converse, B.A. Andres & J.B. Buchanan. 2016. Population size and stopover duration estimation using mark-resight data and Bayesian analysis of a superpopulation model. Biometrics 72: 262-271.
Senner, S.E., B.A. Andres, and H.R. Gates. 2016. Pacific Americas shorebird conservation strategy. National Audubon Society, New York, NY, USA http://www.shorebirdplan.org
U.S. Fish and Wildlife Service. 2008. Birds of Conservation Concern 2008. United States Department of Interior, Fish and Wildlife Service, Division of Migratory Bird Management, Arlington, Virginia. 85 pp. https://www.fws.gov/birds/management/managed-species/birds-of-conservation-concern.php
U.S. Shorebird Conservation Plan Partnership. 2016. U.S. Shorebird Conservation Plan Partnership – 2016. http://www.shorebirdplan.org/science/assessment-conservation-status-shorebirds/
Washington Department of Fish and Wildlife. 2015. Washington’s State Wildlife Action Plan: 2015 Update. Washington Department of Fish and Wildlife, Olympia, Washington, USA. https://wdfw.wa.gov/species-habitats/at-risk/swap
Article written by Joseph Buchanan, WDFW