Red Knot Habitat Model
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Red Knot, Calidris canutus; American subspecies: C. c. rufa
Use of Study Area Resources:
Migration (also occasional wintering occurrences in Massachusetts); use coastal portions of the study area. Red knots breed in Greenland, on Canadian islands from Victoria to Ellesmere, Alaska, and Siberia, then make some of the longest migrations known, to winter in South Africa, Argentina, and New Zealand (Harrington 1983). May winter from southern Massachusetts south to South America (Johnsgard 1981).
Red knots are spectacular long-distance migrant shorebirds that breed in high arctic tundra and spend the non-breeding season much further south in temperate and tropical coastal areas, which include the northern coast of Brazil and the east coast of Argentina (Gonzalez 1996). While migrating they stop and feed actively at intermediate points, known as staging areas. Such areas offer abundant food resources, which enables shorebirds to gain mass rapidly, then continue their migration (Botton et al. 1994). Staging stops include coastal beaches, sandbars, mudflats, salt marshes, river deltas, and rock shelves (DeGraaf and Rappole 1995, Hayman et al. 1986, Gonzalez et al. 1996, Botton et al. 1994). Knots rarely occur inland from the coast during migration (Hayman et al. 1986).
Feeding is done by probing wet substrate with their long bill. Botton et al. (1994) note that red knots on the mid-Atlantic coast feed on horseshoe crab eggs, the most abundant food item on (the) beaches at a time when few other macroinvertebrates are available. Gonzalez et al. (1996) described red knots in Argentina feeding on a rocky flat on small mussels which were abundant, easily detected, easily detached, and had short handling times of 1-2 s. There knots roosted in dense flocks on the adjacent beach at high tide, dispersing in groups as the intertidal zone was exposed, and following the receding water line. Although knots will pull mussel spat off rocky substrates, they prefer to forage on exposed old salt marsh peat, from which they more easily remove spat (Harrington 1983). The red knot diet includes mollusks, snails, small fishes, horseshoe crab eggs, marine worms, insects- especially flies and beetles, seeds and vegetation (Sperry 1940 in Terres 1995).
The habitat model relied on abundance/occurrence information from a Maine Department of Inland Fisheries and Wildlife (MDIFW) shorebird coverage, and the Manomet Bird Observatory's International Shorebird Survey (ISS) database for Massachusetts and New Hampshire. The occurrence information was used to select the general localities used by the species. Environmental data sets (bathymetry and wetland cover type) were used to select areas within those localities likely to have been occupied. The ISS data specified the observation locations only to the nearest, so all suitable cover types (see table, below) within a 1 km radius of those points were regarded as having the level of use indicated at the observation point.
|Cover Types||Cover Suitability
(0 - 1 scale)
|Upland deciduous forest|
|Upland coniferous forest|
|Upland mixed forest|
|PEM, L2EM||Lake/pond, emergent vegetation|
|PFOcon||Palustrine forest, conifer|
|PFOdec||Palustrine forest, deciduous|
|PSSdec||Palustrine scrub shrub, deciduous|
|PSScon||Palustrine scrub shrub, conifer|
|PAB, L2AB||Lake/pond, aquatic vegetation|
|L1UB, PUB||Lake/pond, unconsolidated bottom|
|L2US||Lake, unconsolidated shore|
|L2RS||Lake, rocky shore|
|R1UB||Riverine subtidal unconsolidated|
|E1AB||Estuarine subtidal vegetated|
|E1UB||Estuarine subtidal unconsolidated bottom|
|E2AB||Estuarine intertidal algae|
|E2EM||Estuarine intertidal emergent||0.5|
|E2RS, R1RS||Estuarine, tidal river rocky shore||0.5|
|E2SS||Estuarine intertidal shrub|
|E2US, R1US||Estuarine, riverine intertidal unconsolidated shore||1.0|
|M1AB||Marine subtidal vegetated|
|M1UB||Marine subtidal unconsolidated bottom|
|M2AB||Marine intertidal algae|
|M2RS||Marine intertidal rocky shore||0.5|
|M2US||Marine intertidal unconsolidated shore||1.0|
Habitat Suitability Scoring: Sites with red knot occurrences and having any of the suitable landcover types (see table) were scored according to level of use. If a site had 5 or more birds observed at any time, the suitability index = 1.0; else, if any birds were present the suitability index = 0.5. This value was multiplied by the landcover score.
Suitable cover types outside of the observation/occurrence polygons were scored as potential foraging habitats; unconsolidated sediment cover types were rescored 0.2, rocky and marsh types rescored 0.1.
Botton, M.L., R.E. Loveland and T.R. Jacobsen. 1994. Site selection by migratory shorebirds in Delaware Bay, and its relationship to beach characteristics and abundance of horseshoe crab (Limulus polyphemus) eggs. The Auk 111(3): 605-616.
DeGraaf, R.M. and J.H. Rappole. 1995. Neotropical Migratory Birds: Natural History, Distribution and Population Change. Comstock Publishing Associates, Ithaca, NY. 1995. 676 pp.
Gonzalez, P.M., T. Piersma and Y. Verkuil. 1996. Food, feeding, and refuelling of red knots during northward migration at San Antonio Oeste, Rio Negro, Argentina. J. Field Ornithol. 67(4): 575-591.
Harrington, B. 1983. The migration of the red knot. Oceanus 26(1):4-48.
Hayman, P., J. Marchant and T. Prater. 1986. Shorebirds: an Identification Guide to the Waders of the World. Houghton Mifflin Co., Boston, MA. 412 pp.
Johnsgard, P.A. 1981. The Plovers, Sandpipers and Snipes of the World. University of Nebraska Press. Lincoln, NE. 493 pp.
Terres, J.K. 1995. The Audubon Society Encyclopedia of North American Birds. Wings Books, Avenel, NJ.