Greater Yellowlegs (Tringa melanoleuca) is a migratory shorebird that occurs throughout the Western Hemisphere, from southernmost South America to Alaska and the boreal forests of Canada. While most know them as a species that occurs in small groups in freshwater or brackish wetlands during winter and migration, those who have visited the boreal forest in summer may envision a Greater Yellowlegs scolding them from the tops of spruce trees to protect their ground nest, possibly at the base of that same spruce!
One of the chief challenges of STEM maps to date has been to model the range and movements of waterbirds in addition to landbirds. Thanks to recent advancements in the models, Greater Yellowlegs is one of a suite of shorebirds now being modeled from eBird data.
Greater Yellowlegs is one of the more widespread shorebird species and, along with Sanderling, it may have one of the most extensive winter ranges. It is one of the shorebirds most likely to be found of Christmas Bird Counts in the United States, with regular wintering as far north as Massachusetts and Maine on the East coast and British Columbia on the West coast. Although most winter in coastal estuaries, in warmer regions they can be quite common at inland marshes and freshwater wetlands. Even small water bodies may host a Greater Yellowlegs: often it will be the only shorebird species at a small inland pond.
They occur throughout South America in winter, more commonly on the coasts, as far south as central Argentina and the southern portions of Chile. As seen on the map, the pampas–extensive seasonally wet grasslands south and west of Buenos Aires–is a really important wintering area for this species in Argentina. Unfortunately one of the areas with large concentrations of the species is northeastern South America, where thousands spend the winter (and hundreds oversummer), especially in the Brazilian states of Pará, Maranhão, and Amapá as well as French Guiana. STEM models don’t have enough data to work with to make predictions in this area; these areas badly need more eBird data so that we can produce more accurate models in these regions. Enter your records please if you have them!
Greater Yellowlegs are one of the earlier spring migrants, with early hints of northward movement visible along the Mississippi River Valley in the last week of February. During March they stream northward, showing up in coastal areas where they did not winter as well as inland marshes and pond edges as winter frost begins to lose its grip. A wet flooded field with puddles can be perfect habitat and full of yellowlegs.
The smaller cousin of Greater Yellowlegs, the Lesser Yellowlegs (Tringa flavipes) often occurs together in the same areas but tends to be a later migrant by two weeks or more. This migration timing can be a good aid to identification in spring.
Greater Yellowlegs is a forest bird in summer, occurring in bogs, muskeg, and clearings in spruce forest. They aggressively guard their territories with their loud calls. As with many species of central and northern Canada, eBird data are sparse so the STEM models have less information to work from, which is apparent from the fairly distinct “no prediction” edge to the range in the north.
Even though the model limits itself from making predictions far to the north, the range shown is quite accurate, showing the main breeding area in the northern Prairie Provinces (Manitoba, Saskatchewan, and Alberta) extending east to northern Ontario, Quebec, and Labrador and west to parts of Alaska. It does not breed in the mountains much, so British Columbia is relatively devoid of yellowlegs.
As with many shorebirds, a number of birds (especially immatures) oversummer on the winter range, and this is evident on the animation and accounts for the obvious signal along the coasts of southern Brazil, Uruguay, and Argentina during June. Some of these oversummering birds may have significant parasite loads that prevent migration: see the BNA account for more information on this.
Fall migration begins very early for Greater Yellowlegs, with the first southbound birds arriving in late June (note the 27 June map, which shows obvious arrival in the Lower 48 United States). They also have one of the longest migration windows of any American bird, as migrants can be found anytime from late June to mid-November. As with all shorebirds, the southward migration of adults precedes the migration of juveniles. In the field, you’ll see the southward migration of adults peaking late June to mid-September and juveniles from mid-August to mid-November.
Although the fall movement overlaps broadly with Lesser Yellowlegs, the migration timing still differs, with Greater Yellowlegs still on the move into November while most Lessers have reached their wintering range by late October.
To learn more about the life history of Greater Yellowlegs, please consider a subscription to Birds of North America (just $42/year), where experts in the species have written a full-length species account covering all aspects of the species biology, from migration to diet to conservation status.