A large shorebird, common on its northern prairie breeding grounds and in large wintering flocks in southern California and western Mexico, the Marbled Godwit breeds in the grasslands of the northern United States and southern Canada, with small isolated nesting populations in southwestern James Bay and Alaska (Figure 1).
The prairie breeding and short migrations of most Marbled Godwits contrast greatly with the long Arctic to southern South America migration of Hudsonian Godwits (Limosa haemastica). Uncommonly for shorebirds, both species sometimes forage almost exclusively on plant tubers during migration. Breeding behavior of the two species appears (at least superficially) similar, although that of Hudsonian Godwits in particular is little known.
Although the Marbled Godwit is a fairly common shorebird with easily accessible breeding populations, its ecology is little known. Only recently has the breeding and population biology of this species been studied in detail. Nests are not easily found, as these birds do not readily flush from eggs. (Incubating adults can sometimes be picked up from the nest.) Both parents share in incubation and brood care. The Marbled Godwit is long-lived and has a monogamous, conservative breeding system, nesting in fairly low densities throughout its range. Numbers appear to have increased slightly in some regions since the early twentieth century, when hunting of this species was banned. Probably because large portions of its former breeding habitats are now cropland, it has not increased in numbers to repopulate its former breeding range.
Most studies of Marbled Godwits have involved winter foraging behavior and habitat choice in California ( Luther 1968 , Gerstenberg 1972 , Kelly and Cogswell 1979 , Dodd and Colwell 1996 , Colwell and Dodd 1997 ). Similar studies of diet and foraging behavior during migration elsewhere are few ( Wishart and Sealy 1980 , Alexander et al. 1996 ), while considerable work on internal parasites has been carried out by Wong and Anderson ( Wong and Anderson 1991a , Wong and Anderson 1996 ). Key studies during the breeding season include Nowicki ( Nowicki 1973 ), adding considerably to our knowledge of godwit breeding behavior; Ryan ( Ryan 1982 , Ryan et al. 1984 ), examining breeding habitat; and Mehall-Niswander ( Mehall-Niswander 1997 ), describing behavior and habitat selection in the Alaskan population. Population biology has been examined recently (CLG-T).