The Winter Distribution of the Western Gull-billed Tern (Gelochelidon nilotica vanrossemi). Molina, K. C., Garrett, K. L., Larson, K. W., & Craig, D. P. Western Birds, 40(1):2–20, 2009. 00000
The Winter Distribution of the Western Gull-billed Tern (Gelochelidon nilotica vanrossemi) [link]Paper  doi  abstract   bibtex   
We surveyed 73 sites along the Gulf of California and Pacific coasts of mainland Mexico during five nonbreeding seasons from December 1999 to January 2007 to clarify the winter status and distribution of the western North American subspecies of the Gull-billed Tern (Gelochelidon nilotica vanrossemi), a taxon of conservation concern. We located birds at 44 of the 73 sites, (60%) with the largest numbers found around coastal lagoons with extensive tidal flats in southern Sonora, Sinaloa, and extreme northern Nayarit. Local concentrations were also noted at other sites from the Colorado River delta of extreme northwestern Sonora south to Guerrero. Resightings of birds banded as chicks at California breeding colonies establish the first evidence of connectivity to specific wintering sites in Mexico as far south as southern Sonora and possibly into Nayarit. The Gull-billed Tern (Gelochelidon nilotica) is widespread in temperate, subtropical, and tropical regions of the Old and New Worlds, but many populations, particularly those in North America, appear to be declining (Parnell et al. 1995, Molina and Erwin 2006). The western North American subspecies (G. n. vanrossemi, the Western Gull-billed Tern) of southern California and western Mexico breeds at few known colonies, and its seasonal movements are poorly understood. The limited range and low population size of this subspecies (about 250 breeding pairs in the United States and perhaps as few as 600 pairs throughout its range in western Mexico; Molina and Erwin 2006, Palacios and Mellink 2007) has led to its listing as a species of special concern in California (Remsen 1978, Molina 2008) and a national bird of conservation concern (USDI 2002). Gull-billed Terns are less dependent on marine and other aquatic habitats than are many other species of terns, and they commonly forage over a variety of terrestrial habitats. Their broad diet includes a variety of insects, marine invertebrates, reptiles, amphibians, small fish, and the small chicks of birds; as opportunistic feeders they often exploit ephemerally abundant populations of prey such as crickets and weevils (Molina 2008). These terns frequently forage singly or in groups of two or three individuals (Molina and Marschalek 2003). Nearly all of our knowledge of Gull-billed Tern ecology results from studies conducted during the breeding season (Parnell et al. 1995). Conservation efforts directed toward migratory species, however, require an understanding of distribution and ecology throughout the year (Coulter and Frederick 1997, Kushlan et al. 2002, Martin et al. 2007). The winter range of the Western Gull-billed Tern has been outlined in the literature only in general terms (Howell and Webb 1995, Parnell et al. 1995), with some treatments (e.g., Hellmayr and Conover 1948, American Ornithologists' Union 1957) suggesting this subspecies winters south to Ecuador. Breeding populations in California (Salton Sea and south San Diego Bay) withdraw southward (Patten et al. 2003, Unitt 2004, Molina and Erwin 2006). Although Molina and Erwin (2006) presented more detail on winter distribution and included a brief analysis of the limited Christmas Bird Count (CBC) data available from Mexico, the extent of the subspecies' winter range in Mexico and the areas and habitats supporting important concentrations have not been described. Here we report on the results of surveys for Gull-billed Terns in western Mexico conducted during five winters between 1999 and 2007. Our objectives are to determine geographical areas and habitats of importance to this subspecies during the winter period and, secondarily, to link California-breeding Gull-billed Terns to specific sites used in the nonbreeding season. We also review other published and unpublished information on the winter range of vanrossemi to amplify our survey results.
@article{molina_winter_2009,
	title = {The {Winter} {Distribution} of the {Western} {Gull}-billed {Tern} ({Gelochelidon} nilotica vanrossemi)},
	volume = {40},
	issn = {0160-1121},
	url = {http://dx.doi.org/10.1675/1524-4695(2006)29[271:TDACSO]2.0.CO;2},
	doi = {10.1675/1524-4695(2006)29[271:TDACSO]2.0.CO;2},
	abstract = {We surveyed 73 sites along the Gulf of California and Pacific coasts of mainland Mexico during five nonbreeding seasons from December 1999 to January 2007 to clarify the winter status and distribution of the western North American subspecies of the Gull-billed Tern (Gelochelidon nilotica vanrossemi), a taxon of conservation concern. We located birds at 44 of the 73 sites, (60\%) with the largest numbers found around coastal lagoons with extensive tidal flats in southern Sonora, Sinaloa, and extreme northern Nayarit. Local concentrations were also noted at other sites from the Colorado River delta of extreme northwestern Sonora south to Guerrero. Resightings of birds banded as chicks at California breeding colonies establish the first evidence of connectivity to specific wintering sites in Mexico as far south as southern Sonora and possibly into Nayarit.

The Gull-billed Tern (Gelochelidon nilotica) is widespread in temperate, subtropical, and tropical regions of the Old and New Worlds, but many populations, particularly those in North America, appear to be declining (Parnell et al. 1995, Molina and Erwin 2006). The western North American subspecies (G. n. vanrossemi, the Western Gull-billed Tern) of southern California and western Mexico breeds at few known colonies, and its seasonal movements are poorly understood. The limited range and low population size of this subspecies (about 250 breeding pairs in the United States and perhaps as few as 600 pairs throughout its range in western Mexico; Molina and Erwin 2006, Palacios and Mellink 2007) has led to its listing as a species of special concern in California (Remsen 1978, Molina 2008) and a national bird of conservation concern (USDI 2002).

Gull-billed Terns are less dependent on marine and other aquatic habitats than are many other species of terns, and they commonly forage over a variety of terrestrial habitats. Their broad diet includes a variety of insects, marine invertebrates, reptiles, amphibians, small fish, and the small chicks of birds; as opportunistic feeders they often exploit ephemerally abundant populations of prey such as crickets and weevils (Molina 2008). These terns frequently forage singly or in groups of two or three individuals (Molina and Marschalek 2003). Nearly all of our knowledge of Gull-billed Tern ecology results from studies conducted during the breeding season (Parnell et al. 1995). Conservation efforts directed toward migratory species, however, require an understanding of distribution and ecology throughout the year (Coulter and Frederick 1997, Kushlan et al. 2002, Martin et al. 2007).

The winter range of the Western Gull-billed Tern has been outlined in the literature only in general terms (Howell and Webb 1995, Parnell et al. 1995), with some treatments (e.g., Hellmayr and Conover 1948, American Ornithologists' Union 1957) suggesting this subspecies winters south to Ecuador. Breeding populations in California (Salton Sea and south San Diego Bay) withdraw southward (Patten et al. 2003, Unitt 2004, Molina and Erwin 2006). Although Molina and Erwin (2006) presented more detail on winter distribution and included a brief analysis of the limited Christmas Bird Count (CBC) data available from Mexico, the extent of the subspecies' winter range in Mexico and the areas and habitats supporting important concentrations have not been described. Here we report on the results of surveys for Gull-billed Terns in western Mexico conducted during five winters between 1999 and 2007. Our objectives are to determine geographical areas and habitats of importance to this subspecies during the winter period and, secondarily, to link California-breeding Gull-billed Terns to specific sites used in the nonbreeding season. We also review other published and unpublished information on the winter range of vanrossemi to amplify our survey results.},
	number = {1},
	journal = {Western Birds},
	author = {Molina, Kathy C. and Garrett, Kimball L. and Larson, Keith W. and Craig, David P.},
	year = {2009},
	note = {00000},
	keywords = {\#nosource},
	pages = {2--20},
}
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