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Discovering California Least Tern Migration Patterns |
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The California least tern (Sterna antillarum browni, hereafter “CALT”) was listed as endangered by the federal government in 1970. The entire species was listed in 1985. A great deal of effort and funding has gone into protecting CALT on breeding habitat, mainly within the southern California region. The primary work has been done by the Department of Navy (DoN) in San Diego and at Marine Corps Base Camp Pendleton. More protected habitat is located at Vandenberg Air Force Base and other sites, e.g. Port of San Diego lands. DoD spends, over a period of several years, millions of dollars managing the northern breeding habitats of this endangered species. Unfortunately, DoD, U.S. Fish and Wildlife Service (USFWS) and other California managers have little information about habitat conditions and threats south of the Mexican border. CALT spend approximately 7-8 months each year in these southern areas that directly affect the long-term success of DoD efforts to effectively manage this species to recover
CALT and their wintering habitats south of the United States border are partially known, due to banding and limited observations by researchers in California. But very little is known of the migration habitat used by this species as it travels between the tropics and Baja California. The Department of Defense (DoD) elected in 2003 to fund a Legacy study of the migration patterns and wintering habitats of this species of neo-tropical migrant. The first year of this study focused on two primary and two secondary goals. Primary goals are: 1) developing and upgrading information on breeding populations of CALT in Baja California; and, 2) modeling the proposed radio-transmitting technology (crossband transponder system) on a surrogate, non-endangered species, as required by the USFWS, prior to its use on the endangered CALT. The secondary 2003 goals are: to investigate reports of resident and migratory populations of least terns along the mainland coast of southwestern Mexico; and, the initiation of an international monitoring network that will regularly provide data on the ecological welfare of CALT and their habitats.
The primary focus of Earthspan’s work toward this larger project involved the tagging of Forster’s Terns to develop methods that could later be used on CALT. The overall goal of tagging Forster’s terns (a surrogate tern species used to model technology) with a simulated crossband transponder tag (a modified avian VHF transmitter) was to determine the efficacy of using this type of technology. The effort had the following specific objectives:
1. Determine
effective tern capture methodologies;
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