Distribution and Abundance of the Interior Population of the Least Tern (Sternula Antillarum), 2005; A Review of the First Complete Range-Wide Survey in the Context of Historic and Ongoing Monitoring Efforts

Abstract

Abstract : The interior population of the Least Tern (Sternula antillarum) was added to the U.S. Fish and Wildlife Service (USFWS) list of threatened and endangered species in 1985 because of suspected low numbers and concerns about breeding season habitat loss or degradation on large interior rivers. Range-wide survey data were incomplete when Interior Least Terns (ILT) were originally listed. Although many ILT counts have been conducted over the past 20 years, regular survey coverage is still incomplete across the large breeding range of ILT, limiting the ability to assess the conservation status or trends for this population. During the last two weeks of June and the first week of July 2005, over 140 participants contributed to the first complete range-wide survey for ILT (see acknowledgments). The primary objectives of this survey were 1) to provide a minimum count of the number of adult ILT occurring in North America during the breeding season, 2) to document the range-wide distribution of nesting colonies, and 3) to describe the types of habitats that are being used for nesting. Survey crews covered ~4,700 river miles, 22 reservoirs, 62 sand pits, 12 industrial sites, 2 rooftop colonies, and over 16,000 acres of salt flats, counting a grand total of 17,591 ILT in association with 489 different colonies. Just over 62 percent of all adult ILT were counted on the Lower Mississippi River (10,960 birds on 770+ river miles). Four additional river systems accounted for 33.3 percent of the remaining ILT, with 11.6 percent on the Arkansas River system (including the Canadian and Cimarron Rivers and the Salt Fork of the Arkansas River), 10.4 percent on the Red River system, 6.9 percent on the Missouri River system, and 4.4 percent on the Platte River system.