Please use this identifier to cite or link to this item:
Title: 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
Authors: Lott, Casey A.
Keywords: Bird surveys
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical Report (Engineer Research and Development Center (U.S.)) ; no. ERDC/EL TR-06-13
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. Lesser numbers of terns were counted on the Ohio River system (1.0 percent), the Trinity River system in Texas (1.0 percent), the Rio Grande/Pecos River system in New Mexico and Texas (0.8 percent), the Wabash River System (0.6 percent), two reservoirs in East Texas (0.3 percent), and the Kansas River system (0.3 percent). A majority of adult terns were counted on rivers (89.9 percent), with much smaller numbers at sand pits (3.6 percent), reservoirs (2.5 percent), salt flats (2.3 percent), industrial sites (1.4 percent), and rooftops (0.3 percent). This report discusses the results of the 2005 survey at three different spatial scales: 1) the entire breeding range for ILT and adjacent breeding populations on the Gulf Coast; 2) regional analyses by major river systems; and 3) individual survey segments (some of which have been combined into geographic segments comprised of more than 1 similar survey segment). Results of the 2005 survey are also compared with historic survey data from 1986 through 2004. The value of historic data for local, regional, and range-wide analyses of population trends is evaluated in the context of this first complete picture of the breeding distribution of ILT. Recommendations are made to 1) increase annual survey coverage for ILT to include several important breeding areas documented in this report that do not receive regular monitoring attention; 2) conduct additional large-scale surveys (such as the 2005 survey) during a standard survey window for long-term analyses of range-wide population trends; 3) conduct double-sampling to calculate detection ratios that will describe relative bias among survey segments with different survey methods; allowing unbiased estimation of population size and trend; and 4) improve long-term data storage for ILT count data through the development of a centralized data management system. The 2005 range-wide survey was a large collaborative effort that represents a major step forward toward developing the framework for a range-wide ILT monitoring program.
Description: Technical Report
Gov't Doc #: ERDC/EL TR-06-13
Rights: Approved for Public Release; Distribution is Unlimited
Size: 99 pages / 1.900 Mb
Types of Materials: PDF
Appears in Collections:Technical Report
Technical Report

Files in This Item:
File Description SizeFormat 
EL-TR-06-13.pdf1.95 MBAdobe PDFThumbnail