First Range-wide Survey for the Endangered Interior Least Tern

Least Tern. Photo: USFWS

In 2005, ABC coordinated the first range-wide survey of the interior population of the Least Tern, providing the first complete picture of its numbers and distribution.

The Least Tern nests along both coastlines of the United States and Mexico, and on sandbars in large rivers, primarily within the Mississippi, Missouri, Platte, Arkansas, and Red River systems. In 1985, the "interior" Least Tern, (all Least Terns nesting more than 30 miles inland from the Gulf of Mexico) was federally listed as Endangered due to low numbers and concerns about habitat loss. At the time, survey coverage for interior Least Terns was incomplete and their range-wide distribution was poorly known. Survey coverage improved steadily following listing, though large portions of the range remained inadequately surveyed, and local monitoring efforts were rarely coordinated or analyzed at larger scales.

In April 2004, ABC and the U.S. Army Corps of Engineers brought together biologists from across the tern's entire range, resulting in the formation of the 'Interior Least Tern Working Group,' with the aim of improving monitoring and trend analysis.

Then, during the 2005 breeding season, ABC coordinated the first national survey of all known interior Least Tern nesting areas. The primary objectives of this survey were to provide a minimum count of the number of adult terns occurring in North America during the breeding season, document the distribution and abundance of nesting colonies, and describe the types of habitats that are being used for nesting.

Crews surveyed 4,515 river miles, over 14,000 acres of salt flats, 12 reservoirs, and 61 sand pits. A total of 17,871 terns were counted at a minimum of 487 different colonies. A majority of adult terns were counted on rivers (89.9%), with much smaller numbers at sand pits (3.7%), reservoirs (2.7%), salt flats (2.1%), industrial sites (1.5%), and roof-tops (0.3%). Just over 62% of all adults were counted on the Lower Mississippi River between Cape Girardeau, Missouri, and Baton Rouge, Louisiana.

More than 140 participants from a large number of agencies and organizations took part in this survey, which will provide the foundation for ongoing efforts to devise a range-wide monitoring plan.

Download the complete survey