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    Interior Least Tern

    Nesting Interior Least Tern
    US Fish and Wildlife Service

Standardizing and Coordinating Range-wide Monitoring of the Interior Least Tern and its Habitat in a Metapopulation Context

Formal Title: Standardizing and Coordinating Range-wide Monitoring of the Interior Least Tern and its Habitat in a Metapopulation Context

Research Focus: bird monitoring, endangered species

Conservation & Management Challenges:

The Gulf Coastal Plains and Ozarks Landscape Conservation Cooperative partnered with the Great Plains, Plains and Prairie Potholes, Gulf Coast Prairie, and Eastern Tallgrass Prairie and Big Rivers Landscape Conservation Cooperatives, as well as the US Army Corps of Engineers, US Fish and Wildlife Service, US Geological Survey, and American Bird Conservancy to develop standardized range-wide monitoring protocols for both the Interior Least Tern (ILT) and its habitat, one of three requirements for delisting. Anticipated outcomes include the ability to assess population trends of the ILT and other river-dependent species, and to monitor species responses to habitat management. 


Research Overview:

Least Terns (Sternula antillarum) are colonial, fish-eating birds that nest on open, sandy habitats along rivers and coasts (Thompson et al. 1997), as well as on suitable anthropogenic habitats such as reservoirs and industrial sites. The “interior” populations of Least Terns (ILT) occur along large rivers in the central US, especially the Mississippi River and its major tributaries. In 1985, the ILT was listed as endangered under the Endangered Species Act (ESA) due to concerns that management of large rivers had led to population declines. 

The breeding ecology of the ILT has been discussed by the USFWS (1985, 1990), Kirsch and Sidle (1999), Lott et al. (2013), and references therein.

A substantial effort has been made in recent decades to survey ILTs. The USFWS  (2013) recently analyzed these data and threats to the ILT and found that the population had increased broadly across its range and that threats had diminished. They therefore concluded that the ILT is recovered and thus no longer needs protection under the ESA (USFWS 2013). The USFWS therefore identified development of a statistically valid post-delisting population trend monitoring strategy as a needed future action and noted that a monitoring plan would be described in any proposed rule to delist the species. This report describes one approach for a range-wide monitoring program.


Partners: US Army Corps of Engineers - Engineer Research and Development Center Environmental Laboratory; US Fish and Wildlife Service - Mississippi Ecological Services Field Office; US Geological Survey - Columbia Environmental Research Center; American Bird Conservancy


This project describes a cost-effective method for monitoring population trends for the federally endangered Interior Least Tern (ILT) throughout its range to be implemented once the tern is delisted. Current methods of counting adult ILT at colonies are shown to produce unreliable results. The researchers recommend 2 simple methods to improve reliability of ILT counts at colonies: 1) standardized double observer methods at colonies with <50 adults and 2) intensive surveys (described herein) at larger colonies. They propose that one-third of the non-excluded sampling areas be surveyed each year using a stratified random sampling plan. Based on simulations using historic counts, they estimate that this plan (1) will have a coefficient of variation (CV) of approximately 0.11 for estimates of the mean number of ILT at colonies, (2) will have nearly 100% power to detect a 50% decline occurring in 21 years or less and (3) will reduce costs of the current ILT surveys by more than 50%.


View of download the final ILT monitoring plan



This 2-year project was initiated in 2013 and the monitoring portion was completed in 2015. 


Principal Investigators: Casey A. Lott, American Bird Conservancy, email: (corresponding author); Jonathan Bart, Research Biologist, Jon Bart Consulting;; Richard A. Fischer, U.S. Army Corps of Engineers, Paul D. Hartfield, US Fish and Wildlife Service.  Project lead for the GCPO LCC: John Tirpak; US Fish and Wildlife Service, Gulf Restoration Program,  

Landscape Conservation Cooperative Point-of-Contact: Bill Bartush, Gulf Coast Prairie LCC, National Wetlands Research Center, 700 Cajundome Boulevard, Lafayette, LA 70506 

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