Interior Least Tern (Sternula antillarum) breeding distribution and ecology: implications for population‐level studies and the evaluation of alternative management strategies on large, regulated rivers

• Published in: Ecology and evolution Vol. 3; no. 10; pp. 3613 - 3627
• Main Authors: Lott, Casey A., Wiley, Robert L., Fischer, Richard A., Hartfield, Paul D., Scott, J. Michael
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-09-2013; Blackwell Publishing Ltd
• Subjects: Anthropogenic factors; Bird populations; Birds; Breeding; Channels; Colonization; Dam engineering; Demographics; Dispersal; Dispersion; Ecological monitoring; ecological response to dams and flow alteration; Geophysics; Habitats; High flow; Historical account; large river ecology; metapopulation management; Metapopulations; National parks; Natural resources; Navigation; Navigation systems; Nesting; Parks & recreation areas; Population growth; population modeling; Population studies; Regulated rivers; Reviews; River networks; Rivers; Sand bars; Sand beds; sandbar habitat; Sterna antillarum; Subpopulations; threatened and endangered species; Uncertainty; Wildlife conservation; Montana; Mississippi Valley; Missouri River; United States > US; Great Plains; Florida; Arkansas; Nebraska; Mississippi; Texas; Missouri; Gulf of Mexico; Ohio; USA, Mississippi Valley; North America, Mississippi R; population modeling; Dispersal; metapopulation management; large river ecology; sandbar habitat; threatened and endangered species; ecological response to dams and flow alteration
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.726

Interior Least Terns (Sternula antillarum) (ILT) are colonial, fish‐eating birds that breed within active channels of large sand bed rivers of the Great Plains and in the Lower Mississippi Valley. Multipurpose dams, irrigation structures, and engineered navigation systems have been present on these rivers for many decades. Despite severe alteration of channels and flow regimes, regulation era floods have remained effective at maintaining bare sandbar nesting habitat on many river segments and ILT populations have been stable or expanding since they were listed as endangered in 1985. We used ILT breeding colony locations from 2002 to 2012 and dispersal information to identify 16 populations and 48 subpopulations. More than 90% of ILT and >83% of river km with suitable nesting habitat occur within the two largest populations. However, replicate populations remain throughout the entire historical, geophysical, and ecological range of ILT. Rapid colonization of anthropogenic habitats in areas that were not historically occupied suggests metapopulation dynamics. The highest likelihood of demographic connectivity among ILT populations occurs across the Southern Plains and the Lower Mississippi River, which may be demographically connected with Least Tern populations on the Gulf Coast. Paired ecological and bird population models are needed to test whether previously articulated threats limit ILT population growth and to determine if management intervention is necessary and where. Given current knowledge, the largest sources of model uncertainty will be: (1) uncertainty in relationships between high flow events and subsequent sandbar characteristics and (2) uncertainty regarding the frequency of dispersal among population subunits. We recommend research strategies to reduce these uncertainties.
Large multi‐purpose dams, irrigation structures, and engineered navigation systems have resulted in major changes to flow regimes and physical habitat on rivers across the range of federally endangered “interior” Least Terns (ILT). We review historic data on colony locations and dispersal to define discrete ILT population subunits and describe their ecology relative to habitat dynamics that typify the regulation era. We identify major areas of uncertainty to be addressed to improve inferences in population‐level studies ranging from population projection models to the evaluation of management actions.