Sternula antillarum athalassos
Status: Fairly common regular spring and fall migrant central and east, rare west. Locally fairly common regular breeder east and central. State and federally listed as Endangered.
Documentation: Specimen: UNSM ZM6222, 4 Aug 1902 Badger, Holt Co.
Taxonomy: Three subspecies are currently recognized (Gill and Donsker 2017), although these are weakly-differentiated (Pyle 2008); athalassos occurs in central and south-central North America, antillarum occurs in the eastern and southern United States to Honduras, the Caribbean, and northern South America, and browni occurs in central California. All subspecies winter from Central America south to both coasts of South America, as far as Peru and northern Brazil. Nebraska birds are athalassos.
Spring: May 11, 11, 12 <<<>>> summer
Arrival typically does not occur until the latter half of May; there is an earlier report 9 May 2018 in Knox Co. There is a single credible report for Apr of one “well-seen” at Hastings, Adams Co 10 Apr 2005 (Paul Dunbar, pers. comm.); earliest dates for South Dakota are 12 Apr and 3 May (Tallman et al 2002) and for Kansas 15 and 30 Apr (Thompson et al 2011).
Two rather late birds just south of Valentine NWR, Cherry Co 12 Jun 2012 were not in breeding habitat.
This species primarily occurs along rivers and associated habitats (e.g., sand and gravel mines) and is rare elsewhere, as exemplified by the Rainwater Basin, where there are only six spring records (Jorgensen 2012), most recently 19 May 2001, 27 May 2011, and 9 Jun 2007. At an unexpected location were two at Hackberry Lake, Crescent Lake NWR, Garden Co 7 Jun 2016, and one was near Oshkosh, Garden Co 5 Jun 2018.
- High counts: 35 on the lower Platte River 29 May 2009, 14 on the Missouri River, Dixon Co 19 May 2017, and 12 near Columbus on the Platte River 16 May 2012.
Summer: Breeding occurs in the Missouri, Platte, lower Niobrara, lower Loup, and lower Elkhorn river systems. Historically, breeding occurred almost exclusively on river sandbars in these systems, but human alterations to the environment have changed the species’ distribution and habitat use in the state (Sharpe et al 2001). River development (e.g., withdrawals, channelization, and damming) has altered river flows and hydrologic regimes, which, in turn, has led to a general decrease in sandbar habitat (Sharpe et al 2001). However, human activity has also resulted in habitat created incidentally at sand and gravel mines and lakeshore housing developments in Nebraska’s river systems, particularly the Platte River (Brown and Jorgensen 2008, Brown et al 2016). Approximately 90% of Interior Least Terns breed in drainages of the lower Mississippi River, with only about 5% of the population in the upper Missouri River and tributaries, which includes river systems in Nebraska (Lott et al 2013). An exhaustive review of data used in the Adaptive Management modeling process that is part of the US Army Corps of Engineers (USACE) Missouri River Recovery Plan was published by Buenau et al (2015).
Historically, breeding presumably occurred along the entire eastern border of Nebraska. Since the channelization of the Missouri River below Sioux City in the 1950s, breeding regularly occurs only along the remaining un-channelized portion of the river between Gavin’s Point Dam and Sioux City (Sharpe et al 2001). In this river stretch, nesting habitat has been artificially increased at times when sandbar habitat was limited by mechanical methods (e.g., dredging to create artificial sandbars). Nesting also occurs on human-islands in the upper portion of Lewis and Clark Lake and along the Missouri River upstream of the “delta” in Lewis and Clark Lake to the South Dakota border.
A review of survey data for 97 Least Tern breeding sites in the Niobrara, Platte, and Missouri River (bars below Fort Randall and Gavin’s Point dams) for 2002-2011 resulted in a minimum count of 1610 birds (Lott et al 2013). Reduced or declining habitat trends are periodically reversed by major flow events; the 2011 flood event created >14,000 acres of sandbar habitat on the Missouri River (U.S. Army Corps of Engineers 2013). In addition, the 2011 event created small patches of habitat below Sioux City. A single nest was found in an expanse of un-vegetated sand adjacent to the main channel in Burt County in 2012 and a small number apparently nested at Schilling WMA, Cass Co, immediately downstream of the Missouri-Platte River confluence (Pavelka 2012). Small numbers also nested in southwest Iowa (Ubias et al 2014) and northwest Missouri (Eric Hoppes, NRCS, personal communication). Breeding occurred from 1991 to 1994 along Papillion Creek (Silcock and Rosche 1994), a smaller tributary of the Missouri River that empties just above the mouth of the Platte.
Breeding in the Platte River systems extends west to Lake McConaughy, Keith Co, where the species was first discovered breeding in 1989 (Czaplewski 1989), although the first occurrence was in 1977 (Rosche and Johnsgard 1984). Breeding is now annual at protected sites around Lake McConaughy (Brown and Brown 2001). The number of breeding pairs and nests has ranged from two to 29 from 1993 to 2014 (Central Nebraska Public Power and Irrigation District (CNNPID) 2015), although no nests were observed in 2016 (Zorn and Wilson 2016). Small numbers also nest at sand and gravel operations in Lincoln and Keith Counties (Peyton and Wilson 2016). In 2016, four Least Tern nests were found along the South Platte River between Brule and Ogallala when Lake McConaughy was at full pool (Dave Zorn, CNPPID, personal communication). The only record further west is of one at Oliver Reservoir, Kimball Co 16 Jun 2013.
In the central Platte River Valley between Chapman and Lexington, nesting now occurs primarily at off-river sites (Cahis and Baasch 2015). Many off-river sites in this stretch are maintained and managed by the Platte River Recovery Implementation Program (PRRIP) or the Nebraska Public Power District (Cahis and Baasch 2015). Efforts by PRRIP to create suitable habitat in the river channels have had minimal success. The overall number of pairs on the central Platte River has ranged from 39 to 141 during 2007-2015 and has generally increased during that period due to intensive habitat work, primarily at off-river sites (Cahis and Baasch 2015).
In the lower Platte River Valley, between 200 and 400 nests have been recorded since 2008 (Brown et al 2016). The distribution of nesting birds is variable and is associated with habitat conditions on the river. In 2009, as many as 264 nests were located on river sandbars, but in 2015 a total of 310 nests were located at off-river sites while only eight nests, initiated late in the season once water levels declined, were found on river sandbars (Brown et al 2016).
In the Loup system, breeding birds presently occur as far west as Valley Co and Howard Co at off-river habitats. In addition, nesting occurred along the Middle Loup River immediately downstream of the Arcadia Diversion Dam in 1979, 1988 and 1989 near the Custer-Valley Co line and near Arcadia in 1983 (NGPC, unpublished data). Nesting has also occurred along the Niobrara River as far west as Brown and Keya Paha Cos on river sandbars (NGPC, unpublished data) and on the Elkhorn River upstream to Madison Co at off-river sites (NGPC, unpublished data).
The only known nesting away from river systems was the five nests found by Tout (1902) on an exposed bank at what is now Kirkpatrick Basin North WMA, York Co during the summers of 1896 and 1897. Jorgensen (2012) concluded that nesting might occur on occasion in such circumstances, but there are no other breeding records for the Rainwater Basin, and fewer than ten summer records overall in 90 years (Jorgensen 2012). However, this species does nest regularly at Cheyenne Bottoms and Quivira NWR in central Kansas (Thompson et al 2011).
Nesting usually commences in late May shortly after arrival. Least Terns will regularly re-nest if nests initiated early in the season fail; re-nests may be initiated into the latter half of July. However, breeding activity attenuates sharply in August and nests initiated late are often abandoned. Occasionally, tern chicks are abandoned by adults (Jenniges and Plettner 2008).
- Breeding Phenology:
Eggs: 29 May-28 Jul
Nestlings: 6 Jul
Fall: summer <<<>>> Sep 15, 18, 21 (Tout 1947)
Most reports of obvious migrants away from breeding locations begin in late Jul. This species quickly departs in early to mid-August and by late August most are gone. There are later reports, none documented.
- High counts: 25 at Lake North, Platte Co 13 Aug 2006, 24 (including eight juveniles) at Schilling WMA 9 Aug 2009, 23 in western Douglas Co 14 Aug 2015, and 16 at Niobrara, Knox Co 18 Aug 2001.
NGPC: Nebraska Game and Parks Commission
NRCS: Natural Resources Conservation Service
NWR: National Wildlife Refuge
UNSM: University of Nebraska State Museum
WMA: Wildlife Management Area (State)
Mary Bomberger Brown and Lauren R. Dinan reviewed an earlier draft of this species account and provided numerous helpful comments that improved the content and composition.
Brown, C.R., and M.B. Brown. 2001. Birds of the Cedar Point Biological Station. Occasional Papers of the Cedar Point Biological Station, No. 1.
Brown, M.B., L.R. Dinan, and J.G. Jorgensen. 2016. 2016 Interior Least Tern and Piping Plover Monitoring, Research, Management, and Outreach Report for the Lower Platte River, Nebraska. Joint Report of the Tern and Plover Conservation Partnership and the Nongame Bird Program of the Nebraska Game and Parks Commission. Lincoln, Nebraska, USA.
Brown, M.B., and J.G. Jorgensen. 2008. 2008 Interior Least Tern and Piping Plover Monitoring, Research, Management, and Outreach Report For the Lower Platte River, Nebraska. Joint report of the Tern and Plover Conservation Partnership and the Nongame Bird Program at the Nebraska Game and Parks Commission. Lincoln, Nebraska, USA.
Buenau, K.E., C.R. Vernon, V. Cullinan, and C.J. Huber. 2015. Science Information to Support Missouri River Piping Plover and Least Tern Effects Analysis. Richland, Washington, USA.
Cahis, S.D., and D.M. Baasch. 2015. 2014 Interior Least Tern and Piping Plover monitoring and research report for the central Platte River, Nebraska. Platte River Recovery and Implementation Program, Kearney, Nebraska, USA.
Central Nebraska Public Power and Irrigation District. 2015. Land and shoreline management plan three-year endangered species reevaluation report for period ending 2014. Central Nebraska Public Power and Irrigation District Holdrege, Nebraska, USA.
Czaplewski, M.M. 1989. Least Terns at Lake McConaughy. NBR 57: 95-96.
Gill, F., and D. Donsker (Eds). 2017. IOC World Bird List (v 7.3), accessed 30 January 2018.
Jenniges, J.J., and R.G. Plettner. 2008. Least Tern nesting at human created habitats in central Nebraska. Waterbirds 31: 274–282.
Jorgensen, J.G. 2012. Birds of the Rainwater Basin, Nebraska. Nebraska Game and Parks Commission, Lincoln, Nebraska, USA.
Lott, C.A., R.L. Wiley, R.A. Fischer, P.D. Hartfield, and J.M. Scott. 2013. 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. Ecology and Evolution 3: 3613-3627.
Pavelka, G. 2012. Missouri River Navigation Channel Survey for Least Terns & Piping Plovers—2012 Breeding Season. U.S. Army Corps of Engineers, Yankton, South Dakota, USA.
Peyton, M.M., and G.T. Wilson. 2016. Least Tern and Piping Plover Nest Monitoring Final Report 2015. Central Nebraska Public Power and Irrigation District, Holdrege, Nebraska, USA.
Pyle, P. 2008. Identification Guide to North American Birds. Part II, Anatidae to Alcidae. Slate Creek Press, Bolinas, California, USA.
Rosche, R.C., and P.A. Johnsgard. 1984. Birds of Lake McConaughy and the North Platte River Valley, Oshkosh to Keystone. NBR 52: 26-35.
Sharpe, R.S., W.R. Silcock, and J.G. Jorgensen. 2001. The Birds of Nebraska: Their Distribution and Temporal Occurrence. University of Nebraska Press, Lincoln, Nebraska, USA.
Silcock, W.R., and R.C. Rosche. 1994. Spring Field Report, March-May 1994. NBR 62: 66-88.
Tallman, D.A., Swanson, D.L., and J.S. Palmer. 2002. Birds of South Dakota. Midstates/Quality Quick Print, Aberdeen, South Dakota.
Thompson, M.C., C.A. Ely, B. Gress, C. Otte, S.T. Patti, D. Seibel, and E.A. Young. 2011. Birds of Kansas. University Press of Kansas, Lawrence, Kansas, USA.
Tout, W. 1902. Ten years without a gun. Proc NOU 3: 42-45.
Tout, W. 1947. Lincoln County birds. Published by the author, North Platte, Nebraska, USA.
Ubias, R.R., C.W. Lundy, and S.J. Dinsmore. 2014. Least Terns nesting in southwestern Iowa. Iowa Bird Life 84: 143-147.
U.S. Army Corps of Engineers. 2013. Missouri River Recovery Program. Emergent Sandbar Habitat Annual Adaptive Management Report (Year 3: 2012), March 2013. U.S. Army Corps of Engineers, Yankton, South Dakota,USA.
Zorn, D.J., and G.T. Wilson. 2016. Least Tern and Piping Plover Nest Monitoring Final Report 2016. Central Nebraska Public Power and Irrigation District, Holdrege, Nebraska, USA.
Silcock, W.R., and J.G. Jorgensen. 2017. Least Tern (Sternula antillarum athalassos), Version 1.0. In Birds of Nebraska — Online. www.BirdsofNebraska.org