Basic Information
Common Name: California Least Tern
Scientific Name: Sternula antillarum browni
Species Code: STEANT
Management Category: SO (significant occurrence at risk of loss)
Occurrence Map
Table of Occurrences
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Species Information

MSP Species Background

Goals and Objectives

Goal: Protect, enhance, and restore California least tern occupied and historically occupied habitat to create resilient, self-sustaining populations that provide for persistence over the long-term (>100 years).

local NFO 2017, 2018, 2019, 2020, 2021 SO
MGT-IMP-PRED STEANT-1

Management units: 1, 7

From 2017-2021, annually conduct predator control at breeding least tern colonies before and during the nesting season to improve fledgling success. Include tracking of predator-tern interactions to provide real-time data to improve control efforts during the breeding season.

Action Statement Action status Projects
IMP-1 Conduct predator control prior to breeding and during the breeding season to control the various taxa (e.g. mammals, reptiles, birds, inverebrates) that prey on adult, nestling, and fledgling least terns. in progress
IMP-2 Submit data and reports to MSP web portal. in progress
Criteria Deadline year
Predator Control Implemented and Reports Completed Annually 2021
local NFO 2017, 2018, 2019, 2020, 2021 SO
MON-IMP-PRED STEANT-2

Management units: 1, 7

From 2017-2021, monitor the effectiveness of predator control at least tern colonies and monitor overall tern predator status and trend to identify larger issues potentially affecting other MSP species and to improve management effectiveness.

Action Statement Action status Projects
IMP-1 Submit monitoring data and reports to MSP web portal available for implementation
Criteria Deadline year
Monitoring completed and data and report submitted within 1 year of management actions being completed. 2021
regional NFO 2017, 2018, 2019, 2020, 2021 SO
MON-SURV-SPEC STEANT-3

Management units: 1, 7

From 2017 to 2021, continue the existing survey efforts for California least tern implemented by the wildlife agencies and military.

Action Statement Action status Projects
SURV-1 Submit monitoring data and management recommendations to MSP web portal In progress
Criteria Deadline year
Least Tern Surveys and Reports Completed Annually 2021
local NFO 2017, 2018, 2019, 2020, 2021 SO
MON-IMP-IMG STEANT-4

Management units: 1, 7

From 2017 to 2021, annually inspect the existing nest sites for California least tern, taking precautions to avoid disturbance during the nesting season, to identify necessary management actions in order to support the expansion of the occurrence to self sustaining levels.

Action Statement Action status Projects
IMP-1 Conduct regional IMG monitoring protocol survey locations and habitat, assess status, and quantify potential threats. Available for implementation
IMP-2 Based upon threat evaluation, determine if routine management or more intensive management is warranted. Available for implementation
IMP-3 Submit monitoring data and management recommendations to MSP web portal Available for implementation
Criteria Deadline year
Surveys Completed Annually with management recommendations 2021
local NFO 2017, 2018, 2019, 2020, 2021 SO
MGT-IMP-IMG STEANT-5

Management units: 1, 7

From 2017-2021, perform routine management activities such as invasives removal, sand replenishment, nest prep, and protecting occurrences from disturbance through fencing, signage, and enforcement.

Action Statement Action status Projects
IMP-1 Perform management activities protecting occurrences from disturbance through fencing, signage, and enforcement. Available for implementation Adaptive Management of Coastal Sand Dunes in Mission Bay to Benefit Native Plants and the CA Least Tern
IMP-2 Submit project metadata and management data to MSP web portal. Available for implementation Adaptive Management of Coastal Sand Dunes in Mission Bay to Benefit Native Plants and the CA Least Tern
Criteria Deadline year
Management Completed as Needed Based Upon Monitoring Recommendations 2021
Adaptive Management of Coastal Sand Dunes in Mission Bay to Benefit Native Plants and the CA Least Tern
San Diego Audubon has been leading efforts to restore coastal sand dunes in Mission Bay for decades, largely focused on supporting nesting California Least Terns (Sternula antillarum browni), and rare and endangered sand dune plants such as Nuttall's Lotus (Acmispon prostratus) and Coast Wooly Head (Nemacaulis denudata). The primary threat to these species is the presence of fast-growing, nonnative vegetation, which takes up space that Least Terns require for nesting, and outcompetes native dune plants. Volunteer-led hand management of these sites has resulted in a dramatic reduction in invasive cover, and bi-annual vegetation monitoring has revealed that hand management is a more effective strategy in reducing nonnative growth than the more traditional mechanized scraping and broadcast herbicide application strategies. These results are being used to inform year-to-year site management, and to create longterm strategies for managing coastal dunes in Mission Bay.
California Least Tern Predator Monitoring (Ternwatchers)
Volunteer-based predator monitoring program at the nesting sites in Mission Bay. Citizen scientists are trained to monitor nesting sites for predators from mid-April through late May, with the program concluding the end of September.
North County Dunes Restoration
Phase I of this project focused on surveys and restoration activities at potential dune habitat between northern Carlsbad and northern La Jolla. This was in order to extend the range and increase the population of dune-dependent species, such as the California least tern, Western snowy plover, and Nuttall's lotus. Phase 2 will focus on the completion and implementation of the following site-specific restoration plan that was developed during the first phase of the project: the Cardiff State Beach Living Shorelines Draft Habitat Restoration Plan. In addition, SELC proposes to conduct invasive species management and support existing populations of special-status/native coastal dune and bluff plant species at South Carlsbad State Beach Campground.
File name Lead Author Year Type
CALIFORNIA LEAST TERN BREEDING SURVEY 1993 Season Caffrey, Carolee 1994 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1994 SEASON Caffrey, Carolee 1995 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1995 Season Caffrey, Carolee 1997 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1996 Season Caffrey, Carolee 1998 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1997 Season Keane, Kathy 1998 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1998 Season Keane, Kathy 1999 report
CALIFORNIA LEAST TERN BREEDING SURVEY 1999 Season Keane, Kathy 2001 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2000 SEASON Patton, Robert T. 2001 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2004 Season Marschalek, Dan 2005 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2005 Season Marschalek, Dan 2006 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2006 Season Marschalek, Dan 2007 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2007 Season Marschalek, Dan 2008 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2008 Season Marschalek, Dan 2009 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2009 Season Marschalek, Dan 2010 report
California Least Tern Breeding Survey 2010 Season Marschalek, Dan 2011 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2011 Season Marschalek, Dan 2012 report
CALIFORNIA LEAST TERN BREEDING SURVEY 2012 Season Frost, Nancy 2013 report
California least Tern Breeding Survey 2014 Season Frost, Nancy 2015 report
California Least Tern Breeding Survey 2015 Season Frost, Nancy 2016 report
California Least Tern Breeding Survey 2016 Survey Frost, Nancy 2017 report
California Least Tern Breeding Survey 2017 Season Sin, Hans 2021 report
City of Carlsbad Habitat Management Plan Annual Report and Monitoring Summary Year 7, Nov. 2010 - October 2011 2012 report
Final Mission Bay Park Natural Resource Management Plan 1990 report
Final Report for Grant Agreement #5001768 – North County Dunes Restoration (Coastal Species) Gibson, Doug 2016 report
Final Report Mission Bay Park Redfern, Chris 2015 report
Final Report: SD Bay National Wildlife Refuge: California Least Tern and Western Snowy /plover Recovery at D Street Nesting Site 2015 report
Final Report: Threatened and Endangered Species Stewardship at D Street Fill Kramp, Heather; Maher, Eileen 2020 report
Maps of treatment and monitoring sites for California least tern on Mission Bay 2012 other
Mission Bay IBA Conservation Planning Quarterly Report 2012 report
Mission Bay IBA Conservation Planning Workshop Summary 2012 workshop summary
Mission Bay Park Conservation Program: Habitat Assessment, Invasive Control, and Community-Based Habitat Restoration Redfern, Chris 2013 powerpoint presentation
Nuttall's Lotus: Final Report Redfern, Chris; Flaherty, Megan 2018 report
Recording - September 2020 SDMMP Management and Monitoring Coordination Meeting Sin, Hans; Merlos, KariLyn 2020 recording
Revised California Least Tern Recovery Plan 1985 other
Saltwork Nest History 2008 other
San Diego Association of Governments CA least tern predator monitoring by SDAS Final Report 2017 report
San Diego Audubon Society Research Study: Project proposal and methods 2012 report
STATUS OF THE ENDANGERED CALIFORNIA LEAST TERN: POPULATION TRENDS AND INDICATORS FOR THE FUTURE Keane, Kathy; Langdon, Spencer; Mudry, Nathan 2010 fact sheet
Ternwatchers, San Diego Audubon 2016 powerpoint presentation
Updates on California Least Tern Management at SDIA Merlos, KariLyn 2020 powerpoint presentation
Venice Beach Least Tern Colony Habitat Improvement and Restoration Study, 2006-2009 Ryan, Thomas; Vigallon, Stacey; Dunno, Glenn; Magier, Shelly; Delnevo, Adrian 2010 report

Current Distribution Rangewide

Found along the Pacific Coast of California, from San Francisco southward to Baja California, and in Chiapas, and Jalisco during the breeding season [1;2]. Wintering likely from Baja California to southern Mexico or along the Pacific coast of Central America and north to at least Colima, Mexico [3 cited from 2].

Known Populations in San Diego County

Occurrences found in Camp Pendleton, Borderfield State Park, San Diego Bay National Wildlife Refuge, Fiesta Island, Flood Control Channel Southern Wildlife Preserve, Mariner's Point, Mission Bay Park, Silver Strand State Beach, Agua Hedionda Lagoon Ecological Reserve, San Luis Rey River Park, Tijuana Slough National Wildlife Refuge, Torrey Pines State Natural Reserve, Batiquitos Lagoon Ecological Reserve, Buena Vista Lagoon Ecological Reserve, Agua Hedionda-SDGE, San Elijo Lagoon Ecological Reserve, Cardiff State Beach, James Scripps Bluffs Preserve, and San Dieguito Lagoon.

List Status

FE, CE

Habitat Affinities

Nest in colonies on relatively open, flat beaches kept free of vegetation by natural scouring from tidal action and along lagoon or estuary margins [1;3 cited from 2]. Forages along seacoasts, beaches, bays, estuaries, lagoons, lakes, and rivers [5 cited from 2]. Rests and loafs on sandy beaches, mudflats, and salt-pond dikes [6 cited from 2].

Taxonomy and Genetics

A subspecies of least terns where two other subspecies, Interior (S. a. athalassos) and Eastern (S. a. antillarum), are recognized in the United States [7 cited from 4]; however, there is little genetic variation among the subspecies which questions the validity of this division [8 cited from 4]. A taxonomic change by the American Ornithologists' Union (AOU) [9 cited from 4] resurrected the genus Sternula for the least tern based on genetic studies.

Seasonal Activity

Fall migration commences the last week of July and first week of August. Several weeks before the Fall Migration, adults and young wander along marine coastlines, congregating at prime fishing sites. In the autumn, adults move south along the california coast with their fledglings stopping to rest and feed along the migration route [2;10 cited from 1].

Life History/Reproduction

Arrive at California nesting sites in late April, where courtship and pair formation activities last into early May [10 cited from 11]. Typical colony size is 25 pairs [1]. Egg-laying and incubation generally begins in mid-May, and pairs may renest following loss of their first clutch [12]. Nests are simple scrapes made on non-vegetated substrates, usually consisting of one to three eggs, and are incubated for 19-25 days by both parents [1;10 cited from 11;13 cited from 4]. Chicks are mobile and leave the nest at only two days after hatching, the semi-precocial young are tended by both parents, and first flight happens at approximately 20 days after hatching [10 cited from 11;13 cited from 4]. Usually start breeding in their third year, but it is not uncommon to start in their second year. Can re-nest up to two times if eggs or chicks are lost early in the breeding season [1;12]. Usually nests in same area in successsive years; tends to return to natal site to nest [14]. Very gregarious and forage, roost, nest and migrate in colonies [1]. A long-lived species and banded birds have been recovered after 24 years [4].

Diet and Foraging

Prey species captured and consumed are remarkably similar across a broad geographic range including the San Fransisco Bay, southern California, and the Gulf of California off Baja Mexico [11;15;16]. Most abundant prey species selected in California are northern anchovies (Engraulis mordax), topsmelt (Atherinops affinis), jacksmelt (Atherinopsis californiensis), deepbody anchovies (Anchoa compressa), and slough anchovies (Anchoa delicatissima). For coastal birds, preference for nearshore foraging habitats is apparently related to prey species selection as northern anchovies, topsmelt, and jacksmelt (all marine species) comprise 92% of captured fish [15].

Dispersal

No information.

Threats

Threats to tern colonies include predation, human disturbance, and nonnative plants. Other threats to terns are food shortage and environmental contamination [1].

Literature Sources

[1] U.S. Fish and Wildlife Service. 2006. California Least Tern (Sternula antillarum browni) 5-Year Review Summary and Evaluation. Carlsbad Fish and Wildlife Office, Carlsbad, California, USA.

[2] NatureServe. 2015. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available from ttp://explorer.natureserve.org. Accessed: September 28, 2016.

[3] Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1992. Birds in Jeopardy: the Imperiled and Extinct Birds of the United States and Canada, Including Hawaii and Puerto Rico. Stanford University Press, Stanford, California. 259 pp.

[4] California Department of Fish and Wildlife. 2016. California Least Tern Breeding Survey 2015 Season. South Coast Region, San Diego, California, USA.

[5] American Ornithologists' Union (AOU). 1983. Check-list of North American Birds, 6th edition. Allen Press, Inc., Lawrence, Kansas. 877 pp.

[6] Stiles, F. G. and A. F. Skutch. 1989. Guide to the birds of Costa Rica. Comistock.

[7] American Ornithologists’ Union (AOU). 1957. Check-list of North American Birds, 5th Ed. American Ornithologists’ Union, Ithaca.

[8] Whittier, J. B., D. M. Leslie Jr., and R. A. Van Den Bussche. 2006. Genetic variation among subspecies of Least Tern (Sterna antillarum): implications for conservation. Waterbirds 29, no. 2: 176-184.

[9] Banks, R. C., C. Cicero, J. L. Dunn, A. W. Kratter, P. C. Rasmussen, J. V. Remsen Jr, J. D. Rising, and D. F. Stotz. 2006. Forty-Seventh Supplement To The American Ornithologists' Union Check-List Of North American Birds. The Auk 123, no. 3: 926-936.

[10] Thompson, B. C., J. A. Jackson, J. Burger, L. A. Hill, E. M. Kirsch and J. A. Atwood. 1997. Least Tern (Sterna antillarum). In Birds of North America, No. 290 (A. Poole and F. Gill, Eds.). The Academy of Natural Sci- ences, Philadelphia, PA, and The American Ornithologists' Union, Washington, DC.

[11] Elliott, M. L., R. Hurt, and W. J. Sydeman. 2007. Breeding biology and status of the California least tern Sterna antillarum browni at Alameda Point, San Francisco Bay, California. Waterbirds 30, no. 3: 317-325.

[12] Massey, B. W. and J. L. Atwood. 1981. Second-wave nesting of the California Least Tern: age composition and reproductive success. The Auk: 596-605.

[13] U.S. Fish and Wildlife Service. 1985. Recovery plan for the California least tern, Sterna antillarum browni.

[14] Atwood, J. L. and B. W. Massey. 1988. Site fidelity of least terns in California. Condor: 389-394.

[15] Atwood, J. L. and P. R. Kelly. 1984. Fish dropped on breeding olonies as indicators of Least Tern food habits. The Wilson Bulletin: 34-47.

[16] Zuria, I. and E. Mellink. 2005. Fish abundance and the 1995 nesting season of the Least Tern at Bahia de San Jorge, northern Gulf of California, Mexico. Waterbirds 28, no. 2: 172-180.