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The California Least Tern (CLT) is a small seabird that nests in several protected nesting sites on the coast of California, USA, as well as parts of coastal Mexico. Following listing as an endangered species, the California population1 increased from 664 in 1976 to approximately 7,000 in 2009. The majority of the increase occurred during the 1990's, following the initiation of focused predator management. Despite ongoing protection efforts, egg and chick predation by several avian and mammalian species at many sites, as well as fluctuations in prey abundance and chronology, have resulted in low reported levels of productivity2 in recent years. Thus, although annual estimates of breeding pairs suggest a continued slow increase, many CLT researchers predict a sudden population decline. However, estimates of breeding pairs and fledglings are not systematically and consistently calculated. Thus, we analyzed several other breeding variables derived from field data. Results suggest large annual variations, but, aside from a statisticallysignificant decline in clutch size, no significant change over time in egg abandonment, egg predation, chick/fledgling mortality or chick/fledgling predation.

Burrowing Owl (Athene cunicularia) populations in San Diego County appear to have decreased through the early 1900s in conjunction with human population growth and concomitant habitat loss. By the late 1970s/early 1980s, there were perhaps 250-300 pairs left, but as of 2003 the population had been reduced to no more than 25-30 resident pairs (note: recent surveys revealed additional owls suggesting that there were, at most, 46 pairs in the county as of 2007). Primary threats to the remaining small Burrowing Owl population in San Diego County are reduced habitat suitability and fragmentation of remaining suitable habitat; conflicts with management of listed species, especially the California Least Tern (Sterna antillarum browni) and Western Snowy Plover (Charadrius alexandrinus nivosus); and human disturbance (including their pets and vehicles). In addition, predators, prey abundance and availability, and colony size are likely factors influencing population dynamics, the relative importance of which are difficult to characterize. Given county owl population declines and current threats, a comprehensive management program is essential to protect remaining habitat and owls. If such a plan, or similar action, is not implemented soon, extirpation of the Burrowing Owl in San Diego County seems imminent.

Once the beaches of southern California teemed with California least terns [Sterna antillarum (=albifrons) browni]. Today, least tern numbers are so depleted that both the U.S. Fish and Wildlife Service (Federal Register 35:16047, October 13, 1970; Federal Register 35:8495, December, June 2, 1970) and California Fish and Game Commission (California Department of Fish and Game 1980) consider the subspecies in danger of extinction and classify it as an endangered species. The goals of this recovery plan are to prevent extinction and return the California least tern population to a stable, nonendangered status. The plan summarizes available biological information on the terns, identifies their ecologic needs, and proposes orderly and comprehensive actions to restore them to a viable population and ultimately to delist the species.

Monitoring of nesting sites in 2000 resulted in an estimate of 4521 to 4790 breeding pairs of California least terns establishing 5301 nests at 37 locations. This represents a 31 percent increase in the minimum estimated number of breeding pairs from 1999. An estimated 3710 to 4013 fledglings were produced, or 0.77 to 0.89 fledglings per pair. This represents a 453 percent increase over productivity of the 1999 season, and 38 percent over that of 1998. Depredation was the primary limiting factor to reproductive success. Other reported causes of mortality included a heat wave in the San Francisco Bay area, nest abandonment, and human activity, including loss of chicks to vehicles. The nesting colony at Camp Pendleton continues to be the largest in the state, accounting for 22.8 percent of breeding pairs and producing 27.6 percent of this season's fledglings. Other colonies numbering over 200 nests included Alameda Point, Point Mugu, Venice Beach, L.A. Harbor, Huntington State Beach, Mariner's Point, Naval Amphibious Base Coronado North Delta Beach and ocean beach, and Tijuana Estuary. The nesting site first documented in 1998 at Tulare Lake bed evaporation ponds outside of Kettleman City in Kings County was used again in 2000, and newly created Caltrans mitigation islands in Albany in Alameda County were colonized and produced at least one fledgling.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2017, with a known 29 active nesting sites providing data, a decrease of 5 active nesting sites from 2016. An estimated 4097-5598 tern breeding pairs established 5983 nests and produced 1131-1655 fledglings across California. The fledgling to breeding pair ratio was 0.2 to 0.4. Statewide, 9518 eggs were reported, with an average clutch size of 1.72 eggs. Camp Pendleton, Naval Base Coronado, Batiquitos, Point Mugu, Huntington, and Alameda Point each had over 300 minimum nests (same sites with > 300 nests in 2016), which represented 75% of the state nest total, and produced 65% of the state’s fledglings. Overall least tern mortality (combined life stages of egg, chick, fledgling, and adult) due to non-predation factors was greater than mortality due to predation in 2017. However, predation mortality for eggs and adults was greater than non-predation mortality. Of the non-predation egg mortality events, the highest cause of failure was attributed to abandonment prior to the expected hatching date and post-term. With the expressed consent of Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE) and Terra Peninsular we are able to report California least tern breeding data for the first time on the Baja peninsula. For 2017, a total of 472 pairs were reported from Ensenada to as far south as La Paz. These surveys were conducted by a team of researchers that visited 27 of the known 31 nesting sites during the breeding season. Least terns were also observed in the State of Hawaii on the Island of Hawai'i in 2017. Monitors reported the presence four pairs producing six fledglings at Kohana'iki on the leeward side of the island, with the nesting season occurring from April through July (Baird et al. 2017). These species were confirmed to be least terns by genetic analysis and have been observed nesting on the Island of Hawai'i since 2012 (Scott Waddington, pers. comm., 2012, Baird et al. 2014).

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2012, with observers at 41 nesting sites providing data. An estimated 4293-6421 California least tern breeding pairs established 6636 nests and produced 557-628 fledglings at 49 documented locations. The fledgling to breeding pair ratio was 0.09 to 0.15. Statewide, 11,036 eggs were reported, with a Site Mean clutch size of 1.66 eggs per nest (St Dev = 0.134) and a Statewide clutch size of 1.65 eggs (St Dev = 0.492) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Naval Base Coronado, Point Mugu, Batiquitos Lagoon Ecological Reserve, Camp Pendleton, Huntington State Beach, and Alameda Point represented 74% of the breeding pairs. Fledgling numbers were also unevenly distributed as the two sites with at least 90 fledglings each (Hayward and Huntington State Beach) contributed 38% of the state’s production, and the five sites with greater than 35 fledglings each (Hayward, Huntington State Beach, Oceano Dunes, Seal Beach, and Lindbergh Field) contributed 59% of the state’s production. The 2012 chick mortality rate was 49%, continuing the upward trend observed in the previous four years. With the exception of Batiquitos Lagoon and Camp Pendleton, the larger nesting colonies experienced chick mortality rates less than the average, which is opposite that documented in 2011. The most commonly-reported possible, suspected, or documented predators were common ravens (Corvus corax), American crows (Corvus brachyrhynchos), peregrine falcon (Falco sparverius), great-blue herons (Ardea herodias), American kestrels (Falco sparverius), and red-tailed hawks (Buteo jamaicensis). The predators known to be responsible for the greatest number of depredated least terns in 2012 were American kestrel, coyote (Canis latrans), common raven, American crow, unknown avian species, unknown gull species, gull-billed tern (Gelochelidon nilotica), red-tailed hawk, peregrine falcon, and northern harrier (Circus cyaneus). The monitoring effort of 2012 is scheduled to continue in 2013.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2008, with observers at 36 nesting sites providing data. An estimated 6998-7698 California least tern breeding pairs established 8223-8226 nests and produced 2254- 2573 fledglings at 47 documented locations. The fledgling to breeding pair ratio was 0.29-0.37. Statewide, 13,847 eggs were reported, with a Site Mean clutch size of 1.77 eggs per nest (St Dev = 0.124) and the statewide clutch size of 1.75 eggs (St Dev = 0.452) for Type 1 sites (clutch sizes for each nesting site are provided for 2004-2008). Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos Lagoon, Los Angeles Harbor, and Venice Beach represented 64% of the breeding pairs while Alameda Point, Venice Beach, Huntington Beach and Los Angeles Harbor produced 50% of the fledglings. The 2008 chick mortality rate of 14% represented the first increase since 2004 but the actual rate was less than those of 2004 (32%) and 2005 (28%). Camp Pendleton, Venice Beach, LA Harbor, Seal Beach, and Batiquitos Lagoon Ecological Reserve represented 87% of the total reported chick deaths, but only 45% of the total chicks. The main predator of least terns in 2008 was the American crow (Corvus brachyrhynchos), resulting from depredation of 760 eggs at Venice Beach. Gull-billed tern (Gelochelidon nilotica), common raven (Corvus corax), and coyote (Canis latrans) predation each comprised 8-10% of all predation. Common ravens, peregrine falcons (Falco peregrinus), American crows, gulls (Larus sp.), great blue herons (Ardea herodias) and American kestrels (Falco sparverius) were reported from the most sites. The monitoring effort of 2008 is scheduled to continue in 2009.

Approximately 4,017 pairs of California least terns (Sterna antillarum browni) nested at 38 sites along the coast of California in 1997, as reported by least tern monitors. This represents a 19%increase from 1996 pair estimates, and a 55% increase from 1995 pair estimates, more than compensating for the 7% decrease between 1994 and 1995. Recruitment cannot entirely account for this increase in least tern pairs, as reported fledgling production for both 1994 and 1995 was low. Immigration from other least tern populations has been suggested, and improved survival on wintering grounds may be a factor, but supporting data for these hypotheses are lacking. Overestimates of pair numbers and/or underestimates of fledglings by monitors may also partially explain this apparent increase. Reported pair and fledgling values are always imprecise estimates that are not scientifically derived; moreover, consistent methods for obtaining them, as recommended in annual monitoring packets, are not being used at all nesting sites. Reproductive success and adult survival in 1997 was affected by a number of predators, particularly at San Diego County sites. However, fledgling estimates (3,140 to 3,322) for 1997 were 55% to 64% higher than 1996 and 200% higher than 1995 estimates. The statewide fledglings-per-pair value (0.78 to 0.83) was also higher than for the previous three years. San Diego County supported over 57% of 1997 statewide pairs and produced over 58% of statewide fledglings at 20 nesting sites; the Santa Margarita River nesting sites alone supported over 18% of statewide pairs. More than 50%of the statewide breeding population was concentrated in six nesting sites (NAS Alameda, Venice Beach, Huntington Beach, Santa Margarita River North Beach, Mariner's Point, and Delta Beach North); these sites also produced over 64% of the State's fledglings. Santa Margarita River North Beach and NAS Alameda had the highest (over 1.2) fledglings-per-pair values. The Tijuana River nesting sites reported the lowest fledglings-per-pair value (0.01 - 0.02) in the State due to unprecedented burrowing owl predation on adults, a host of other predators in the site vicinity, and human disturbance and intrusion into the nesting site. No evidence of local prey shortages was reported by monitors for any nesting site in 1997.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2015, with observers at 41 nesting sites providing data. An estimated 4202-5295 California least tern breeding pairs established 5504 nests and produced 1514-1887 fledglings at 49 documented locations across California. The fledgling to breeding pair ratio was 0.29 to 0.45. Statewide, 9654 eggs were reported, with a Statewide clutch size of 1.7 eggs (St Dev = 0.26) for Type 1 sites where monitors walk within the colony. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Huntington, Point Mugu, and Alameda Point each had over 300 minimum breeding pairs, which represented 64% of the state total, and produced the most fledglings, contributing 60% of the state’s production (Table 1). Sites with greater than 35 fledglings each (the five aforementioned sites plus Mariner's Point, Hayward, Batiquitos, Bolsa Chica, and Oceano Dunes) contributed 86% of the state’s production. The 2015 statewide non-predation chick mortality rate was 18%, similar to that in 2014 (20%). With the exceptions of Camp Pendleton and Naval Base Coronado, the larger nesting colonies experienced non-predation chick mortality rates less than the average, similar to that documented in 2014. The predators known to be responsible for the greatest number of depredated least terns in 2015 were coyotes (Canis latrans), common ravens (Corvus corax), corvid species, raptor species, peregrine falcons (Falco peregrinus), and American crows (Corvus brachyrhynchos). The monitoring effort of 2015 is scheduled to continue in 2016.

Monitoring to document breeding success of California least terns (Sterna antillarum browni) continued in 2005, with observers at 28 nesting sites providing data. An estimated 6865-7341 California least tern breeding pairs established 8120 nests and produced 1721-2471 fledglings at 42 documented locations. The fledgling to breeding pair ratio was 0.23-0.36. Statewide, 13,752 eggs were reported, with a site average of 1.74 eggs per nest (St Dev = 0.111) and an average clutch size of 1.67 eggs (St Dev = 0.659) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Los Angeles Harbor, Naval Base Coronado, Batiquitos Lagoon and Pt. Mugu represented 68% of the breeding pairs while Los Angeles Harbor, Camp Pendleton, Bolsa Chica Ecological Reserve, Alameda Point, Naval Base Coronado and Batiquitos Lagoon Ecological Reserve produced 76% of the fledglings. Only two sites, Los Angeles Harbor and Camp Pendleton, produced 44% of the statewide fledgling total. Four large sites (Alameda Point, Los Angeles Harbor, Camp Pendleton and Batiquitos Lagoon) experienced high levels of chick mortality. Starvation is a suggested cause of the 33-49% chick death rate. The main predators of least tern chicks were American kestrels (Falco sparverius), American crows (Corvus brachyrhynchos) and coyotes (Canis latrans), accounting for up to 297, 287 and 170 deaths, respectively. Coyotes were reported from the most sites. The monitoring effort of 2005 is scheduled to continue in 2006.

In 1994, a minimum of approximately 2,792 pairs of the endangered California least tern (Sterna antillarum browni) nested at 36 sites along the coast of California. This 20% increase over 1993 breeding population size continues the trend since 1987 of continued growth of the population, and is directly attributable to the efforts of people working on behalf of recovery of the species. The statewide total of 2,792 pairs is the highest number recorded since systematic monitoring began in 1973, and represents a four-and-a-half-fold increase over the estimated 600 pairs of that year. Unfortunately, in 1994, heavy predation pressure at many sites and an apparent food shortage at two large sites, combined with a variety of human-related constraints on tern reproductive success, resulted in poor fledgling production statewide. A minimum of approximately 1755-1871 fledglings were produced, 11% fewer than in 1993, resulting in a statewide fledgling per pair ratio of 0.62-0.67. Documented and suspected predator species across the State ran the usual gamut; however, kestrels, crows, ravens, rats, and a peregrine falcon were responsible for the loss of the majority of terns and tern eggs lost to predation in 1994. As usual, successful and unsuccessful sites were distributed throughout the state. Terns themselves were more unevenly distributed: 48% of the statewide population bred at only four sites (Venice Beach, Huntington Beach, Santa Margarita River/North Beach, Mission Bay/FAA Island); inclusion of an additional five sites (NAS Alameda, Seal Beach, Bolsa Chica, Delta Beach/North, Tijuana River/South) accounted for 76% of all breeding pairs. And, again as usual, the bulk of fledglings produced statewide came from only a few sites; those produced at NAS Alameda, Venice Beach, Seal Beach, Santa Margarita River/North Beach, Mission Bay/FAA Island, and Delta Beach North comprised approximately 70% of the State total.

An estimated 3,451 to 3,674 pairs of California least terns nested at 36 nesting sites in 1999 and produced an estimated 671 to 711 fledglings. These estimates result in 0.18 to 0.21 fledglings per pair, the lowest productivity recorded since statewide censuses were initiated in 1976. Statewide pair estimates decreased 11% from 1998 values, but fledgling estimates declined by 74.9% due to exceedingly high predation and chick mortality at many sites. Over 30% of the nesting population was concentrated at two sites (Mission Bay Mariner's Point and Santa Margarita North Beach); ten sites supported a combined total of 76.6% of statewide pairs. One site (Los Angeles Harbor) contributed nearly 24% of the state's fledglings in 1999; Los Angeles Harbor and three other sites (NAS Alameda, Ormond Beach and Mission Bay Mariner's Point) produced over 50% of 1999 statewide fledglings. Four sites that supported least tern pairs in 1998 reported no nesting in 1999 (Batiquitos Lagoon W-1 and E-2; Mission Bay Fiesta Island, Mission Bay South Shores); four additional sites (Venice Beach, Seal Beach, Bolsa Chica, Chula Vista Wildlife Refuge) supported nesting but had no productivity in 1999. 1999 pair estimates were 18% lower than corresponding statewide nest numbers; in 1998 they differed by only 9%. Renesting may have occurred far less frequently in 1999 than in 1998 due to far higher predation (16.5% of all eggs and 7.7% of chicks hatched) and other factors contributing to chick mortality (26.5% of all hatched eggs) in 1999. The greatest egg losses in 1999 were attributed to coyotes, crows and ravens; highest chick/fledgling losses were to American kestrels, coyotes and peregrine falcons. Chick mortality due to factors other than predation was 26.5%, higher than 1997 and 1998 and is believed to be related to prey deficiencies and unknown factors.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2016, with observers at 42 nesting sites providing data. An estimated 3989-4661 California least tern breeding pairs established 4746 nests and produced 1612-2000 fledglings at 50 documented locations across California. The fledgling to breeding pair ratio was 0.35 to 0.50. Statewide, 7891 eggs were reported, with a Statewide clutch size of 1.37 eggs (St Dev = 0.64) for Type 1 sites where monitors walk within the colony. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos, Point Mugu, Huntington, and Alameda Point each had over 300 minimum breeding pairs, which represented 72% of the state total, and produced 63% of the state’s fledglings. Sites with greater than 35 fledglings each (the five aforementioned sites plus Hayward, LA Harbor, Huntingon, Bolsa Chica, and Oceano Dunes) contributed 88% of the state’s fledgling production. Least tern mortality due to non-predation factors was greater than mortality due to predation in 2016. Of non-predation egg mortality events, the highest cause of failure was attributed to abandonment prior to the expected hatching date and abandonment post-term. The 2016 statewide non-predation chick mortality rate was 29%, higher than that in 2015. The number of fledglings and adults that died in 2016 due to non-predation factors was similar to that in 2015. The predators known to be responsible for the greatest number of depredated least terns in 2016 were peregrine falcons, rats, common ravens, northern harriers, and coyotes. The monitoring effort of 2016 is scheduled to continue in 2017.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2011, with observers at 40 nesting sites providing data. An estimated 4826-6108 California least tern breeding pairs established 6435 nests and produced 1038-1195 fledglings at 49 documented locations. The fledgling to breeding pair ratio was 0.17-0.25. Statewide, 11,140 eggs were reported, with a Site Mean clutch size of 1.76 eggs per nest (St Dev = 0.111) and the Statewide clutch size of 1.75 eggs (St Dev = 0.459) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos Lagoon Ecological Reserve, Huntington Beach, Pt. Mugu and Alameda Point represented 79% of the breeding pairs while Alameda Point, Camp Pendleton, Huntington Beach, Naval Base Coronado and Tijuana River NERR produced 55% of the fledglings. The 2011 chick mortality rate of 20% is slightly greater than the last three years. Alameda Point, Batiquitos Lagoon Ecological Reserve, Camp Pendleton, Huntington State Beach and Naval Base Coronado represented 87% of the total reported chick deaths, but only 70% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2011 were unknown avian species, American crows (Corvus brachyrhynchos), gull species (Laris sp.), peregrine falcons (Falco peregrinus), gull-billed terns (Gelochelidon nilotica), and common ravens (Corvus corax). Common ravens, peregrine falcons, American crows, American kestrels (Falco sparverius), red-tailed hawks (Buteo jamaicensis), and coyotes (Canis latrans) were reported from the most sites. The monitoring effort of 2011 is scheduled to continue in 2012.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2007, with observers at 35 nesting sites providing data. An estimated 6744-6989 California least tern breeding pairs established 7667 nests and produced 2293-2639 fledglings at 48 documented locations. The fledgling to breeding pair ratio was 0.33-0.39. Statewide, 12,238 eggs were reported, with a Site Mean clutch size of 1.67 eggs per nest (St Dev = 0.133) and the statewide clutch size of 1.62 eggs (St Dev = 0.493) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Los Angeles Harbor, and Batiquitos Lagoon represented 55% of the breeding pairs while Venice Beach, Camp Pendleton, Huntington Beach and Naval Base Coronado produced 52% of the fledglings. Although the state experienced a lower chick mortality rate (9%) for the third consecutive year, four of the largest sites (Alameda Point, Venice Beach, Batiquitos Lagoon and Camp Pendleton) experienced levels of chick mortality greater than the state average. These four sites reported 42% of the total chicks, but 79% of the dead chicks. The main predators of least terns in 2007 were unknown species, black-crowned night-herons (Nycticorax nycticorax) and gull-billed terns (Gelochelidon nilotica). Coyote (Canis latrans) and American crow (Corvus brachyrhynchos) predation was lower compared to previous years, but predation due to protected species appears to be increasing. Gulls (Larus sp.) and peregrine falcons (Falco peregrinus) were reported from the most sites. The monitoring effort of 2007 is scheduled to continue in 2008.

In 1996, 3330-3392 pairs of the endangered California least tern (Sterna antillarum nested at 35 sites along the coast of California. This 29% increase in breeding population size over 1995 resumes the predominant pattern since 1987 of exponential growth of the statewide population. Fledgling-to-pair ratios at most sites increased relative to those in 1995, and terns nesting at several sites in 1996 were very successful. However, heavy predation at many San Diego County sites (including a majority of those with high pair numbers) and a local food shortage at Venice Beach compromised statewide fledgling production somewhat. Approximately 1981-2120 young terns fledged across the State, a record high and almost twice the number fledged in 1995; statewide F/P = 0.58-0.64. Most sites experienced increases over 1995 in the number of breeding pairs present, and several sites attracted more than 200 pairs. In 1996, 58% of the statewide papulation bred at only seven sites (NAS Alameda, Venice Beach, Huntington Beach, Santa Margarita River/North Beach, Mission Bay/FAA Island and Mariner's Point, Delta Beach/North), with the balance being distributed pretty evenly throughout the rest of the State. Almost half of the fledglings produced in the State came from only four sites; 45% of all potential new breeders produced this year fledged from NAS Alameda, Huntington Beach, Santa Margarita River/North Beach, and Delta Beach/North.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2010, with observers at 41 nesting sites providing data. An estimated 6437-6699 California least tern breeding pairs established 6968 nests and produced 1971-2245 fledglings at 51 documented locations. The fledgling to breeding pair ratio was 0.29-0.35. Statewide, 12,826 eggs were reported, with a Site Mean clutch size of 1.82 eggs per nest (St Dev = 0.198) and the Statewide clutch size of 1.84 eggs (St Dev = 0.441) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Pt. Mugu, Batiquitos Lagoon, Bolsa Chica Ecological Reserve and Huntington Beach represented 73% of the breeding pairs while Camp Pendleton, Huntington Beach, Alameda Point, Naval Base Coronado and Batiquitos Lagoon Ecological Reserve produced 68% of the fledglings. The 2010 chick mortality rate of 18% is slightly greater than the last two years. Seal Beach, North Island Maintenance and Training Facility (NIMAT), Camp Pendleton, and Naval Base Coronado represented 73% of the total reported chick deaths, but only 56% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2010 were gull-billed terns (Gelochelidon nilotica), common ravens (Corvus corax), coyotes (Canis latrans) and American crows (Corvus brachyrhynchos). Peregrine falcons (Falco peregrinus), great blue herons (Ardea herodias), common ravens, red-tailed hawks (Buteo jamaicensis), American crows, and western gulls (Larus occidentalis) were reported from the most sites. The monitoring effort of 2010 is scheduled to continue in 2011.

Monitoring to document breeding success of California least terns (Sterna antillarum browni) continued in 2004, with observers at 32 sites providing data. An estimated 6354-6805 California least tern breeding pairs established 7977 nests and produced 1351-1624 fledglings at 48 documented locations. The fledgling to breeding pair ratio was 0.20-0.26. Statewide, 12,774 eggs were reported, with a site average of 1.56 eggs per nest (St Dev = 0.248) and an average clutch size of 1.625 eggs (St Dev = 0.50) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, LA Harbor, Naval Base Coronado, Pt. Mugu and Batiquitos Lagoon represented 65% of the breeding pairs while LA Harbor, Alameda Pt., Pt. Mugu and Batiquitos Lagoon produced 70% of the fledglings. Three large sites (LA Harbor, Camp Pendleton and Batiquitos Lagoon) in southern California experienced high levels of chick mortality. Starvation was believed to be the cause of 33-57% death rate of chicks. The main predators of least tern chicks were coyotes (Canis latrans) and American crows (Corvus brachyrhynchos), accounting for up to 676 and 1022 deaths, respectively. Gulls (Larus sp.), peregrine falcons (Falco peregrinus) and American crows were reported from the most sites. The monitoring effort of 2004 is scheduled to continue in 2005.

In 1993, a minimum of 2,400 pairs of the endangered California least tern (Sterna antillarum browni) nested at 35 sites along the coast of California, and produced approximately 1848-2009 fledglings. This 14% increase over 1992 breeding population size continues the trend since 1987 of continued growth of the population, and is directly attributable to the efforts of people working on behalf of recovery of the species. The statewide total of 2,400 pairs is the highest number recorded since systematic monitoring began in 1973, and represents a four-fold increase over the estimated 600 pairs of that year. Predation on tern eggs, chicks, fledglings, and adults, and abandonment of eggs and chicks as a function of predation pressure, were the major causes of breeding failure in 1993. Monitors at 15 of 22 sites with low fledgling production (<0.9 fledglings/pair) attributed the lack of success to predation. The adverse effects of predation were manifested at all stages of breeding. Many types of human-related disturbance also constrained fledgling production in 1993. Breeding success and failure were strikingly localized; successful (>0.9 fledglings/pair) and unsuccessful sites were distributed throughout the State. Seven sites were particularly successful at fledging high numbers of tern chicks: NAS Alameda, Venice Beach, Seal Beach, Mission Bay/Mariner's Point, and Delta Beach North combined produced approximately 82% of the total fledglings produced statewide.

An estimated 4,141 to 4,182 pairs of California least terns nested at 39 nesting sites in 1998 and produced an estimated 2,686 to 2,810 fledglings. Statewide pair estimates increased 3.9%, but fledgling estimates decreased by 14.6% from 1997 estimates, likely due to high chick mortality at many sites. Seven sites (NAS Alameda, NAWS Point Mugu, Venice Beach, Huntington Beach, Santa Margarita River North Beach, Mariner's Point, and Delta Beach North) supported a combined total of 65% of statewide pairs and produced 66% of the state's fledglings in 1998. Fledglings per pair were 0.64 to 0.68, lower than 1997 (0.80). One of the more interesting findings of 1998 was a report of a nesting pair on evaporation pond dikes near Kettleman City in the San Joaquin Valley. Both eggs hatched and one chick apparently fledged. It is likely that monitors continue to underestimate renesting, as reported pair estimates are only 378 lower than statewide nest numbers of 4,541, despite 64 eggs lost to flooding, 900 observed dead chicks and minimum losses to predators of 147 eggs and 165 chicks. Another method of estimating pairs was requested and attempted by some monitors in 1998, based upon the number of renesters that a given site may generate, rather than the number of renesting pairs at that site. This estimate was 3,483 pairs, or 84% of estimates derived by the traditional method. Statewide mean clutch size was 1.66 eggs per nest, lower than for the previous three years, suggesting limitations in prey availability, as reported by several monitors. However, statewide mean hatching success was 0.80, similar to the previous two years. After a 54% increase in pairs and a 200% increase in fledglings between 1995 and 1997, pair numbers increased only 3.8% and fledgling numbers decreased by 14% from 1997. This is likely related to limitations in prey availability during 1998, as evidenced by high chick mortality, poor nest attendance, abnormal chick feeding and kleptoparasitism.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2014, with observers at 41 nesting sites providing data. An estimated 4232-5786 California least tern breeding pairs established 6038 nests and produced 2136-2859 fledglings at 48 documented locations across California. The fledgling to breeding pair ratio was 0.37 to 0.68. Statewide, 10,827 eggs were reported, with a Site Mean clutch size of 1.7 eggs per nest (St Dev=0.29) and a Statewide clutch size of 1.8 eggs (St Dev = 0.45) for Type 1 sites where monitors walk within the colony. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Huntington Beach, Point Mugu, and Batiquitos Lagoon represented 60% of the breeding pairs. Fledgling numbers were also unevenly distributed as the sites with at least 90 fledglings each (Camp Pendleton, Alameda, Batiquitos, Huntington Beach, Point Mugu, Naval Base Coronado, and Hayward), contributed 74% of the state’s production, and the sites with greater than 35 fledglings each (including the seven aforementioned sites plus Bolsa Chica, Venice Beach, Mariner’s Point, Napa Sonoma Marsh, and Oceano Dunes), contributed 90% of the state’s production. The 2014 statewide nonpredation chick mortality rate was 20%, similar to that in 2013 (22%). With the exceptions of Camp Pendleton and Naval Base Coronado, the larger nesting colonies experienced nonpredation chick mortality rates less than the average, similar to that documented in 2013. The predators known to be responsible for the greatest number of depredated least terns in 2014 were common ravens (Corvus corax), followed by American crows (Corvus brachyrhynchos), peregrine falcons (Falco peregrinus), coyotes (Canis latrans), gull species, western meadowlarks (Sturnella neglecta), unknown species, corvid species, raptor species, great horned owls (Bubo virginianus), northern harriers (Circus cyaneus), opossums (Didelphis virginiana), unknown avian species, and American kestrels (Falco sparverius). The monitoring effort of 2014 is scheduled to continue in 2015.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2009, with observers at 41 nesting sites providing data. An estimated 7130-7352 California least tern breeding pairs established 8037-8045 nests and produced 1734- 2132 fledglings at 51 documented locations. The fledgling to breeding pair ratio was 0.24-0.30. Statewide, 13,965 eggs were reported, with a Site Mean clutch size of 1.77 eggs per nest (St Dev = 0.110) and the Statewide clutch size of 1.76 eggs (St Dev = 0.455) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Batiquitos Lagoon, Pt. Mugu, and Huntington Beach represented 64% of the breeding pairs while Bolsa Chica Ecological Reserve, Alameda Point, and Batiquitos Lagoon Ecological Reserve produced 42% of the fledglings. The 2009 chick mortality rate of 15% is similar to the rate observed in 2004 (14%). LA Harbor, Camp Pendleton, and Batiquitos Lagoon Ecological Reserve represented 79% of the total reported chick deaths, but only 37% of the total chicks. The predators responsible for the greatest number of depredated least terns in 2009 were gull-billed terns (Gelochelidon nilotica) and American crows (Corvus brachyrhynchos). Gulls (Larus sp.), American crows, common ravens (Corvus corax), American kestrels (Falco sparverius), and peregrine falcons (Falco peregrinus) were reported from the most sites. The monitoring effort of 2009 is scheduled to continue in 2010.

Monitoring to document breeding success of California least terns (Sternula antillarum browni) continued in 2006, with observers at 31 nesting sites providing data. An estimated 7006-7293 California least tern breeding pairs established 8173 nests and produced 2571-3644 fledglings at 45 documented locations. The fledgling to breeding pair ratio was 0.35-0.52. Statewide, 12,698 eggs were reported, with a site average of 1.57 eggs per nest (St Dev = 0.257) and an average clutch size of 1.62 eggs (St Dev = 0.494) for Type 1 sites. Numbers of nesting least terns were not uniformly distributed across all sites. Camp Pendleton, Naval Base Coronado, Los Angeles Harbor and Batiquitos Lagoon represented 58% of the breeding pairs while Camp Pendleton, Los Angeles Harbor, Bolsa Chica Ecological Reserve, Batiquitos Lagoon Ecological Reserve and Venice Beach produced 68% of the fledglings. Only two sites, Camp Pendleton and Los Angeles Harbor, produced 40% of the statewide fledgling total. Four large sites (Alameda Point, Camp Pendleton, Los Angeles Harbor and Batiquitos Lagoon) experienced levels of chick mortality greater than the state average. Weather and food shortage are suggested causes of the 22-55% chick death rate. The main predators of least tern chicks were American crows (Corvus brachyrhynchos), coyotes (Canis latrans) and gulls (Larus sp.) accounting for up to 334, 222 and 157 deaths, respectively. American crows and common ravens were reported from the most sites. The monitoring effort of 2006 is scheduled to continue in 2007.

In 1995, a minimum of approximately 2,585-2,611 pairs of the endangered California least tern (Sterna antillarum browni) nested at 37 sites along the coast of California. This 7% decrease in breeding population size from 1994 brings to an end the trend since 1987 of continued growth of the population, and is likely attributable, at least in part, to the poor fledgling production experienced statewide in 1992. In addition to the drop in pair numbers, heavy predation pressure at many sites, an apparent shortage of food at two large sites, and a heavy storm in mid-June across the State, combined with a variety of human-related constraints on tern reproductive success, resulted in the lowest statewide fledgling-to-pair ratio recorded since fledgling production estimates were incorporated into monitoring protocol (1978). A minimum of approximately 963-1,174 fledglings was produced, 41% fewer than in 1994, resulting in a statewide fledgling per pair ratio of 0.37-0.45. As usual, successful and unsuccessful sites were distributed rather evenly throughout the State. Terns themselves were more unevenly distributed: 50% of the statewide population bred at only five sites (Venice Beach, Santa Margarita River/North Beach, Mission Bay/Mariner's Point and FAA Island, and Tijuana River/South); inclusion of an additional four sites (NAS Alameda, Bolsa Chica, Huntington Beach, and Delta Beach/North) accounted for 73% of all breeding pairs, and the inclusion of two more (Ormond Beach/Edison and Seal Beach) accounted for 81%. The fledglings produced at Santa Margarita River/North Beach, Mission Bay/Mariner's Point, and Delta Beach/North constituted 33% of the State total; the balance were distributed relatively evenly among sites.

From September 2013 to September 2015 SANDAG has provided funding to assist in the management and recovery of two federally listed species. Both the California Least Tern and Western Snowy Plover are listed species of birds who reside at D-Street during the breeding season of every year. While these species are primarily present only during the breeding season, managing the site is a year-round effort. USFWS and SDUPD manage the site in a somewhat artificial manner keying on the needs of these two species. The site itself is an artificial area created many years ago from the dredge spoils of the Sweetwater River as well as excess soil from Interstate 5 and State Route 54 construction activities. Funding provided allows us to continue managing the site.

Here we present information on the influence of vegetation growth, dune habitat, and enclosure fencing on nest site selection and productivity of California Least Terns (Least Terns) at the Venice Beach Colony, Marina Del Rey, California (colony). This study originated from a plan to use heavy equipment to flatten dunes and remove vegetation from the colony, and contradictory observations by project biologists that terns were mostly using those dunes for nesting, and nesting successfully. This study consisted of investigating both nest site selection by the terns and the productivity of those nests under several natural and manipulated treatments. However, heavy egg predation by the American Crow at this colony exerts a strong influence on nest placement and nest success. Our findings indicate that predation by American Crow exerts an "edge effect," with the heaviest predation on individuals away from the center of the colony and closest to the fence. We found that nests were less likely to succeed if they were placed within 20 m of the enclosure fence, in grids with fewer than 5 other nests (<125 nests/ha), more than 5 m from their nearest neighbor and more than 70 m from the center of the colony. Additionally, terns were more likely to be predated in areas with less than 5% vegetation cover, and prefer to nest, and are most successful, in areas with 20-40% vegetation cover. We found that the best vegetation management technique was to reduce vegetation to less than 30% cover, but even this was not as successful as areas that are naturally between 5-30% vegetation cover. The terns also prefer to nest, and are most successful in areas with dunes, although our finding indicate that predation increases with the number of dunes in an area. Based on these findings we recommend: 1. Manage the American Crow and other nest predators with a goal of decreasing the strong edge effect and colony failures. We must continue aggressive management to discourage incursions into the colony and use volunteer observers to inform staff of predation rates. 2. Nesting should be discouraged within 20 meters of the fence. 3. Control vegetation, with a goal of maintaining 20-40% cover in nesting areas within the colony. Vegetation manipulation will likely have the most impact if used to maintain open areas in the vegetated flat (Figure 2) and increase cover in the newly exposed areas (Figure 2). We should accomplish this by first removing non-nativ

The San Diego Bay National Wildlife Refuge protects a rich diversity of endangered, threatened, migratory, and native species and their habitats in the midst of a highly urbanized coastal environment. Nesting, foraging, and resting sites are managed for a diverse assembly of birds. Waterfowl and shorebirds over-winter or stop here to feed and rest as they migrate along the Pacific Flyway. Undisturbed expanses of cordgrass dominated salt marsh support sustainable populations of light-footed clapper rail. Enhanced and restored wetlands provide new, high quality habitat for fish, birds, and coastal salt marsh plants, such as the endangered salt marsh bird?s beak. Quiet nesting areas, buffered from adjacent urbanization, ensure the reproductive success of the threatened western snowy plover, endangered California least tern, and an array of ground nesting seabirds and shorebirds. The San Diego Bay National Wildlife Refuge also provides the public with the opportunity to observe birds and wildlife in their native habitats and to enjoy and connect with the natural environment. Informative environmental education and interpretation programs expand the public?s awareness of the richness of the wildlife resources of the Refuge. The Refuge serves as a haven for wildlife and the public to be treasured by this and future generations.

Over the course of this grant, San Diego Audubon staff, volunteers and partners carried out essential conservation and habitat restoration tasks to support nesting California least terns and MSCP-listed Nuttall’s Acmispon: conducting habitat management events at Mariner’s Point, North Fiesta Island, Stony Point, No Man’s Land and South Shores with thousands of volunteers; refining translocation protocols to establish and maintain a new population of Nuttall’s Acmispon in Mission Bay; supporting predator control efforts through our TernWatchers program to increase California least tern nesting productivity; carrying out research on alternative management efforts to reduce the reliance on herbicides; completing Annual and Long-term Management documents to guide continued nesting success in Mission Bay; engaging with the community about the importance of protecting the endangered California least tern; and supporting threatened sand dune habitat despite the challenges of a pandemic. This project was a success because of the thousands of hours of time donated by our dedicated volunteers, and the sustained support of our partners and other regional experts on California least tern management and invasive plant control. The management plans which were the final products of this grant will support permanent and visionary improvements to the coastal dune habitat in Mission Bay, creating benefits for the bay’s natural resources and the community members who enjoy and appreciate these resources. This project was partially funded by SANDAG TransNet EMP Land Management Grant #5005518

The California least tern (Sternula antillarum browni, least tern) is a federally endangered migratory seabird which nests on sandy beaches around San Diego Bay. Urbanization, habitat loss, and abundant predators have negatively impacted the population which now requires annual management and monitoring to protect the species from extinction. One of the largest remaining habitat areas for least terns is the D Street Fill, located in Chula Vista, California, which is an approximately 80-acre area of dredge spoils that provides sandy dune habitat with low-vegetation height for least terns to nest. The San Diego Unified Port District (Port) and the U.S. Fish and Wildlife Service (USFWS) jointly manage the site, which requires annual invasive plant removal, management and monitoring of the least tern seasonal breeding and nesting, and avian and predator control efforts.