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.
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.
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.
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 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 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 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.
