San Diego Management & Monitoring Program


Library

Search

Filters


Results

2006 CALIFORNIA LEAST TERN BREEDING SURVEY 2005 Season report

Lead author: Dan Marschalek
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.

2009 CALIFORNIA LEAST TERN BREEDING SURVEY 2008 Season report

Lead author: Dan Marschalek
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.

2007 CALIFORNIA LEAST TERN BREEDING SURVEY 2006 Season report

Lead author: Dan Marschalek
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.

2010 CALIFORNIA LEAST TERN BREEDING SURVEY 2009 Season report

Lead author: Dan Marschalek
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.