SUISUN BAY 139 SUISUN BAY 140 SUISUN BAY SUISUN BAY Located immediately downstream of the confluence of the Sacramento and San Joaquin Rivers, Suisun Bay is the largest contiguous wetland area in the San Francisco Bay region. Suisun Bay is a dynamic, transitional zone between the freshwater input of the Central Valley rivers and the tidal influence of the upper San Francisco Estuary. This area supports a substantial number of nesting herons and egrets, including three of the largest colonies in the region. Although suburban development is rampant along the nearby Interstate 80 corridor to the north, most of the Suisun Bay area is protected from heavy development by the California Department of Fish and Game and a number of private duck clubs. Black- Active Great crowned or year Site Blue Great Snowy Night- Cattle last # Colony Site Heron Egret Egret Heron Egret County active Page 501 Bohannon Solano Active 142 502 Campbell Ranch Solano Active 143 503 Cordelia Road Solano 1998 145 504 Gold Hill Solano Active 146 505 Green Valley Road Solano Active 148 506 Hidden Cove Solano Active 149 507 Joice Island Solano 1994 150 508 Joice Island Annex Solano Active 151 509 Sherman Lake Sacramento Active 152 510 Simmons Island Solano 1994 153 511 Spoonbill Solano Active 154 512 Tree Slough Solano Active 155 513 Volanti Solano Active 156 514 Wheeler Island Solano Active 157 SUISUN BAY 141 142 SUISUN BAY Bohannon Great Blue Herons and Great Egrets nest in a grove of eucalyptus trees on a levee in Cross Slough, about 1.8 km east of Beldons Landing. This site, on the property of a private duck club, is accessible only by boat and at high tide. Ownership: private Public observation areas: boat Latitude / Longitude: N 38.1827 / W 121.9565 Nest survivorship (± SE) Focal nest survivorship 1.0 Gr e a t B lue He r on 0.8 0.6 0.4 Gr e a t Egr e t 0.2 0 xxx xx xx x *n<10 1and993 n<50% ofxx total xx nests. = no data. Pre-fledging1 9brood94 sizexx ( xx 5 1995 xx xx 1996 xx xx 4 1997 xx xx Colony site description 1998 xx xxxxxx Topography: levee 3 1999 Length x width: 125 m x 60 m 2000 xx xx 2 2001 xx xx Nest substrate: 2002 branches) 1 ± xx SE) 2003 * Average nest height: 22 m 0 2004 Trees (dbh): not measured 2005 x x x xx xx xx xx xx xx xx xx xx xx Maximum tree canopy height:Eucalyptus 28 m x *n<101 9and91 n<50% of total nests. = no data. Vegetation cover: tree 60%, shrub 10%, Peak number199 2of active nests ground 10% 100 1993 sp. (live and dead 1994 80 1995 Evidence of disturbance 1996 Resident Red-tailed Ha 60 1997 a 1998 Possible disturbance sugg 40 1999 2000 (see references in Methods). 20 2001 2002 Land use 2003 * 0 2004 wk: potential source 2005 x Land use ested by published accounts 1991 = no data. 1992 Duck club 1993 1994 1995 Distance from colony site (m) a 1996 1997 xxxx 0- 1998 100 1999 100- X 2000 200 2001 200- X 2002 500 2003 500- 2004 X 2005 1000 X Campbell Ranch This colony site is located along Highway 113 about 17 km south of Dixon. Herons and egrets nest at two subsites separated by 123 m. Livestock graze within the colony. A motorbike track is 1 km from the colony. The closest sloughs from the Sacramento River are approximately 2 km to the east. Ownership: private Public observation areas: none Latitude / Longitude: N 38.2888 / W 121.8266 (West subsite) NestFocal survivorship nest survivorship (± SE) 1.0 0.8 Great Blue Heron SUISUN BAY 143 0.6 0.4 0.2 Gr e a t Egr e t 0 xxxx xx x *n<10 1and993 n<50% ofxx total xx nests. = no data Pre-fledging1 9brood94 sizexx ( xx 5 1995 * . 1996 ** NestFocal survivorship nest survivorship (± SE) 1.0 4 1997 xx 1998 0.8 3 1999 2000 0.6 Snowy Egret 2 2001 x 2002 0.4 1 ± SE) 2003 0.2 0 2004 *** 2005 ** 0 xx x *n<101 9and91 n<50% of total nests; = no data xxxxxxxxxxxxx 1992 Peak number of active nests x 200 1993 1 1993 = no data. 1994 . Pre-fledging1 9brood94 size ( 1995 * 1 1995 150 5 1996 1996 1997 xx 4 1997 100 1998 1999 1998 1 * n=1. 2000 3 1999 50 2001 2000 2002 2 2001 2003 2002 0 *1 ± 2004 SE) 2003 2005 0 2004 x 1991 = no data xxxxxxxxxxxx xx 2005 1992 1 x 1993 n=1.1991 = no data. 1994 . Peak number199 2of active nests 1995 50 1993 1996 1994 xxxx 1997 40 1995 1998 1996 1999 30 1997 2000 1998 2001 20 1999 2002 2000 2003 10 2001 1 2004 2002 2005 2003 0 ( 2004 continued 2005 x 1991 = no data. ) 1992 1993 1994 1995 1996 1997 x 1998 1999 2000 2001 2002 2003 2004 2005 144 SUISUN BAY Campbell Ranch (continued) Colony site description West subsite Topography: flood plain Length x width: 66 m x 61 m Nest substrate: Eucalyptus sp. (live and dead branches) Average nest height: 26 m Trees (dbh): 27 (50-100 cm), 4 (50-100 cm) Maximum tree canopy height: 34 m Vegetation cover: tree 21%, shrub 0%, ground 74% East subsite Topography: flood plain Length x width: 38 m x 5 m Nest substrate: Eucalyptus sp. (live and dead branches) Average nest height: 25 m Trees (dbh): 7 (50-100 cm), 1 (>150 cm) Maximum tree canopy height: 28 m Vegetation cover: tree 35%, shrub 0%, ground 18% Evidence of disturbance Swainson’s Hawk: behavioral response Red-tailed Hawk: behavioral response Human activity: behavioral response Some nest trees cut down during non-breeding season: potential sourcea Common Raven: potential sourcea a Possible disturbance suggested by published accounts (see references in Methods). Land use Distance from colony site (m) 0- 100- 200- 500- Land use 100 200 500 1000 Low density housing X X X Grazing X X X X Cordelia Road Great Blue Herons nested in a small stand of eucalyptus trees on the east side of Cordelia, on property owned by the Girl Scouts of America. Rapid development in recent years has changed Cordelia from a sleepy suburban village to a bustling commercial center. The seasonal edge of Suisun Marsh is 200 m east of the site. Ownership: private Public observation areas: Cordelia Road Latitude / Longitude: N 38.2123 / W 122.1313 NestFocal survivorship nest survivorship (± SE) 1.0 0.8 SUISUN BAY 145 Gr e a t B lue He r on 0.6 0.4 0.2 0 xxxx xxxxxxx 1 x n=1. 1993 = no data. Pre-fledging1 9brood94 size ( 5 1995 1 1996 4 1997 Colony site description 1998 Topography: hillside 3 1999 Length x width: 18 m x 12 m 2000 2 2001 Nest substrate: 2002 Average nest height: not measured 1 ± SE) 2003 Trees (dbh): 1 (100-150 cm) 0 2004 Maximum tree canopy height: 38 m 2005 xxxx xx xxxxxxx Vegetation cover: not measuredEucalyptus x 1991 = no data. 1992 Peak number of active nests Evidence of disturbance sp. 50 1993 1994 Human activity: potential source 40 1995 a 1996 Possible disturbance sugg 30 1997 (see references in Methods). 1998 20 1999 2000 Land use 10 2001 2002 2003 0 Land use ested by published accounts 2004 a xxxx 2005 Low density housing x Mid-density housing 1991 = no data. 1992 High density housing Distance from colony site (m) 1993 1994 0- 1995 100 1996 100- 1997 X 1998 200 200- 1999 X 2000 500 2001 X 500- 2002 1000 2003 X 2004 X 2005 X X 146 SUISUN BAY Gold Hill This heronry site is about 2 km south of Cordelia and 0.6 km east of Interstate 680, on the property of a farm equipment supplier. The surrounding habitat is mostly grassland and scrub brush to the west, with Suisun Marsh lying 0.5 km to the east. Ownership: private Public observation areas: none Latitude / Longitude: N 38.1917 / W 122.1289 NestFocal survivorship nest survivorship (± SE) 1.0 Gr e a t B lue He r on 0.8 0.6 0.4 0.2 Gr e a t Egr e t 0 x *n<10 1and993 n<50% of total nests. = no data Pre-fledging1 9brood94 size ( 5 1995 . Nest survivorship (± SE) 1996 Focal nest survivorship 1.0 4 1997 xxxxxxxx 1998 0.8 3 1999 * 2000 0.6 Snowy Egret 2 2001 2002 0.4 1 ± SE) 2003 0.2 0 2004 x 2005 0 x *n<101 9and91 n<50% of** total nests; = no data xxxxxxxxxxxxx 1992 111 Peak number of active nests x 150 1993 1993 = no data. 1994 . Pre-fledging1 9brood94 size ( 125 1995 1995 1996 5 100 1996 1997 xxxxxxxx ** 1997 1998 4 75 1999 1998 1 3 50 n=1. 2000 1999 2001 2000 25 2002 2 2001 2003 2002 0 1 ± 2004 SE) 2003 2005 0 2004 1991 xxxxxxxxxxxx xx 2005 1992 x 1993 1991 = no data. 1994 Peak number199 2of active nests 1995 50 1993 1996 1994 1997 40 1995 1998 1996 1999 30 1997 2000 1998 2001 20 1999 2002 2000 2003 10 2001 2004 2002 2005 2003 0 ( 2004 continued 2005 1991 ) 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 SUISUN BAY 147 Gold Hill (continued) Colony site description Topography: flood plain Length x width: 70 m x 16 m Nest substrate: Eucalyptus sp.(live and dead branches) Average nest height: 25 m Trees (dbh): 3 (100-150 cm) Maximum tree canopy height: 32 m Vegetation cover: tree 47%, shrub 0%, ground 69% Evidence of disturbance Human activity (extensive trimming of tree limbs in preseason): colony abandonment Resident Great Horned Owl: behavioral response Red-tailed Hawk: potential sourcea Human activity (heavy machinery): potential sourcea a Possible disturbance suggested by published accounts (see references in Methods).