Colonial Waterbirds in Galveston Bay

Galveston Bay serves as a major nesting area for many species of colonial waterbirds including herons, egrets, gulls, terns, pelicans, cormorants and others. Colonial waterbirds nest in colonies that range in size from just a few to thousands of nesting pairs. As the name implies, colonial waterbirds require aquatic habitats to complete their life cycle. They rely upon a plentiful food supply found in the open bay, mud flats, and seagrass beds. They also forage in estuarine and palustrine wetlands and in riparian habitats along the shores of local bayous.

Depending on the species, nests may be found in shrubs and trees or on the ground. Nesting sites are often in remote areas such as bird islands, stretches of beach, and riparian forests. The remote nature of nesting habitat helps to protect breeding adults and fledglings from predators and human disturbance. The nesting season in Galveston Bay is February through August.

The reproductive success of colonial waterbird populations is dependent upon the availability of suitable habitat free from disturbance. The following stressors have negative impacts on colonial waterbird populations in Galveston Bay:  

• Human disturbance of nesting sites, especially during nesting season
• Habitat loss:
  • Erosion of nesting islands due to dredging, vessel wakes, and loss of  shoreline vegetation
  • Subsidence of nesting habitat and conversion to open water
  • Loss of habitat due to conversion of land to human uses (development)
• Mortality of colonial waterbird hatchlings due to predation by red-imported fire ants, coyotes and other animals, and
• Bioaccumulation of contaminants ( e.g. DDT/DDE) in the food web.

About the Data

Data describing colonial waterbird populations for the Texas Coast are collected by volunteers on an annual basis and are maintained by the U.S. Fish and Wildlife Service Texas Colonial Waterbird Census. In 2008, the Galveston Bay Status and Trends Project analyzed the data for trends in colonial waterbird populations. The database contains nesting pair abundance for 31 species of colonial waterbirds observed at 132 nesting colonies in Galveston Bay during the years 1973-2006. The species for which data were collected are:

Species
1	American Oystercatcher	17	Least Tern
2	Anhinga	18	Little Blue Heron
3	Black Skimmer	19	Neotropic Cormorant
4	Black-crowned Night Heron	20	Olivaceous Cormorant
5	Brown Pelican	21	Reddish Egret
6	Caspian Tern	22	Roseate Spoonbill
7	Cattle Egret	23	Royal Tern
8	Double-crested Cormorant	24	Sandwich Tern
9	Forster's Tern	25	Snowy Egret
10	Fulvous Whistling Duck	26	Sooty Tern
11	Great Blue Heron	27	Tricolored Heron
12	Great Egret	28	White faced Ibis
13	Green Heron	29	White Ibis
14	Gull-billed Tern	30	White-faced Ibis
15	Laughing Gull	31	Yellow-crowned Night Heron
16	Least Bittern

Galveston Bay Colonial Nesting Waterbird Indicator

The indicator describing colonial waterbird nesting pair populations in Galveston Bay was initially created by the Galveston Bay Status and Trends project in 2005.The indicator below summarizes twenty-year trends (1987-2006) in population abundance for 16 species of colonial waterbirds grouped by feeding guild (marsh or open water feeders) and nesting habitat (tree or ground nesting species). Trends were identified as significantly decreasing or increasing (R² ≥ 0.5) or moderately decreasing or increasing (0.5 ≥ R² ≥ 0.25).  

Of the 16 species summarized by the indicator, significant declining trends in nesting pairs were found for black-crowed night heron and great blue heron. Moderately decreasing trends exist for tri-colored heron, white-faced ibis, reddish egret, laughing gull, and neotropic cormorant. A significantly increasing trend continues for brown pelican nesting pairs.  

Legend:

Visit these websites for more information about colonial waterbirds:

• US Fish and Wildlife Service - Texas Coastal Program
• NBII Central Southwest Gulf Coast Information Node (CSWGCIN)
• Great Texas Coastal Birding Trail
• Houston Audubon Society
• Audubon Texas
• Waterbird Conservation for the Americas
• Cornell lab of Ornithology - All About Birds