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Oil Pollution Impacts on Birds

Colonial waterbird sites, Gulf of Mexico

These colonial waterbird site maps were created using the Colonial Waterbird Database. Many waterbird colonies
are found on coastlines or coastal islands and are thus vulnerable to effects of the oil pollution at or near the coast.
Other types of wildlife are similarly vulnerable.
For broader information, see the USGS Response site.

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Oil extent: NOAA's Env.Satellite Data & Information Service's (NESDIS) daily composite. Metadata | Source.
Colonies: estimates of pairs, nesting adults, or related population parameters from multiple sources, mostly 1975 through ~2004.
NOTE: these data pre-date Hurricane Katrina, and much may have changed in coastal barrier islands in LA.
See "Sources" tab & "What is a colony?" tab for more information

    Unique colonies in database, by state
Species Texas Louisiana Mississippi Alabama Florida
American White Pelican 12 0 0 0 0
Anhinga 103 34 18 6 189
Black Skimmer 307 71 12 3 55
Black-crowned Night-Heron 155 60 6 1 101
Brown Pelican 15 21 0 1 89
Caspian Tern 112 6 1 1 1
Cattle Egret 288 57 29 44 282
Double-crested Cormorant 4 0 2 0 108
Forster's Tern 153 74 0 0 1
Glossy Ibis 1 0 0 1 55
Great Blue Heron 471 70 51 7 329
Great Egret 280 190 20 17 555
Great White Heron 0 0 0 0 86
Green Heron 8 4 1 7 31
Gull-billed Tern 204 9 2 1 7
Laughing Gull 239 42 0 0 44
Least Bittern 3 1 1 0 8
Least Tern 245 45 59 5 141
Little Blue Heron 232 103 27 42 315
Neotropic Cormorant 81 19 0 0 0
Reddish Egret 165 16 0 0 31
Roseate Spoonbill 138 23 0 0 57
Roseate Tern 0 0 0 0 14
Royal Tern 109 17 3 0 12
Sandwich Tern 92 15 3 0 6
Snowy Egret 276 147 13 7 216
Sooty Tern 29 2 0 0 0
Tricolored Heron 259 128 4 4 279
White Ibis 97 55 6 14 190
White-faced Ibis 92 9 0 0 0
Wood Stork 0 0 2 1 65
Yellow-crowned Night-Heron 42 21 6 3 31

While we pulled as many counts as we could find from the literature, it's possible
that not all known survey locations were captured in the database. Thus, AL and MS may
be underrepresented in this dataset.

What is a waterbird colony?

A waterbird colony may be a small area with 30 nesting herons, or a teeming site with thousands of
nests of herons, egrets, cormorants and ibises. Because colonies vary so much in size, methods for
counting or estimating their size vary greatly. In some cases, a simple count of
adults present can be a good index of how many birds are nesting (although you can still miss some),
but in larger colonies or in many cases where nests can be hidden or difficult to detect or count,
an estimate is recorded instead.

Here are some factors that make it hard to get an actual count (census) of birds in a colony:

  • differences in timing - not all birds nest synchronously
  • detection difficulty - birds do not always remain on their nests for survey, and many ground-nesters have cryptic nests/eggs
  • density - some terns, for example, nest so densely on the ground that photos and analysis of photos is needed
  • what is the best measure? - if productivity of a colony is what's important, then successful hatchings or fledglings may be what is estimated
  • methods vary - an aerial survey, versus a survey by boat or on foot can give different results

Thus "colony sizes" given on the map, and in the database behind it, are indexes of colony size
and not actual counts. They may have biases due to the above factors and others.

These data were collated by USGS Patuxent Wildlife Research Center (PWRC) from a number of
print and electronic sources through ~2003 (see the sources tab). We made a careful effort to record
what parameter was estimated. Below are some of the parameters. To make the maps on this site,
we simply aggregated the population size parameters into coarse groups. To work with the data
in more detail, see the Sources tab for download links.

Parameter estimated Units
breeding pop # of adults
breeding pop # of burrows
breeding pop # of burrows w/ at least indirect evidence of occu
breeding pop # of burrows with >= 1 adult
breeding pop # of burrows with >= 1 egg; chick; and/or adult
breeding pop # of nesting pairs
breeding pop # of nests; active
breeding pop # of nests; total
pop index # of adults
pop index # of burrows
pop index # of burrows w/ at least indirect evidence of occu
pop index # of burrows with >= 1 adult
pop index # of burrows with >= 1 egg; chick; and/or adult
pop index # of nesting pairs
pop index # of nests; active
pop index # of nests; total
total pop total # of birds
total pop unknown
total # of chicks chicks
total # of eggs eggs
total # of fledged young fledged young
total # of nesting pairs pairs
total # of nests nests
total # of nests with 1 or more chicks nests
total # of nests with 1 or more eggs nests
total # of nests with fledged young nests
arrival on colony date
departure of last adults date
departure of last fledge date
first egg observed date
first fledging date date
first hatching date date
first laying date date
last fledging date date
last hatching date date
last laying date date
mean fledging date date
mean hatching date date
mean laying date date
median fledging date date
median hatching date date
median laying date date
peak laying date date
unknown # of nests
unknown # of adults
presence/absence species not found
presence/absence species found

Data from the Colonial Waterbird Database

These data were collated by USGS Patuxent Wildlife Research Center (PWRC) from a number of
print and electronic sources through ~2003. Mapped data are generalized from a variety of parameters representing
'colony size': number of nests, number of pairs, number of adults, and so on.
For maps on this site, data were filtered/limited to data from TX, LA, MS, AL, & FL only.

These data do not include the most recent information after Hurricane Katrina; other birds such as shorebirds
are not included in this database.

All data from the database used in these maps may be downloaded through our FTP site here:

Year Title Type
N/A Colonial Bird Register Database
2004 South Florida Wading Bird Report 2004 Report
2003 Annual (1973-2003) Texas Colonial Waterbird Census. Report
2003 South Florida Wading Bird Report 2003 Report
2002 South Florida Wading Bird Report 2002 Report
2001 South Florida Wading Bird Report 2001 Report
2000 South Florida Wading Bird Report 2000 Report
2000 Summary of Breeding Roseate Terns in the Florida Keys: 1974-1998 Journal
1999 Mississippi Colonial Waterbird Count N/A
1999 Recent Breeding Status of Royal and Sandwich Terns in Northwest Florida Journal
1999 South Florida Wading Bird Report 1999 Report
1998 South Florida Wading Bird Report 1998 Report
1997 Distribution and Status of Least Tern Nesting Colonies in Southeast Florida Journal
1997 South Florida Wading Bird Report 1997 Report
1995 Data for Public Release: Interior Colonies Report
1991 Distribution and Abundance of Nesting Least Terns and Black Skimmers in Northwest Florida Journal
1991 Texas Colonial Waterbird Census Summary-1990 Report
1990 Atlas and Census of Wading Bird and Seabird Nesting Colonies in Louisiana 1990 Report
1990 Texas Colonial Waterbird Census Summary- 1989 Report
1989 Breeding Status of the Least Tern in the Florida Keys Journal
1986 Nesting Status and Colony Site Variability of Laughing Gulls in Southern Florida Journal
1985 Decreases in the Brown Pelican Population in Southern Florida Journal
1985 Status of the American White Pelican: an update Journal
1982 Florida atlas of breeding sites for herons and their allies: 1976-1978. Report
1970 Nesting Populations of Brown Pelicans in Florida Report
For data requests, please contact Mark Wimer,



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