Oil Pollution Impacts on Birds

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.

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:
ftp://ftpext.usgs.gov/pub/er/md/laurel/cwb_gulfcoast/