Colonial Waterbird Inventory and Monitoring ProgramEntry ID: BRDPWRC0008
Abstract: Since the demise of the Colonial Bird Register at Cornell University, no
national colonial waterbird population database currently exists. Planning is
underway (both in USGS, Biological Resources Division and the US Fish &
Wildlife Service (FWS)) to develop a monitoring program. Feedback on a data
form has been solicited from a number of states and many have responded. We ... now
have a set of "core fields" that have been agreed upon; these represent the
minimum set that is felt to be necessary to determine status and trends,
(1) colony site location and name,
(2) general nesting habitat description and use,
(3) census methods, and dates, and
(4) population size of each species.
Given the various types of software and hardware in use in different states,
the most effective way to centralize the data would be to have contributing
agencies provide an exported data file and description of the data fields. The
location of the centralized database is expected to be the Patuxent Wildlife
Research Center. The planning at this point includes an analysis by state,
region, and nation of each species, similar to what the Breeding Bird Survey
does annually. Of course, publication and privacy rights of the contributed
data will need to be addressed. We may use the Bird Banding Laboratory as a
model for this. RECOMMENDED PROTOCOL FOR A REGIONAL/NATIONAL COLONIAL WATERBIRD
INVENTORY & MONITORING PROGRAM
A number of meetings and workshops have been held in recent years to address
inventories of waterbirds and their habitats. With the initiation of the new
Biological Resources Division of USGS, a new emphasis is being placed on
inventory and monitoring of our national biological resources. Coupled with
this is a realization that, to be effective, partnerships among state, federal,
and non- governmental organizations (NGO) are necessary to complete these large
tasks. Because they are top carnivores in the food web and many species are
strongly tied to wetlands, waterbirds are consistently identified as an
important wildlife component to monitor. Wetlands are often identified at state
and federal levels as habitats that are in the greatest jeopardy.
There is a lot of regional and species variation in the timing of nesting.
In the north (ca. 36 N latitude), the nesting inventories should be focused
between 1 June and 25 June. In the south, this same period should also apply to
the ground-nesters, but for wading birds, at least two visits are probably
necessary, one in March, the other in late May-early June. In Florida, with
year-round nesting, 3-4 estimates may be necessary to include all species. If
at all possible, all colonies in the south should be visited at least twice.
Visits should be spaced at least a month apart.
Most agencies cannot afford a large-scale inventory of all colonies on an
annual basis. Given that, a number of alternatives are possible (see Erwin et
al. 1984 Proc. Workshop on Manage. of Nongame Species and Ecol. Commun., Univ.
of Kentucky). Assuming funding limitations. our recommendation is as follows:
1.Monitor ground-nesting species (gulls, terns, skimmers, cormorants,
pelicans) every 4 years. For species of special concern (endangered, etc.), the
major colonies should be censused annually.
2.Monitor tree-nesting (wading birds) every 4 years, the year following the
ground-nesting inventory. Annual counts for major colonies of selected species
(e.g. Wood Storks).
The scheduling should be kept consistent among regions to insure that
"metapopulations" are sampled at the same time. If schedules differ among
states, interpretation of trends over regions becomes problematic. For example,
some data exist to show that Roseate, Common and Least Terns move among
colonies in New York, Connecticut, and Massachusetts. Thus, New York (Long
Island) and southern New England states should form a regional unit when
censusing. Other areas form natural units, such as Chesapeake Bay (Maryland and
Virginia) and western Gulf of Mexico (Texas-Louisiana).
Focusing on coastal areas, starting with Great Lakes, Atlantic, Gulf and
West Coast, not Alaska.
Predominantly ground census methods used, limited aerial census methods.
papers have been published regarding census methods for seabirds, fewer for
wading birds. It is widely recognized that the total number of breeding pairs
at a colony in a given breeding season is the desired value to be estimated.
This value is often elusive because of the non-synchronous breeding of many
species at a colony (e.g., tropical populations are much more protracted than
are arctic populations in nesting), the crypticity of nests (e.g. crevices), or
sometimes simply the large size of the colony. The desire to achieve accuracy
may come at the cost of disturbance. Bibby et al. (1992, Bird Census
Techniques, Academic Press Ltd) for instance recommend plot sample methods but
caution investigators to limit visits to a tern colony to 20 min. We present
our recommendations for censusing various groups, keeping in mind that cost and
time are usually limiting factors for most states. Most of this information has
been published previously (Erwin 1979 USFWS/OBS publ., Erwin 1985 Trans. NE
Fish & Wildl. Conf.). 1.Alcids, petrels, and "true seabirds" - Because they are
represented in only a small number of states, the reader is referred directly
to Nettleship (1976), Birkhead and Nettleship (1980), and Bibby et al. (1992).
In most cases, monitoring small plots for nests is recommended, with densities
then extrapolated to the entire colony area to estimate breeding populations.
2.Gulls - Colonies can be located easily by fixed-wing aircraft and estimates
of small colonies (<300) can be made from the air where the habitat is fairly
open. For larger colonies, ground estimates can be made relatively rapidly by
having several counters flushing nesting birds while walking through the
colony. The total number of gulls estimated in the air can then be used as a
rough estimate of "nesting pairs" since, during the day, roughly one adult is
present per nest (Erwin l979). If more detailed data are desired at any
colonies, plots ranging to 20 X 20 m may be desirable, depending on the nest
density (Bibby et al. 1992). Mark-recapture methods (Lincoln-Peterson) can also
be used to estimate the accuracy of the nest counts (Erwin l979). 3.Cormorants
- Because they are black and produce a white guano background, cormorants can
be easily photographed from fixed wing aircraft with a 35 mm B&W film camera.
If aircraft are not available, conducting a ground count can be done either by
estimating numbers flushing from the ground (or trees), or by estimating the
number of birds after they land in the water near the colony. Because they fly
in lines, they are easier to estimate than many other seabirds. 4.Terns, Brown
Pelicans, and Black Skimmers - Some species such as the large Royal and
Sandwich Tern can be counted from aerial photos, along with skimmers. However,
not all sites are nesting colonies; sometimes skimmers roost on sites that
appear to be colonies from aircraft. Therefore, we recommend ground estimates
of large colonies (>200) and direct nest counts for smaller colonies. Because
the large terns and Brown Pelicans nest on the ground in the open, counts of
incubating birds can often be made from a vehicle or on foot using a scope.
This has the advantage of avoiding disturbance and egg loss to avian predators
such as Fish Crows. For the small and intermediate-size terns, we recommend
using the adult estimate as the estimated number of breeding pairs, since most
attempts to correlate numbers of nests and adults converge at about 1.0,
although there may be variation by time of day, season, or colony. For Least
Terns and Gull-billed Terns, colonies are usually small and nesting can often
be protracted through the season. Direct nest counts should be attempted and
2-3 visits may be necessary from June into July. Using the 1:1 adult to nest
ration usually still holds. Arguing over the appropriate "correction factors"
is probably a minor source of variation in the overall program. Consistency,
especially within each state, is the most important element in any monitoring
program. 5.Wading birds a. Great Blue Herons - Because they are so widespread,
they are a species being monitored at a number of locations. We recommend nest
counts from photographs in the early Spring before leaves come out in the
northern parts of the U.S. (early to mid-April). Ground counts can also be done
with more difficulty. Nest trees should be individually marked and numbers of
nests recorded. This should be done after the young begin to hatch, both to
help locate nests from the debris on the ground near the trees, and to reduce
disturbance at the site. b. Wood Storks - Because of their Endangered status,
effort should be made to estimate rather precisely the number of nests in a
colony. This can sometimes be done from fixed-wing aircraft, but usually ground
censuses are needed. Because storks depend on water level conditions, colonies
may shift; therefore, extensive surveying may be needed using a stratified
random survey design. Simply returning to previously-used sites may result in a
bias in trends. c. Mixed heronries of intermediate-sized herons - Most
heronries have several or more species. Because the eggs of many species are
indistinguishable, estimating exact numbers of nests can be difficult. We
recommend that, for small heronries (<100 nests), a nest count be attempted but
time limited to 30 min. To "assign" the nests to different species in a mixed
colony, estimate the number of each species flushing from the colony. For
larger colonies, we recommend that several censusers enter the colony to flush
birds, while 2 or more observers remain outside to estimate numbers by species.
It may be necessary to divide up the species by observer. We recommend
estimating Black-crowned Night-Herons and ibises first, since these are the
first to flush from the colony. On average, we estimate one adult equals one
nest for most wader species. 6.General Comments - If a state is so large that a
complete inventory cannot be achieved in a given year, it is best to conduct a
census of the large colonies at a minimum. Because some of the site dynamics
will be lost, we recommend that 2-3 other areas (e.g. counties) be thoroughly
censused to determine the degree of site turnover (Erwin et al. 1984, Erwin
1985). These could even be done in years other than the one devoted to the
large-colony effort. The comment highlighted above under Wood Storks needs to
be reiterated: simply returning year after year to previously occupied sites
leads to a dangerous bias. A carefully developed survey is needed to identify
new sites that may develop as well as revisiting old sites.
Purpose: 1. Regulatory agencies need to have data on colony or roost site locations
and feeding areas to assist them in making decisions about protection and/or
2. State, Federal, and NGO groups need to know status and trends of selected
populations of waterbirds at local, regional, and national scales.
3. Waterbird monitoring may provide useful "bioindication" of changes in
wetland habitats over time
4. Waterbirds are an important recreational resource (e.g. bird watchers)
are often used as symbols for conservation (e.g., National Audubon Society
logo, Maryland's Chesapeake Bay commemorative license plate). Thus, their
status is often quite conspicuous.
(Click for Interactive Map)
Data Set Citation
Dataset Originator/Creator: Patuxent Wildlife Research Center Inventory and Monitoring Biological Resources Division U.S. Geological Survey ;
Dataset Title: Colonial Waterbird Inventory and Monitoring Program
Dataset Release Date: 1997
Dataset Release Place: Laurel, MD
Dataset Publisher: Patuxent Wildlife Research Center, USGSOnline Resource: http://www.pwrc.usgs.gov/cwb/
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Creation and Review Dates
DIF Creation Date: 2004-03-16
Last DIF Revision Date: 2005-04-19