Although the evidence is not yet ironclad, two recent reports support fears that populations of hundreds of bird species strongly dependent on water bodies are declining in much of the world.
In a study reported to be the first to provide detailed, long-term trend data over a substantial portion of North America, researchers have found that shorebird populations in the northeastern US and southeastern Canada have seen an average decline of about 2% per year for 20 years. The study was published in the January 2007 Journal of Avian Biology by a team of US and Canadian researchers (release  and article abstract ); for a copy of the full study, contact Jonathan Bart,  208-426-5216, or Stephen Brown,  508-224-6521.
The average population decline for 30 species during the 20 years was 36%, with about three-fourths of the species declining (and a few plummeting by 70-80%), and none increasing significantly.
In the central US - ranging from Texas to North Dakota to Ohio - there was no overall pattern for 29 species studied, though there were indications of increases and decreases for most species.
Limitations in the data lessen the ability of the researchers to make some firm conclusions about their findings. For instance, the trends, or lack thereof, could be caused by shifts in timing and location for migrating birds, not actual population declines. However, much of the evidence from the study, and from other studies, suggests there may indeed be significant population declines.
Elsewhere in the world, widespread declines have been documented in the report "Waterbird Population Estimates," released Jan. 22, 2007, by Wetlands International (release ).
The organization gathered data from about 15,000 observers working each year in more than 100 countries, and evaluated trends for 878 species that were divided into 2,305 populations. Each population is either a subspecies or a group of the same species that lives in a particular geographic area, such as a continent.
The most vulnerable waterbirds over the past five years have been in Asia, with 62% of the populations studied decreasing to some degree. The "best" situation was in North America, with 37% of populations studied decreasing. In between were Africa, Oceania, South America, and Europe.
The report - which spokesman Alex Kaat,  +31 65060 1917, says is not free for the media - updates a 2002 publication.
The data evaluated typically aren't as detailed or extensive as that used in the first study, and sometimes there are significant gaps. For instance, in Asia, there is no data on 60% of the populations. Nonetheless, the report is useful to many professionals, in part because it offers the best information available for some parts of the world.
The group concludes that the two biggest threats to waterbirds are habitat destruction, usually fueled by human developments, and climate change.
- Media coverage: Ireland On-Line, Jan. 23, 2007, "Waterbirds Pay Price of Global Warming." 
For more information on waterbirds in North America:
- South Atlantic Migratory Bird Initiative,  covering the south Atlantic and lower Mississippi Valley regions (some results available, others in process, some studies yet to begin).
- PRBO Conservation Science: Southern Pacific Shorebird Conservation Plan; Pacific Flyway Project  (older information, but possibly useful).
- Program for Regional and International Shorebird Monitoring (in early stages): USDA Forest Service  and ShorebirdWorld.org.