Status & Trends of North American Waterbirds

Killdeer
Howard B. Eskin
Killdeer

Waterbirds play an integral role as recyclers, predators, and prey in a variety of ecosystems, including many agricultural landscapes. They depend on aquatic habitats for at least some part of their lives, using the land as:

  • Habitat for feeding, resting, and roosting - and during periods of molt
  • Breeding grounds - with different types of habitats such as hedgerows, pastures, wetlands, and riparian areas, used for courtship, nesting, and the raising of offspring
  • Migratory stopovers - for critical resources during arduous journeys

Within North America, Audubon has identified 265 species of waterbirds that breed, winter, or migrate across the continental landscape. Of the 265 species, 215 (all but seabirds) potentially use farmland or "working lands" to some extent. Common waterbird species include:

  • Loons, grebes, pelicans, cormorants, herons, bitterns, egrets, ibises, rails, coots, gulls, terns, and skimmers
  • Waterfowl, such as geese and ducks
  • Shorebirds, such as oystercatchers, stilts, plovers, sandpipers, and phalaropes
  • Other species affiliated with water and wetland habitats, such as osprey and kingfishers
  • Several kinds of songbirds, including some species of flycatchers, swallows, warblers, sparrows, and blackbirds

There is a strong overlap between high-intensity row-crop agriculture and important regions for waterbirds in the central United States. Seven contiguous Bird Conservation Regions (BCRs) (11, 18, 19, 22, 23, 24, 26) - encompassing a broad swath of the central continental U.S. and constituting a large portion of the Mississippi watershed - devote more than 10 percent of their landcover to the production of row-crops (corn, cotton, rice, sorghum, soybeans, spring wheat, winter wheat, peanuts, tobacco).

Using 39-year datasets (1966-2004 inclusive) from the Breeding Bird Survey (BBS) and the Audubon Christmas Bird Count (CBC), researchers identified and determined the continental and regional population trends of 146 species of waterbirds that regularly occur in those seven targeted BCRs. Their findings are documented in Status and Trends of Waterbirds in High-Intensity Agricultural Areas of the United States.

Key findings include:

  • More waterbirds are showing long-term continental increases in population than decreases on one or a combination of the surveys.
  •     52 percent (71 spp) of the 137 species that regularly occur in the seven BCRs and for  which there is useful trend data are increasing.
  •     28 percent (39 spp) of the 137 species are decreasing.
  •     20 percent (27 spp) of the 137 species are stable.
  • Of the six subgroups of waterbirds (shorebirds, divers, gulls/terns/pelicans, waders, dabblers, others), all but shorebirds are increasing continentally.
  • Waterbirds tended to do better in the seven BCRs with the highest proportion of land devoted to row crops - increasing at a rate of 3.78 percent per year compared to 1.54 percent per year for the same suite of species overall on the continent.
  • All six subgroups of waterbirds are increasing in the region of high row-crop production (seven targeted BCRs).
  • Although there are more increasing species than decreasing both continentally and in the focal region of high row-crop production, there are nonetheless a significant number of declining species and additional species with inadequate trend information that are known to be of conservation concern.
  •     Four species of ducks in the focal area are of high continental priority because of their importance as game species.
  •     49 species of waterbirds appear on national or international lists of birds of conservation concern. However, a dozen of these waterbirds show trend increases sufficient to suggest they could be considered for delisting.
  •     16 species showed population declines sufficient to suggest they should be considered for possible addition to national or continental conservation concern lists.
  •     The greatest concern is for the species that have been declared globally threatened: Eskimo Curlew, Mountain Plover, Piping Plover, Long-billed Curlew, Buff-breasted Sandpiper, and Black Rail.

The analysis reveals that although current wetlands acreage is a fraction of what occurred 300 - even 100 - years ago, waterbird populations are showing a partial recovery, especially over the past 20 years. Probable contributors to this partial recovery include: 1) banning of organochlorine pesticides and the population recovery of fish-eating birds, 2) success of wetland and farmland conservation programs in restoring waterbird habitat 3) provision of excess food to waterbirds, especially corn and rice