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Shorebirds: East of the 105th Meridian


by
Brian A. Harrington
Manomet Observatory for Conservation Sciences
The North American group of shorebirds includes 48 kinds of sandpipers, plovers, and their allies, many of which live for most of the year in coastal marine habitats; others live principally in nonmarine habitats including grasslands, freshwater wetlands, and even second-growth woodlands. Most North American shorebirds are highly migratory, while others are weakly migratory, or even nonmigratory in some parts of their range. Here we discuss shorebirds east of the 105th meridian (roughly east of the Rocky Mountains). Historically, populations of many North American species were dramatically reduced by excessive gunning (Forbush 1912). Most populations recovered after the passage of the Migratory Bird Treaty Act of 1918, although some species never recovered and others have declined again.
High proportions of entire populations of shorebirds migrate by visiting one or a small number of "staging sites," areas where the birds accumulate fat to provide fuel before continuing with their long-distance, nonstop flights to the next site (Morrison and Harrington 1979; Senner and Howe 1984; Harrington et al. 1991). Growing evidence (Schneider and Harrington 1981) indicates that staging areas are unusually productive sites with highly predictable but seasonally ephemeral "blooms" of invertebrates, which shorebirds use for fattening. In some cases, especially for "obligate" coastal species, specific sites are traditionally used; even other species sites may shift between years. Because of this, conservationists believe some species are at risk through loss of strategic migration sites (Myers et al. 1987). Other species are threatened by the loss of breeding and wintering habitats (Page et al. 1991; Haig and Plissner 1993; B. Leachman and B. Osmundson, U.S. Fish and Wildlife Service, unpublished data).
The predicted consequences of global warming, such as sea-level change, will also strongly affect the intertidal marine habitats, which many species of shorebirds depend upon. Some of the strongest warming effects will be at high latitudes, including those where many shorebirds migrate to breed, as well as south temperate latitudes, where many of them winter.

Population Trend Data

Information on population trends in North American shorebirds comes largely from studies designed for other purposes, except in the case of a few species that breed within latitudes covered by the Breeding Bird Survey (BBS) and one game species, the American woodcock (Scolopax minor). We divide these studies into two types, those based on surveys during breeding and nonbreeding seasons.
Population trend data from breeding seasons come mostly from studies of declining or threatened species such as piping plovers (Charadrius melodus; Haig and Plissner 1993), mountain plovers (C. montanus; Graul and Webster 1976; F.L. Knopf, U.S. Fish and Wildlife Service, unpublished data), and snowy plovers (C. alexandrinus; Page et al. 1991). Additional data come from the BBS and from special survey efforts on game species such as American woodcock (Sauer and Bortner 1991).
Nonbreeding season data come mostly from aerial surveys of migrants on Delaware Bay during spring (Clark et al. 1993), of migrants by the International Shorebird Surveys (ISS) during spring and fall (Harrington et al. 1989), and by the Maritimes Shorebird Surveys (MSS) in eastern Canada during fall (Morrison et al. 1994). Although none of these projects was designed principally to gather data for population trend monitoring, they are the only data bases on migrant species that have been systematically compiled through a period of years. The Christmas Bird Counts are an exception; they are conducted when most shorebirds are south of the United States.
Largely voluntary efforts of the ISS of Manomet Observatory, the MSS of the Canadian Wildlife Service, the BBS of the National Biological Service, and surveys on Delaware Bay (DELBAY) coordinated by New Jersey and Delaware state wildlife agencies have produced rough data useful for trend analysis. Because the BBS is conducted during the breeding season and is based on roadside surveys, its value is greatest in analyzing population change of broadly distributed shorebirds common in temperate latitudes where survey effort is greatest. The ISS, MSS, and DELBAY projects have focused on migration season counts and, therefore, are the best (though not ideal) available resources for monitoring northern-breeding shorebirds, which include most species in North America.

Plovers
Three of the eight species of plover that regularly occur east of the 105th meridian (snowy plover, piping plover, and mountain plover) are species of concern (endangered, threatened, or candidate species); killdeer (C. vociferus) and perhaps black-bellied plover (Pluvialis squatarola) are in decline (Table). In North America, all of these except the black-bellied plover are distributed principally in temperate latitudes; snowy, piping, and mountain plovers breed in special, localized habitats (principally sandy beaches, salt lakes, and salt flats for snowy and piping plovers, short-grass prairie for mountain plovers). There has been no evaluation of trends for Wilson's plover (Charadrius wilsonia), typically a beach-nesting species in southern North America. There are no statistically significant population changes in American golden- (P. dominica) and semipalmated plovers (C. semipalmatus). Table. Species, major habitats, and population change in North American breeding shorebirds in the United States east of the 105th meridian.*
Scientific name Common name Habitat Reference and status Significance
Pluvialis squatarola Black-bellied plover Coastal a- d+ P < 0.10(a) ns(d)
P. dominica American golden-plover Upland d- ns
Charadrius alexandrinus Snowy plover Coastal g threatened  
C. wilsonia Wilson's plover Coastal unknown  
C. semipalmatus Semipalmated plover Mixed a- d+ ns(a) ns(d)
C. melodus Piping plover Coastal c threatened  
C. vociferus Killdeer Upland b- P < 0.05
C. montanus Mountain plover Upland b+ ns
Haematopus palliatus American oystercatcher Coastal unknown  
Himantopus mexicanus Black-necked stilt Fresh water b- ns
Recurvirostra americana American avocet Fresh water b- ns
Tringa melanoleuca Greater yellowlegs Mixed a- ns
T. flavipes Lesser yellowlegs Mixed a+ ns
T. solitaria Solitary sandpiper Fresh water unknown  
Catoptrophorus semipalmatus Willet Coastal a± b+ d- ns(a) ns(b) ns(d)
Actitis macularia Spotted sandpiper Fresh water b+ ns
Bartramia longicauda Upland sandpiper Upland b+ P < 0.05
Numenius phaeopus Whimbrel Coastal a- d+ P < 0.01(a) ns(d)
N. americanus Long-billed curlew Upland b- P < 0.05
Limosa haemastica Hudsonian godwit Coastal unknown  
L. fedoa Marbled godwit Mixed b+ ns
Arenaria interpres Ruddy turnstone Coastal a- d+ e- ns(a) ns(d) ns(e)
Calidris canutus Red knot Coastal a- d- e- ns(a) P < 0.10(d) ns(e)
C. alba Sanderling Coastal a- d- e- P < 0.01(a) ns(d) P < 0.01(e)
C. pusilla Semipalmated sandpiper Mixed a- d- e- ns(a) P < 0.02(d) P < 0.05(e)
C. mauri Western sandpiper Mixed unknown  
C. minutilla Least sandpiper Mixed a+ d- ns(a) P < 0.05(d)
C. fuscicollis White-rumped sandpiper Mixed unknown  
C. bairdii Baird's sandpiper Fresh water unknown  
C. melanotos Pectoral sandpiper Fresh water unknown  
C. maritima Purple sandpiper Coastal unknown  
C. alpina Dunlin Mixed d- e± ns(d) ns(e)
C. himantopus Stilt sandpiper Fresh water unknown  
Tryngites subruficollis Buff-breasted sandpiper Upland unknown  
Limnodromus griseus Short-billed dowitcher Coastal a- d- e+ P < 0.05(a) P < 0.08(d) P = 0.12(e)
L. scolopaceus Long-billed dowitcher Fresh water unknown  
Gallinago gallinago Common snipe Fresh water b- P < 0.05
Scolopax minor American woodcock Special b- f- P < 0.05(b) P < 0.05(f)
Phalaropus tricolor Wilson's phalarope Fresh water b- P < 0.05
P. lobatus Red-necked phalarope Special unknown  
P. fulicaria Red phalarope Special unknown  
* In the "reference and status" column and the "significance" column, "a" through "g" refer to a reference in footnote **. The reference footnotes also give the years the survey was conducted. If "+" follows the letter in the "reference and status" column, the population is increasing. If "-" follows the letter, the population is declining. In the "significance" column, "ns" means population increase or decrease is not significant. "P" is a measure of the confidence that the decline or increase is actually significant. A lower P value means there is more confidence that the trend is real. A population trend change at the P < 0.10 level is considered statistically significant.
** a Howe et al. (1989) for 1972-83.
 b B.G. Peterjohn, NBS, unpublished analysis, National Biological Service, Breeding Bird Survey, 1982-91.
 c Haig and Plissner 1993.
 d Morrison et al., in press 1974-91.
 e Clark et al. 1993 for 1986-92.
 f Sauer and Bortner 1991.
 g U. S. Fish and Wildlife Service, Office of Endangered Species, unpublished data.

Oystercatchers, Avocets, and Stilts
No significant population changes have been detected in the three species of these groups east of the 105th meridian (Table).

Sandpipers

This is the largest family of shorebirds. Five species of this family listed in the Table--willet (Catoptrophorus semipalmatus), upland sandpiper (Bartramia longicauda), long-billed curlew (Numenius americanus), marbled godwit (Limosa fedoa), and American woodcock-- commonly breed in the contiguous 48 United States. Two others, the long-billed curlew, which nest principally in short-grass prairie, and the American woodcock found in second-growth woodland, show significant population declines. Upland sandpipers (tall-grass habitats, including croplands) show a significant increase. The remaining sandpiper species breed principally north of the contiguous 48 states. Six of these--ruddy turnstone (Arenaria interpres), red knot (Calidris canutus), sanderling (C. alba), white-rumped sandpiper (C. fuscicollis), Baird's sandpiper (C. bairdii), and buff-breasted sandpiper (Tryngites subruficollis)--are principally high-latitude breeders; two (red knot and sanderling) of the three species for which trend analysis data are available are in decline (Table). The remaining species can be grouped as taiga or middle Arctic breeders; seven of these have not been evaluated for population trend change; five species--whimbrel (Numenius phaeopus), semipalmated sandpiper (Calidris pusilla), least sandpiper (C. minutilla), short-billed dowitcher (Limnodromus griseus), and common snipe (Gallinago gallinago)--were in significant decline (Table), and four species--greater and lesser yellowlegs (Tringa melanoleuca and T. flavipes), spotted sandpiper (Actitis macularia), and dunlin (C. alpina)--showed no significant change (Table). No species showed significantly increased population trends.

Phalaropes
Only one (Wilson's phalarope; Phalaropus tricolor) of the three species of North American phalaropes has been evaluated for population change, and it showed significant declines (Table).

Summary and Recommendations
Population trend evaluation has been conducted for 27 of 41 shorebird species common in the United States east of the 105th meridian. Of the 27 species for which trend data are available, 12 show no change, 1 increased, and 14 decreased (Table). There were no clear correlations with habitat.
It is important that shorebird populations are monitored nationally, yet most species are hard to monitor because they inhabit regions that are difficult to access for much of the year. Migration seasons appear to be the most practical time for monitoring most species. Unfortunately, sampling for population monitoring during nonbreeding seasons presents a group of unresolved analytical challenges. Additional work on existing data can help identify how or whether broad, voluntary, or professional networks can collect data that will better meet requirements for monitoring population change.
For further information:
Brian A. Harrington
Manomet Observatory for Conservation Sciences
Manomet, MA 02345
References
Clark, K.E., L.J. Niles, and J. Burger. 1993. Abundance and distribution of migrant shorebirds in Delaware Bay. Condor 95:69-705.

Forbush, E.H. 1912. Game birds, wild-fowl, and shore birds. Massachusetts State Board of Agriculture, Boston. 622 pp.

Graul, W.D., and L.E. Webster. 1976. Breeding status of the mountain plover. Condor 78:265-267.

Haig, S., and J.H. Plissner. 1993. Distribution and abundance of piping plovers: results and implications of the 1991 international census. Condor 95:145-156.

Harrington, B.A., F.J. Leeuwenberg, S. Lara Resende, R. McNeil, B.T. Thomas, J.S. Grear, and E.F. Martinez. 1991. Migration and mass change of white-rumped sandpipers in North and South America. Wilson Bull. 103:621-636.

Harrington, B.A., J.P. Myers, and J.S. Grear. 1989. Coastal refueling sites for global bird migrants. Pages 4293-4307 in O.T. Magoon, H. Converse, D.Miner, L.T. Tobin, and D. Clark, eds. Proceedings of the Sixth Symposium on Coastal and Ocean Management. American Society of Civil Engineers, New York.

Howe, M.A., P.H. Geissler, and B.A. Harrington. 1989. Population trends of North American shorebirds based on the International Shorebird Survey. Biological Conservation 49:185-200.

 Morrison, R.I.G., C. Downes, and B. Collins. 1994. Population trends of shorebirds on fall migration in eastern Canada, 1974-1991. Wilson Bull. 106. In press.

Morrison, R.I.G., and B.A. Harrington. 1979. Critical shorebird resources in James Bay and eastern North America. Pages 498-507 in Transactions of the 44th North American Wildlife and Natural Resources Conference. Wildlife Management Institute, Washington, DC.

Myers, J.P., R.I.G. Morrison, P.Z. Antas, B.A. Harrington, T.E. Lovejoy, M. Sallaberry, S.E. Senner, and A. Tarak. 1987. Conservation strategy for migratory species. American Scientist 75:19-26.

Page, G., L.E. Stenzel, W.D. Shuford, and C.R. Bruce. 1991. Distribution and abundance of the snowy plover on its western North American breeding grounds. Journal of Field Ornithology 62:245-255.

Sauer, J.R., and J.B. Bortner. 1991. Population trends from the American woodcock singing-ground survey, 1970-88. Journal of Wildlife Management 55:300-312.

Schneider, D.C., and B.A. Harrington. 1981. Timing of shorebird migration in relation to prey depletion. Auk 98:197-220.

Senner, S.E., and M.A. Howe. 1984. Conservation of Nearctic shorebirds. Pages 379-421 in J. Burger and B. Olla, eds. Shorebirds: breeding behavior and populations. Plenum Press, New York.


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