Demography and Populations

Age At First Breeding; Intervals Between Breeding

Age at first breeding not known, probably 1–2 yr. First-year Short-billed Dowitchers frequently summer in small numbers south of breeding grounds, including South America (Suriname; Spaans 1978), Panama (Eisenmann 1951), Cuba (Barbour 1943), locally on both coasts of Mexico (Howell and Webb 1995), Atlantic Coast from Florida (Loftin 1962) to New Jersey (Jehl 1963), and Pacific Coast at Grays Harbor and Willapa Bay, WA, where first-year birds in Basic plumage and adults in Alternate plumage present (Paulson 1993). Summering individuals collected in Florida were sexually immature, had little or no fat, and most were in plumage of first-year dowitchers (Loftin 1962). Individuals summering in New Jersey had under-gone incomplete molts and were easily distinguished from postbreeding adults (Jehl 1963). No evidence of nonbreeding first-year dowitchers at Churchill, Manitoba (JRJ).

Clutch

Almost invariably 4. See Breeding: eggs, above

Annual And Lifetime Reproductive Success

At Churchill, in 1964–1967, hatching success was 100% of eggs (n = 30) and nests (n = 8; Jehl 1971); in 1992–1999, 9 of 16 nests successful, and in those nests, 35 or 36 eggs hatched (in exception, chick failed to emerge on time and was deserted). Fledging success ummeasurable.

Number Of Broods Normally Reared Per Season

One.

Longest documented life span 13 yr 3 mo (Klimkiewicz and Futcher 1989); one of similar age banded as second-year trapped and released 11 yr 1 mo later; 3 others, 8 yr 4 mo, 8 yr 1 mo, 7 yr 7 mo (data courtesy of Bird Banding Laboratory; BBL). By analogy to other similarly sized shorebirds, maximum expected about 20 yr (Marks et al. 1990). No data on survivorship.

Disease

Presumably susceptible to avian botulism (Type C), as 4 sick dowitchers (spp.) seen during outbreak at Delta Marsh, Manitoba, in 1964 (Manuwal 1967).

Body Parasites

Mallophaga Actornithophilus albus (Malcomson 1960). Five cestodes and 2 trematodes found in birds at Bristol Bay, AK, among them cestode Shipleya inermis was present in all 9 studied birds, Haploparaxis retroversa in 6 of 9 birds, and trematode Parorchis acassthus in 5 individuals. Large numbers of trematode Himasthla found by Didyk and Burt (1997). New species of cestode, Hymenolepis deblocki, in small intestine in 1 (Schmidt and Neiland 1968). Unidentified worm larvae found in gizzard of 1 of 19 Short-billed Dowitchers wintering in Texas (Wong and Anderson 1991).

In migration and winter, predation by raptors probably major cause (See Behavior: predation, above). Half of 42 birds reported to BBL were shot: 4 in North America, 3 in Central America, and 14 in South America. Dates: 2 in 1930s, 5 in 1960s, 7 in 1970s, 6 in 1980s, 1 in 1990s; optimistically interpreted, pattern suggests decrease in hunting pres-sure in last decade. Eleven other dowitchers killed by cats, cars, towers, obstruction, etc.

On breeding grounds (see Behavior: predation, above), various bird and mammal predators. In 1992–1999, 7 (of 16) nests failed from desertion or predation, including 1 adult killed on nest. Downy young vulnerable in prolonged periods of cold, wet weather (Jehl and Hussell 1966b).

Initial Dispersal From Natal Site

Initial dispersal distance probably depends on physiography, especially wetness of marsh. Records of broods moving 75–100 m from nest in first 24 h (JRJ).

Natal Philopatry

No data on distances dispersed between fledging and first breeding.

Fidelity To Breeding Site And Winter Home Range

One bird banded in Costa Rica recaptured there 2 yr later (Smith and Stiles 1979), indicating some fidelity to migratory stopovers or wintering sites; 1 second-year migrant banded on Gaspé Peninsula, Quebec, recaptured in same area 11 yr later. See also Behavior: spacing, above.

Dispersal From Breeding Site

No data.

Home Range

Not known. Adults in courtship flight may fly ≥2 km from nest, crossing territories of several other pairs. Feeding sites at Churchill may also be >2 km from nest areas (JRJ).

Estimates Or Counts Of Density

Total population size difficult to estimate, especially on west coast of Americas, where winter and migration distribution overlaps that of the Long-billed Dowitcher. Species population estimated at 150,000–175,000, based on following information and assumptions, which include our subjective assessments of habitat suitability.

Pacific Coast (L. g. caurinus). (1) Mean winter counts of dowitcher species on Pacific Coast of U.S., 1988–1995, 29,090 (Page et al. 1999). If 50%, Short-billed Dowitchers = 14,545.

(2) About 48,000 dowitchers winter along Baja California (Page et al. 1997), of which about 90% are thought to be Short-billed. Total 43,200.

(3) Counts in Sinaloa, Mexico, where 30% of shorebirds on Pacific coast of North America thought to winter, included 3,500 Short-billeds in Dec 1993 and 7,000 in Feb 1994 (Engilis et al. 1998). Average 5,300.

(4) A minimum of 3,100 winter in Panama, entirely on west coast (Morrison et al. 1998).

(5) Elsewhere on Pacific coast of South America, only about 1,500 (Morrison and Ross 1989; see below).

(6) Very few known or thought to winter else-where on west coast of Middle America. Allow 4,000.

Total 71,645. Most or all of these can be assumed to be caurinus, but see Paulson 1993 for cautions.

Spring censuses of dowitchers (both species, but predominantly Short-billed) along entire Pacific Coast of U.S. in Apr, when virtually the entire population of L. g. caurinus can be assumed to be north of Mexico but south of Canada) averaged 86,600; Page et al. 1999). The correspondence between winter and spring counts is striking. We estimate the current population of caurinus at 75,000.

Atlantic and Gulf Coasts (L. g. griseus and L. g. hendersoni). (1) Very large numbers of migrants (>100,000) pass through Suriname in spring and fall (Spaans 1978). However, that estimate >2 decades old. More recent data (Morrison and Ross 1989) indicated total dowitchers wintering in South America number about 49,000, with 97% (47,500) on north coast, 3% south on Pacific coast. Estimate 50,000.

(2) Totals from Christmas Bird Censuses (CBCs; 1998–1999) along Atlantic and Gulf Coasts of U.S. (N. Carolina–Florida–Texas) average 18,000.

(3) No indication that significant numbers winter on east coast of Middle America (see numbers for Panama, above). Allow 10,000.

(4) All Atlantic, Gulf Coast dowitchers can be assumed to be Short-billeds, as the number of Long-billeds wintering in this region is trivial.

Total (griseus + hendersoni) 78,000.

Only other estimate (North American Shorebird Conservation Plan, Final Draft Mar 2000; fide R. Gill) seems quite optimistic. It allows for 320,000 birds, including 150,000 caurinus, 60,000 hendersoni, and 110,000 griseus . Morrison et al. (1994b) estimate number of Canadian breeding dowitchers (i.e., griseus and hendersoni) at >100,000.

Despite species’ extensive breeding range, number of confirmed nesting areas few. Quebec: Confirmed only near Schefferville (Harris 1989). Labrador: Extreme northwest corner (54°40´ 10°N, 65°19´ 45°W; R. I. Goudie pers. comm.), Ontario (including James Bay): 2 nests (Winisk area; Tuck 1968, Soulliere 1993) although there are several other probable locations in the extreme northeast corner of the province (Harris 1987). Nunavut: Manning (1981) found nesting on N. Twin I. James Bay: also confirmed Akimiski Is. Manitoba: Known to nest only in immediate vicinity of Churchill (Jehl and Smith 1970, JRJ). Saskatchewan: Only 1 confirmed area (near Lake Athabasca), with 6 other probable areas in center of province (Smith 1996, C. S. Houston pers. comm.). Alberta: 3 confirmed sites in central Alta (Semenchuk 1992); also vicinity of Rochester, and 60 mi (97 km) north of Chipewyan (Prairie Nest Records, fide J. DuBois). British Columbia: “Breeds only in the vicinity of Chilkat Pass and St. Elias Mountains in extreme northwestern British Columbia, and at Masset on the Queen Charlotte Islands” (Campbell et al. 1990: 208). According to M. McNall (pers. comm.), the latter area (only 1 nest found) has recently been developed. Northwest Territories (excluding James Bay, see above): south shore Great Slave Lake (E. Kuyt, fide J. DuBois).

Local density evidently high (at least formerly) in central Alberta (Randall 1961), though not quantified. At treeline at Churchill, about 50 pairs in 7,000 ha (JRJ).

Trends

For much of nineteenth century, the Short-billed Dowitcher was an extremely common and much desired game bird. Given its enormous potential breeding area, the population could have numbered in the hundreds of thousands. M. Smith (quoted by Palmer 1949: 228) at Pine Point, Scarborough, ME, wrote of a spring flight of L. g. griseus on 25 May 1868 that “extended from horizon to horizon, and . . . lasted over three hours six miles out at sea . . . From where I [Smith] was [on land] the same sight presented itself. The body of birds must have been 12 or 15 miles wide and at least 100 long . . . [and] were in bunches from a dozen to several hundred, and were visible in all directions.” To the mid-1800s, dowitchers were common enough that Wilson could write of “eighty-five . . . taken at one discharge of the musket, and Audubon saw one hundred and twenty-seven killed by three barrels; and Frank Forester says that in his day [unstated] “a sportsman might fill a bushel basket with the proceeds of a day’s shooting on the beaches and marshes” (Forbush 1912: 19).

But its confiding nature and tendency to fly over shot flock-mates made it easy prey, so that by the late 1800s the formerly immense flocks were few and far between. In 1909, Forbush (1912: 258) “frequented the [coastal Massachusetts] haunts of this bird but saw only three during the summer.” The consensus was that it was “nearing extinction.” We have no direct information on the extent of market-hunting on the west coast.

Given protection, dowitchers rebounded, and were again common in the 1950s and 1960s. However, there are indications that this trend has been reversed, and that the species (at least on the East Coast) is perhaps only about half as common as several decades ago. ISS surveys from 1972 to 1983 indicated decline of 5.5%/yr, 46% overall (Howe et al. 1989). Similar rates continued through 1995–1997 at 6 sites in Massachusetts and Brigantine, NJ. Data from Maritimes (e. Canada) Shorebird Survey, 1974–1991 (Morrison et al. 1994 a), indicate significant decline, the rate dependent on type of analysis. Trends based on maximum size of migrating flocks mainly on Atlantic Coast also indicate declines (B. Harrington pers. comm.).

The mid-Atlantic Coast is the principal concentration point for spring dowitchers moving to breeding grounds either in central Canada (hendersoni) or Ungava (griseus). The largest flocks recorded by the ISS were 4,205 at Chincoteague, VA, 4,100 and 3,950 at Bombay Hook NWR, DE. In 1939, 8,000 counted at Jamaica Bay, NY; the highest recent counts there were 5,525 in 1983 and 2,100 in 1984.

At Churchill, dowitchers are reduced in some areas where they were common to abundant in the 1960s, but more common in others. Unknown if this reflects changes in habitat, population size, or local (northward) range shifts.

No data.