Demography and Populations

Age At First Breeding; Intervals Between Breeding

In New York, 2 males, of 31 young marked, found breeding in same area: 1 at 2 and 1 at 3 yr of age (Wilcox 1980). In s. Alberta, of 102 chicks banded from 1995 to 1999, 2 found nesting in area to 2000: 1 male bred first at 3 yr (not seen in area prior to that year), 1 male first found on nest at 5 yr (seen in area in prior year only; CLG-T).

Clutch

Clutch size normally 4, rarely 3 eggs. At 227 nests in s. Alberta, mean clutch size 3.89 eggs ± 0.39 SD (range 2–5); mean clutch size of known renests: 3.82 eggs ± 0.60 (range 2–4, n = 11). In area of managed wetlands in s. Alberta, 39% (13 of 33) of pairs renested when nests destroyed in May, none (0 of 42) when clutch lost in Jun. Time between loss of clutch to laying of first egg varied from <4 to >15 d (CLG-T). Mean clutch size n.-central U.S. and s.-central Canada, from 1963 to 1991, 3.87 eggs (range 2–5, n = 80 nests; Kantrud and Higgins 1992).

Annual And Lifetime Reproductive Success

No estimate of lifetime reproductive success.

Western. Apparent success 52% and discrete Green estimator (estimate of Mayfield success) 31% in n.-central U.S. and s.-central Canada (n = 79; Kantrud and Higgins 1992). In s. Alberta, apparent nest success (percentage of nests in which ≥1 young hatched) highly variable among years: 25–64%, averaging 44% in area of managed wetlands (196 nests, 6 yr); 50–57%, averaging 52% in areas of unmanaged wetland basins (21 nests, 3 yr). Percentage of Mayfield nest success in managed area 3–43%; in unmanaged areas 12–37% (CLG-T). In N. Dakota, hatching success greater on native grasslands (70% of found-nests hatching eggs) compared to cultivated (33%; Higgins et al. 1979).

Of all nests lost in s. Alberta from 1995 to 1998, 98% (59 of 60) due to predation of eggs or adult, 2% (1 of 60) due to desertion. Of depredated nests, 46% (27) lining undisturbed, no egg fragments (unknown predator); 17% (10) very small egg fragments (unknown predator), 17% (10) punctured eggs (definite avian predator); 8% (5) large egg fragments (likely mammal); 5% (3) lining undisturbed, no shell fragments, 1 whole egg left (unknown predator), 3% (2) dead adult at nest, uneaten and very few obvious injuries (possibly avian), 2% (1) lining torn, no egg fragments (probable mammal), 2% (1) dirt in cup, no egg fragments (probable mammal; CLG-T). Of all nests lost in n.-central U.S. and s.-central Canada from 1963 to 1991 (n = 38), 5% of nests abandoned, 43% destroyed (44% mammalian predation, 6% avian, 29% unknown predation, 12% abandoned, 9% unknown fate; Kantrud and Higgins 1992).

Eastern. Reproductive success varies considerably between years depending upon abundance of predators. During 3-yr study at Wallops I., VA, 48 nests of 226 found survived to hatching (survival to hatching for each year, respectively, 1 of 66, 36 of 66, and 11 of 83), with most losses due to predation by raccoons, red foxes, feral dogs, and Fish Crows (Howe 1982). Productivity varies with number of extreme tides that occur during breeding period (Tompkins 1965, Howe 1982). Savannah River, GA, population produced only 11 chicks (from 16 nests) in 1962 (Tomkins 1965).

Number Of Broods Normally Reared Per Season

One brood (Tomkins 1965, Howe 1982).

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

For all previously banded adult females seen in study area in s. Alberta from 1996 to 1998, from 14 to 35% each year fledged ≥1 young/yr (mean 25%; n = 47 female-year); overall estimate of 0.48 fledged young produced/adult female/yr (CLG-T).

Annual adult survival rate: approximately 85% (Howe 1982). Return rates of breeding adults banded in s. Alberta from 1995 to 1998 suggested 88% survival 1 yr after banding; no difference between sexes (n = 58 females, 52 males). Program Mark analysis of these data (correcting for resighting probability) indicates annual adult survival estimate of 76–96%, depending on year (CLG-T). Survival from fledging to first year unknown.

Longevity record 10 yr 3 mo based on 33 recoveries of 2,058 Willets banded 1955–1998 (Klimkiewicz 1997).

Diseases

Staging fall migrants found dead in avian botulism outbreaks (bacterium Clostridium botulinum type C) in s. Canadian Prairies and N. Dakota. Willets made up 24 of 2,506 dead shorebirds collected at Pakowki Lake, Alberta, in 1998, and 2 of 290 in 1997 (Pybus and Anderson 1997, Peers et al. 1998); 2 of 513 at Lake Newall, Alberta, in 1925 (Munro 1927); 10 of 918 shorebirds at Whitewater Lake, Manitoba, in 1996, 9 of 202 in 1997, and 1 of 98 in 1998 (L. Strauman and R. Bazin unpubl.); 2 of 48 shorebirds at Old Wives Lake, Saskatchewan, in 1998 (K. Cash pers. comm.), unlisted numbers at Long Lake (Kidder Co.), ND (F. M. Uhler in Kalmbach 1934). Age of dead birds not determined. Botulism outbreaks recorded at greatly varying levels annually from s. Canada to Mexico (Kalmbach 1934). Importance as population-wide mortality factor unknown.

Body Parasites

Survey of intestinal helminth parasites identified 35 species of flukes (Trematoda; Platyhelminthes), 20 species of tapeworms (Cestoda; Platyhelminthes), 3 species of spiny-headed worms (Acanthocephala) and 4 species of round-worms (Nematoda) taken from 85 (Western) Willets collected from both breeding (46 from Alberta and Manitoba) and wintering (9 from California [see also Ching 1990] and 30 from Gulf Coast) distributions (Bush 1989). This survey summarized as follows: only 1 bird (chick <1 wk old) not infected; all others (including another <1-wk-old chick) with 3–15 species of helminths (median 7 species) with parasite density (number of helminths/Willet) averaged 518 individual helminths ± 87 SE (range 0–4,490, median 248, n = 85). Individual Willets collected in freshwater (breeding) habitats infected with on average 7.5 species of helminths ± 0.5 SE (range 0–15, median 7, n = 46), with mean parasite density 362 individuals ± 96 SE (range 0–3,901, median 173, n = 46); Willets collected in saltwater (wintering) habitats infected with 7.3 species ± 0.5 SE (range 4–14, median 6, n = 39), with mean parasite density 701 ± 149 SE (range 52–4,490, median 380, n = 39). Helminth fauna of breeding Willets included 14 species of flukes (3 species present in >20 of 46 Willets: Plagiorchis elegans, Notocotylus sp., Odhneria odhneri); 19 species of tapeworms (3 species present in >20 Willets: Anomotaenia n. sp., Anomotaenia gallinaginis, Aploparaxis sp.); 2 species of spiny-headed worms (Polymorphus marilis present in 23 of 46 Willets) and 2 species of roundworms (Capillaria spp.); helminth fauna of wintering Willets included 28 species of flukes (3 species present in >14 of 39 Willets: Odhneria odhneri, Maritrema patulus, Parvatrema sp.), 8 species of tapeworms (2 species present in >14 Willets: Anomotaenia n. sp., Ophreocotyle insignis), 2 species of spiny-headed worms, and 3 species of roundworms (1 species of Capillaria present in 29 of 39 Willets). New species of helminths found in intestines of Willets included Parvatrema borinquenae (mean intensity of 19.1 ± 12.9 SD from 14 Willets collected in Florida), P. bushi (mean intensity 5.0 ± 4.5 SD in 14 Florida Willets), and Paragymnophallus kinsellai (Bush 1989, Ching 1995).

Roundworm Skrjabinoclava inornatae (Nematoda) in 8 of 12 Western Willets (7 collected in Jan in Louisiana; 5 in Jun in Alberta; Wong et al. 1989); S. tupacinae and S. bakeri also found in Willets (Wong and Anderson 1990). The fluke Numeniotrema kinsellai found in both Western Willets taken in Jan from mudflats of Taylor Co., FL, but none of 19 Willets taken on sand substrates infected (Bush and Threlfall 1984). Two other species of flukes identified in Florida survey (MacInnis 1960). Willet host for adult microphallid fluke Levinseniella cf. cruzi for which other parts of life cycle includes snail Olivella biplicata as cercaria host and crab Emerita analoga as metacercaria host (Young 1938).

Ectoparasite American dog tick (Dermacentor variabilis; HDD).

Effects of these parasites on Willet survival unknown.

Exposure

Little information. Some nests lost due to high tides (Munro 1969, Tomkins 1965). Flooding chills embryos and also causes nest loss in S. Carolina (P. Wilkinson pers. comm.) and elsewhere along Atlantic seaboard (Tomkins 1965, Howe 1982).

Predation And Other

Some nesting losses of eggs or young due to predation by raccoon, possibly otter, gray rat snake, and unknown avian predator (Tomkins 1965, Munro 1969). Dead or badly injured Willet adults observed in s. Alberta from 1995 to 2000 included 8 males, 6 females, and 9 of unknown sex. Ten appeared killed or injured by predators, including 3 males and 1 of unknown sex killed at or near nest and not eaten (one of these by Swainson’s Hawk); 1 of unknown sex dead at nest and eaten; 2 females, 1 male, and 1 of unknown sex killed by predator away from nest and eaten; 1 male with wing sprain and unable to fly. Eleven injuries appeared to be from power-line impacts, including 2 males with broken wings and chest injuries, 3 females with broken wings, 1 male missing wing, 1 female with broken leg (lost the leg within month), and 4 of unknown sex with broken legs. Two of unknown sex found dead (and another barely able to fly) 1 wk after hailstorm in which at least 15 shorebirds and more than 100 ducks died (CLG-T). Willets die in botulism outbreaks in most years (see Disease and body parasites, above); importance of botulism, pesticides, and parasites in adult mortality unknown.

Competition With Other Species

No information.

Initial Dispersal From Natal Site

No information.

Natal Philopatry

On Long I., NY, 2 males (of total of 31 young banded) recaptured as nesting adults within 204 m and 365 m of their hatching spot (Wilcox 1980). In s.-central Saskatchewan, 1 chick (of 9 total banded) returned 3 successive years to site 5 km from where banded (Colwell and Oring 1989). In s. Alberta, 2 males (of 102 young banded) recaptured as nesting adults: only 1 with known hatch site, nested 3.4 km away (CLG-T).

Fidelity To Breeding Site And Winter Home Range

Little information. Eastern Willets exhibit strong fidelity to nesting and feeding territories (Tomkins 1965, Wilcox 1980, Howe 1982). For banded Willets from Long I., NY, returning birds (10 of 23) nested 30–112 m from previous year’s nest (Wilcox 1980). Former longevity record of this species (8-yr to 11-mo-old male [based on 26 recoveries of 1,701 Willets banded through 1981]) recovered at Shinnecock Bay, NY, in same 10' latitude-longitude block as banded by L. Wilcox (Clapp et al. 1982). All adult Western Willets banded at s.-central Saskatchewan site (4 males, 2 females) returned in year subsequent to banding (Colwell and Oring 1989). In area of managed wetlands, return rates of adults in year after marking in s. Alberta varied from 73 to 100% over 6 yr (69 males, 75 females). These birds nested median of 280 m (range 0–2,468, n = 65) from previous year’s nests (CLG-T).

Dispersal From Breeding Site

No information.

Home Range

Little information. At San Francisco Bay, CA, 40 patagial-tagged Western Willets habitually used same roosts and feeding areas; distance between roost and feeding about 1,000 m (Kelly and Cogswell 1979). At Lanark Reef, off Florida Panhandle during winter, median of 50 and 95% convex polygon home range estimates for 10 Willets were 0.26 km²(range 0.02–2.59) and 5.90 km²(range 2.36–65.88), respectively (Gunnels 1999).

Numbers

Recent estimates suggest total population of 250,000, with approximately 10% breeding in Canada (Morrison et al. 2001); Eastern sub-species estimated at 90,000 birds, Western at 160,000 (N. Warnock and R. I. G. Morrison pers. comm.). Total population number consists of estimates from wintering areas, including 5,200 eastern U.S., 52,300 central U.S., 70,000 Pacific, 29,800 Mexico, 4,400 Panama, 83,700 South America, for total of 245,400, of which 106,300 are on Pacific coastlines (Morrison et al. 2001, which lists all original count references). Breeding Bird Survey highest counts on specific routes (39.4 km long) 91.0 individuals (Sussex Co., DE), 62.0 (Cape May Co., NJ), and 42.6 (Siskiyou Co., CA; Price et al. 1995).

Western. Total population estimate for N. Dakota was 41,000 pairs in 1967; with highest densities of about 21 pairs/km²in northeast drift plains of the state; 35,000 pairs in 1992; 60,000 pairs in 1993 (Stewart and Kantrud 1972, Igl and Johnson 1997). In Utah, 10–15 breeding pairs found in fields surrounding the Barrens during mid-1970s (Sordahl 1981). In s. Alberta, actual nest densities from 1998 to 2000 in areas of managed wetlands (wetlands had water) averaged 1.5 nests/km²± 0.4 SD (n = 3 yr, 5 sites), in areas with natural wetland basins (dry through almost all breeding season in these years) averaged 1.0 nests/km²± 0.0 SD (n = 3 yr, 3 sites), in areas with no wetland basins averaged 0.3 nests/km²± 0.4 SD (n = 3 yr, 3 sites; CLG-T).

Eastern. For Maritime Provinces, atlas data used to estimate about 750 pairs with most (600 pairs) on Prince Edward I. (Erskine 1992). Census efforts in 1922–1925 estimated about 150 pairs (or 736 individuals) on Nova Scotia at end of breeding season; count included adults and assumed 3 young/pair (Tufts 1922, 1925).

A Massachusetts statewide census counted 37–39 pairs in 1984 (85–94 individuals); clustered at Monomoy NWR and Plum I., Parker River NWR (Melvin 1984). Although specifics are elusive, Massachusetts numbers much higher now, throughout coastal regions of the state (Veit and Petersen 1993, A. Poole pers. comm.). In e. Georgia, stable population of 100 pairs between Tybee I. and Bull River along U.S. Route 80 (Tomkins 1965). Willets were abundant nesters at Wallops I., VA (spring counts of 100–150 individuals) from 1970 through the early 1980s, but then declined (Vaughn 1993).

In the Bocaripo lagoon, ne. Venezuela, Willet numbers increase to 250 by end of Oct, and then vary between 150 and 220 until beginning of Mar (Rompré and McNeil 1994).

Trends

Breeding Bird Survey data show no long-term, statistically significant trends in Willet numbers for period 1966–1998, nor for periods 1966–1979 and 1980–1998 (Sauer et al. 1999). In N. Dakota, no significant change in numbers from 1967 to 1992–1993 (Igl and Johnson 1997).

No information. On northern prairies, Willet populations respond to changes in water levels. Locally, numbers seen to decline in response to drought or drier conditions at breeding sites (Ryan and Renken 1987, Gratto-Trevor 1999), but whether this results in population regulation on a broad scale is unknown.