Demography and Populations

Age At First Breeding; Intervals Between Breeding

Individuals are believed not to breed until 3–4 yr of age (Tomkins 1954, Palmer 1967, Cadman 1980, Johnsgard 1981). Two year olds pair, court, defend territories, and excavate scrapes, but do not breed (Palmer 1967, RCH).

Clutch Size And Number Per Season

In Massachusetts, range: 1–6 eggs/nest; for monogamous pairs: 1–4, inclusive (RCH); mean clutch size: 2.81 (RCH); New York (including communal breeding associations with 5 or 6 eggs in some nests): 3.26 (Zaradusky 1985); Virginia: 2.33 overall (n = 281), first clutches: 2.78 (n = 129), second clutches: 2.30 (n = 61; Nol et al. 1984). In Massachusetts, 67% of first clutches contained 3 eggs (n = 49), 62% of second clutches contained 3 eggs (n = 8; RCH); in Virginia, 78% of first clutches with 3 eggs, 31% of second clutches with 3 eggs (Nol et al. 1984). Number of repeat clutches, usually one, depends on type and timing of destruction. Three repeat clutches reported (Nol et al. 1984). No relationship between food supply and clutch size (Nol 1989), at least within the range of food supply available in Virginia.

In Virginia, most replacement clutches contained 2 eggs (60%, n = 62) in early years of study (Nol et al. 1984), 3 eggs in later years (Nol 1989). This shift may represent changing age structure of the population, with older birds more likely to lay 3-egg replacement clutches (Nol 1989). In Argentina and the Galápagos, most clutches are 2 eggs (Nol 1984, A. J. Baker pers. comm.).

Egg Laying

Eggs laid at 1–2 d intervals (RCH). Most first clutches are synchronous within a 20 d period (Nol et al. 1984). Lost clutches are usually replaced within 2 wk (Baker and Cadman 1980, RCH).

Annual And Lifetime Reproductive Success

Nesting success (proportion of females that successfully hatch a clutch from first or second attempts): 72% (Massachusetts; RCH). Hatching success (eggs laid that hatched): Massachusetts 71% (RCH); New York 48% (Post and Raynor 1964). Fledging success (chicks hatched that fledge): Massachusetts, 34% (RCH); New York 54–80% (Zaradusky 1985), 36% (Post and Raynor 1964). Number of young raised to independence (for pairs that hatched ≥ 1 egg): range from 0 in 6 yr (7 pairs) to 5 in 3 yr (1 pair) (Virginia; Nol 1989). Mean percentage success for pairs that hatched at least 1 egg: 24.6% (SD = 30.5), or one successful nesting attempt every 4 yr (Nol 1989). Mean percentage success for all pairs in Virginia: 14.0%, SD = 19.7), or 1 successful attempt in 14 to 21 nesting attempts, based on 1 to 2 renests/yr (total number of nest years observed = 174; mea n = 4 yr/nest; Nol 1989). Population production (total number of young) in Virginia varied considerably from 0 (1984: 11 nests) and 3 (1979: 21 nests), to 17 (1982: 41 nests) and 20 (1983: 41 nests; Nol 1989).

Bird banded as breeding adult (thus assumed to be at least 3 yr old) in 1978, subsequently observed in 1992, so at least 17 yr old (EN). Second bird banded in same study area as a breeding adult, in 1981, observed in the winter of 1993, so a minimum of 16 yr old. One additional banded bird assumed to be at least 14 yr of age; birds living at least 10 yr appear to be common (EN).

Annual survivorship (based on return rates to study area, averaged over 5 yr; n = 30 for each sex) was 85% for both sexes (Nol 1985), but quite variable among years (range: 50% to 90%; Nol 1989). At least two birds moved to different, distant sites (> 1 km), however, so return rates underestimate survivorship (EN).

Avian cholera isolated from cultures of liver and heart of adult female found dead on Cape Romaine National Wildlife Refuge (S. Carolina); low levels of DDE found in tissues, not surprising for a mollusc eater (Blus et al. 1978). Poisoning from red tide possible for H. ater in Argentina (A. J. Baker pers. comm.), thus also for H. palliatus .

Natal Philopatry/Dispersal

No known cases of individuals breeding at their natal site. In Massachusetts, no bird banded as juvenile during a 3-yr study returned to natal site in 5 yr (RCH). In Virginia, no bird banded as chick since 1978 was observed breeding in study area (EN), but sample of banded chicks was small (< 30).

Breeding Site Fidelity/Dispersal

A pair that stays together typically nests in the same territory, although not necessarily in the same scrape, for a number of consecutive years (Tomkins 1954, EN, RCH). Immatures disperse from their natal site with parents in late summer. Birds from surrounding areas, and possibly farther away, form groups that may contain up to 100 individuals. These groups travel back and forth between different feeding areas, sometimes > 20 km (RCH).

Home Range

Pairs defend breeding territories that are often contiguous (Nol et al. 1984, RCH). Also defend feeding territories adjacent to breeding territories, separate from breeding territories, or may defend adjacent territories plus separate territories (Cadman 1979). Feeding territories not defended as vigorously because birds spend most of their time foraging. Feeding territories change in size with tide, thus often difficult to defend or define (EN). Feeding territories may be in excess of 1,600 m from breeding territories (RCH). Maximum distance observed travelling during breeding season in Massachusetts about 3 km (RCH).

Winter Site Fidelity

As the wintering range for the Atlantic population is fairly small, winter site fidelity is expected, but no information as yet.

Estimates Or Counts Of Density

Local in distribution from Massachusetts south to New York. Density varies with habitat quality, food availability, and extent of human disturbance. From New York south to Georgia, occupies favourable habitat in coastal areas. Density depends on habitat type, with higher densities occuring on dredge spoil islands in areas where humans occupy nearby mainland (sand) beaches (Cadman 1979, Leck 1984, Lauro and Burger 1989, Lauro et al. 1992). From Georgia south, including the Gulf Coast, distribution is local and sparse (Burleigh 1958, Degange 1978). Largest number of breeding pairs in Virginia (Table 1), on islands of the Virginia barrier islands reserve; this population increased by about 300 pairs 1986–1993 (EN). The number of breeding pairs in New York has doubled since 1986 (Humphrey 1990, Litwin et al. 1993). Earlier increases attributed to reduced hunting pressure and creation of sandy dredge spoil islands used for nesting (Zaradusky 1985).

Uncommon in Louisiana, confined to secluded coastal islands (Lowery 1974). In Alabama, uncommon breeder, permanent resident in coastal Mobile Co. (Imhof 1962). Considered a resident of Florida, where once common (Sprunt 1954), and Georgia since the first records were kept (Anon 1981). Listed as species of Special Concern in Florida (Kale et al. in prep.).

Winter Abundance

Analysis of Christmas Bird Count data estimate from a low of 1,106 (1972) to a high of 9,062 birds (1970). Since 1975, numbers have been less variable (range 1,134–3,558). Some winter population counts (particularly from Charleston, SC) were high in the late 1960s, but the total number of wintering birds appears to have stabilized around 2,000 individuals. The number of birds seen during Christmas Bird Counts does not appear to account for all breeding pairs, nor their offspring, as the total from Appendix 2 is about 3,180, or over 50% more than the total seen during mid-winter.

By mid-19th century, scarce throughout mid-Atlantic (see Distribution: historical changes). By 1930s, numbers had recovered in Virginia; by 1970s, relatively common up to New York. Presently (1994) the most common species of breeding shorebird in New York (B. Lauro pers. comm.), and very common in Virginia; also relatively common in New Jersey (Appendix 2). Uncommon to rare throughout West Coast and Gulf Coast, also Florida’s Atlantic coast.

Egg and chick predation, and storm and high tide wash out reduce breeding success (Johnsgard 1981, Nol et al. 1984, Lauro and Burger 1989). Nests on high ground most successful (Lauro and Burger 1989); in some locations high elevation nest sites appear to be limited, so pairs nest communally (Lauro et al. 1992). As communal nests are generally less successful, lack of nest sites probably limits population growth (EN). Habitat in New York and New Jersey appears to be saturated; high sites are generally occupied (B. Lauro pers. comm.). In Virginia, of 20 pairs that failed to hatch any eggs in any year (mean number of years observed = 3.1), 18 of these lost nests to high tides (Nol 1989). High nest site fidelity means that some pairs experience nest loss to high tides nearly every year.

Tomkins (1954), Post and Raynor (1964), and Zaradusky (1985) all cite interspecific competition as a limiting factor, although in Virginia and Long Island (NY) few pairs nest near other breeding species (EN; B. Lauro pers. comm; see Conservation: interspecific competition). At one location in Virginia, numbers stable for 11 yr (EN), but at another a sharp decline in breeders after inlet filled in, presumably because of less saltwater flushing of marshes and subsequent deteriorating effect on food (EN). Commercial oyster production has declined since 1984 (Virginia Marine Res. Comm, unpubl. rep.) in and around Chincoteague, VA, although numbers of wintering oystercatchers apparently remained stable from 1976 to 1992. In Florida, habitat loss and human disturbance have brought population declines (Kale et al. in prep.). In Baja California, collecting and human disturbance contributed to decline (Jehl 1985; see Distribution: historical changes).