Breeding

Pair Formation

Begins when both birds arrive on territory. In Virginia, females arrive on territory of previous year as much as 3 wk before males, last week of Feb to first week of Mar (Baker and Cadman 1980). On Long Island, NY, birds arrive 17 Mar (B. Lauro pers. comm.). In Massachusetts, most birds arrive paired, last week of Mar to first week of Apr (RCH). Lone females defend territories until mates return or they pair with new mate (Baker and Cadman 1980, RCH).

Nest Building

See Behavior: sexual behavior. Nest-scraping begins as part of courtship, often several weeks before egg laying, performed by both sexes, most often by male. Several scrapes are made. “Decorative” items (bits of shell) are (rarely) brought to scrape from elsewhere.

First/Only Brood Per Season

Figure 5 . May lay repeat clutches if nests are destroyed or young depredated early. First clutches in Virginia, first week of Apr, peak mid-Apr. Second peak depends on timing of spring tides, as these can inundate and destroy all first clutches, and hence all renests occur at approximately the same time. Cold wet weather can result in less synchronous nesting in populations (Nol et al. 1984). First nest in New York by 1 Apr (B. Lauro pers. comm.). Massachusetts, most clutches complete by first week of May (RCH); peak hatch usually 27 d later. Chicks tended and fed until fledged, 35 d; begin feeding on their own, but still predominantly dependant on adults for food for some time; adults observed feeding young in late Aug, and possibly in Nov and Dec (Cadman 1980, J. Tuckwell pers. comm.). On islands near Puerto Rico, nesting in May and Jun (Raffaele 1989).

Selection

May make and abandon 5 or more scrapes (Tomkins 1954). In Georgia, may defend territory as much as 3 mo before eggs are laid (Tomkins 1954); more typically (Virginia) 6 wk (EN) and Massachusetts 1 mo (RCH).

Microhabitat/Site Characteristics

Non-randomly select nest sites with more substrate, less vegetation, farther from water, and higher elevation (Lauro and Burger 1989, RCH). Variability in habitats observed. In New York and Maryland, birds rarely nest in sand dunes, favouring marsh islands (Zaradusky 1985, Lauro and Burger 1989, D. Brinker pers. comm.). In N. Carolina and New Jersey, commonly nest on high, sandy sites (Bent 1929, Lauro and Burger 1989), only rarely on marsh islands (Shields and Parnell 1990). In Virginia, nest in dunes and salt marsh (Cadman 1979), dredge spoils, sometimes very close to high tide if nothing else available (EN). In Massachusetts, nest in low, flat sandy areas, upland dune, and marsh islands, the latter most frequently (RCH). Vegetative cover varies from non-existent or sparse in lower sandy areas, to moderate in marsh islands and dense in upland dunes vegetated with Spartina, Ammophila, Lathyrus, Solidago . Nests typically on slightly elevated site with at least 180° visibility, rarely on side-slopes with obstructed view (Bancroft 1927, Bent 1929, RCH). Elevation very important to nest success (Lauro and Burger 1989). Distance to water: high sites, average 7.5–12.7 m from water in New York and slightly further (21–32 m) in N. Carolina and Massachusetts (Lauro and Burger 1989, RCH). Vegetation averages 23–50% around nest sites, but highly variable (Lauro and Burger 1989, RCH). Distance to nearest conspecific nest depends on habitat, but average distance ranges from 124 to 190 m (RCH). Elevation above mean high tide: in New York, about 1 m above sea level, and significantly higher than random points (Lauro and Burger 1989). In Massachusetts, elevation depends on habitat, but all < about 0.3 m above sea level (RCH).

Construction

See Behavior: sexual behavior. Nests scraped during daylight hours. Actual scraping takes little time, bird settles on sand and scrapes shallow depression with feet. Once a pair has selected a scrape, lining is prepared by side-throwing in the vicinity and side-ways building at the site. Sometimes material carried to scrape in bill.

Structure And Composition

Nests typically a shallow depression scraped out of sandy substrate, often lined with shells or shell fragments, pebbles, or bits of tide wrack.

Dimensions

20 cm in diameter; 4–6 cm in depth.

Microclimate

No specific information. Nests in open areas with little cover or protection from elements. On Long Island, NY, often next to a small Solidago plant (B. Lauro pers. comm).

Maintenance Or Re-Use Of Nests, Alternate Nests

Nest scrape typically not re-used if nest is depredated or destroyed, but oystercatchers have been observed to repair nest and continue to incubate eggs after being washed over by tide and covered by wrack (RCH). Also will incubate eggs washed out of nests (RCH, EN). Scrape not re-used in subsequent years, except artificial structures or if few available sites on territory.

Nonbreeding Nests

Often several scrapes constructed in close proximity before one is chosen for nest.

Shape

Ovoid.

Size

Length (mm), breadth (mm), and volume (cc). Massachusetts, 56.8 ± 0.04 (SE), 39.1 ± 0.02, 40.2 ± 0.05, n = 126 (RCH); Virginia, 56.6 ± 0.12 (SE), 39.8 ± 0.05, 42.8 ± 0.15, n = 286 (Nol et al. 1984). Volume of eggs from Virginia were significantly higher than those from Massachusetts. Differences in the variation of egg size has been attributed, in part, to differences among females: larger females (using geometric mean of external body measurements) tending to lay more voluminous eggs (Nol et al. 1984). About 55% of the variation in egg size over 3 yr attributable to differences among females (Nol et al. 1984). Egg length more repeatable than egg breadth (Nol et al. 1984). In 3-egg clutches, the second egg is larger than the first and third, in 2-egg clutches the second is larger than the first (Nol et al. 1984, RCH). Incubation begins when the second egg is laid (see Behavior: self-maintenance), so the first is exposed to predation for a longer time. Eggs hatch in the order they are laid, the first 2 relatively synchronously, thus the resultant young may leave the nest before the third has hatched. Parents will attend to hatched young and may abandon the third egg. The second egg thus has the highest probability of survival (Nol et al. 1984).

Color

Buffy gray variably speckled with dark brown spots of various sizes. Spots usually more and larger at larger end of egg. Occasionally spotless or nearly so. Color consistent within individuals; can potentially distinguish eggs from different females (Lauro et al. 1992).

Surface Texture

Smooth.

Egg Laying

Clutch initiation probably not related to completion of nests as birds continue to dig and line scrapes after laying. Eggs laid average of 24–36 h apart, any time of day (RCH). Cold or wet weather may delay egg laying (Nol et al. 1984). Re-nesting usually takes place within 2 wk. Pairs with nearby feeding areas tend to lay earlier (Nol 1989). Parental behavior during egg laying includes incubation, copulation, and intense territory/mate defense.

Onset Of Broodiness And Incubation In Relation To Laying

Incubation normally begins after the second egg is laid.

Incubation Patches

On sides, not very edematous as in passerines.

Incubation Period

Normally 27 d (Bent 1929, Palmer 1967, RCH); 26 d in Virginia (EN); 28 d in Georgia (Tomkins 1954); 24–25 d in S. Carolina (Sprunt and Chamberlain 1949).

Parental Behavior

Both sexes incubate. Eggs are covered 100% of the time except during inter- or intraspecific distraction. Females incubate more than males (see Feeding: time budgets).

Hardiness Of Eggs

Eggs in nests washed over by spring or storm tides have successfully hatched (RCH). These washouts occur commonly but eggs not normally put back in nest (RCH).

Preliminary Events And Vocalizations

Tiny star-shaped fractures appear at large end of egg 2–3 d before hatching. Chicks vocalize in eggs (see Sounds). Distinct hole pipped one day or less before hatching.

Shell-Breaking And Emergence

Nest mates usually hatch within 24 h of each other, in the order they were laid. First and second eggs laid usually hatch more synchronously than third. Newly hatched chicks remain in nest several hours while drying. Earlier hatchlings will leave nest before remaining eggs hatch.

Parental Assistance And Disposal Of Eggshells

Parents fly away with eggshells and drop about 50 m from nest (RCH).

Condition At Hatching

Chicks precocial and downy (see description in Appearance, below). Mandibles of hatchlings hooked downward at tip, after 2–3 wk bill resembles that of plover; typical bill begins to develop at 4–5 wk. Average mass at hatching 37.3 g (± 4.25, n = 20; EN).

Growth And Development

Mass is the most variable measure during growth; varies substantially both within and among broods (Appendix 3). The length of the exposed bill, tarsus length, and middle toe, are all less variable, with little among-brood variance; that is, chicks of the same age all tend to have similar growth patterns for these body measurements (Appendix 3). Mass increases most rapidly, but linear measurements and mass asymptote at approximately 27 d. Growth follows a Gompertz curve for both linear measurements and mass (EN). Skull ossification continues beyond 2 yr (Cadman 1980).

Growth rates of chicks in different-sized broods also uniform: K = 0.14 in broods of one, two, and three chicks; adjusted asymptotes (Ricklefs 1967) were 400 g (n = 14 weights from 8 chicks), 400 g (n = 36 weights from 17 chicks), and 385 g (n = 70 weights from 24 chicks), respectively (Nol 1989).

Control Of Body Temperature

Precocial young; able to stand upright and run short distances within hours of hatching. Usually escape predators by hiding, particularly in first 10 d, but may run or swim (RCH). Escape diving has been observed (Hayes and Bennet 1985, RCH). First flights usually occur at 35 d.

Chicks respond to parent alarm calls by running for cover, then lying immobile. Often will not move until picked up. Within 1–2 d of all chicks hatching, parents and chicks move away from nest scrape. Young remain within nesting territory or move to feeding territory if nesting/feeding territories are adjacent. Chicks stay with adults and alternate between being fed and brooded when < 7 d.

Causes Of Death

Most juvenile mortality takes place prior to fledging (RCH). Oystercatcher chicks raised adjacent to a colony of Herring and Greater Black-backed gulls have been found dead as a result of a blow to the back of the head (RCH). Head wounds in one young observed near Black Skimmer colony (EN). Oystercatchers occupy areas susceptible to flooding and overwash by storm and spring tides, and they nest early in year. These facts suggest that exposure can be a significant cause of chick/egg mortality in this species. Predation—see Behavior: Social and interspecific.

Brooding

During the chick-rearing period the parents brood the chicks 7.9% and 3.1% of the time for females and males, respectively (females, n = 19; males, n = 23; not significantly different; Nol 1985). The time spent brooding chicks declines to almost 0 after 7 d (EN). Both adults feed young, but males feed young slightly more frequently than females do (1.44 vs. 1.14 trips/h, P = 0.054; Nol 1985). Internal motivation rather than past events (e.g., which sex took previous foraging trip), seems to trigger when a bird will leave on a trip to provision young (Nol 1985). Both adults frequently remain on territory, with brood foraging nearby (RCH). When nearby feeding areas are exposed by tide, non-tending adults will forage away from brood, while tending adult broods young or forages nearby, but frequently returns to feed young.

Feeding

Chicks almost entirely dependent on adults for food for at least 60 d after hatching (Palmer 1967, EN). Chicks typically follow adults as they feed. Chicks will forage on their own in dunes, presumably on small insects, but success rate unknown (EN). Adults will excise shellfish from shells, then deliver soft parts to young. Adults may feed long distances (1–2 km) from young, then carry whole food back (RCH, EN) or regurgitate it (Tomkins 1954). Average rates of provisioning young from hatching to fledging similar in broods of different sizes: one-chick broods, 2.0 trips/h (± 0.22, 6 pairs); two-chick broods, 1.8 trips/h (± 0.14, 9); three-chick broods, 1.6 trips/h (± 0.24, 7; Nol 1989).

Banded adults in Virginia have been observed feeding up to 3 of their own chicks plus 5 others, after chicks and parents dispersed from breeding territories onto common feeding areas, where territoriality was much less pronounced (EN). Juvenile birds appear to steal food from older birds (perhaps parents) on winter feeding grounds (Cadman 1980).

Several cooperative associations recorded: two mated pairs tended 1 nest in Texas (Chapman 1982). Communal nests attributed to 2 females and 1 male recorded in New York, and believed to be a consequence of high nesting densities (Lauro et al. 1992). In Massachusetts, in an area of high nesting density, 3 adults tended 2 nests 45 cm apart, with a total of 3 eggs (RCH); one additional nest tended by 3 adults, containing 5 eggs (first clutch), then 6 eggs (replacement clutch; Humphrey 1990). One nest attended by 3 adults containing 5 eggs in one year, 6 eggs in a second year, also reported in Maryland (D. Brinker pers. comm.).

Not known to occur. Occasional Common Tern egg in nest (EN).

Occurs within a few hours of hatching. Sustained flight (fledging) occurs at approximately 35 d (RCH). Family groups maintained through fall staging, migration departure (RCH), and on wintering grounds (up to 25 wk of age; Cadman 1980). See also: Parental care, above.

Juveniles migrate south with family groups. Small groups of nonbreeders, suspected to be 2 and 3 yr old birds, are frequently observed in the vicinity of breeding areas in Massachussetts throughout the breeding season; such birds often pair and may defend territory and make nest scrapes. Nonbreeding birds never observed near breeding territories in Virginia (EN).