Breeding

Author: Tom Virzi (TV), Dept. Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ.

Pair Formation

Pair formation begins when both birds arrive on territory. In Georgia and Texas, resident pairs begin to defend territories in January (B. Winn, S. Heath, unpublished). In South Carolina resident pairs seen on territory every month of the year except October (Sanders et al. 2004). 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). In New Jersey, individuals arrive early-Mar and pairs form by late-Mar (TV). In New York, birds arrive mid-Mar (B. Lauro, unpublished). In Massachusetts, most birds arrive paired, last week of Mar to first week of Apr (RH). Lone females defend territories until mates return or they pair with new mate (Baker and Cadman 1980, RH). On islands near Puerto Rico, nesting in May and Jun (Raffaele 1989). On Galapagos Islands, nesting in late December, early Jan (EN).

Nest Building

See Behavior. Nest-scraping begins as part of courtship, often several weeks before egg laying, performed by both sexes, most often by male. In Georgia, may defend territory as much as 3 mo before eggs are laid (Tomkins 1954); in Virginia, more typically 6 wk (EN), New Jersey and Massachusetts 1 mo (TV, RH).

First/Only Brood Per Season

Figure 5. Typically lay repeat clutches when nests are destroyed or young depredated early; in South Carolina, 67% had 2 nest attempts and 35% had 3–4 nests (Thibault 2008); up to 6 nest attempts reported in New Jersey (TV). Earliest full clutch reported in Texas Jan 22 (Hockey and Freeman 2003). 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 most renests occur at approximately the same time. Cold wet weather can result in less synchronous nesting in populations (Nol et al. 1984). In New Jersey, earliest nest reported on 6 Apr (TV) and peak nest initiation late-Apr to May (Virzi 2010a). First nest in New York by 1 Apr (B. Lauro, unpublished). In Massachusetts, earliest nest 25 Mar; mean initiation date 29 Apr (Murphy 2010). Further south, first clutches initiated earlier; South Carolina, first nest 3 Mar (Sanders et al. 2008); Georgia peak nest initiation 4 Apr (B. Winn, unpublished); Florida mean nest initiation 10 Apr (Toland 1999).

Peak hatch usually 27 d later. Chicks tended and fed until fledged, approximately 35 d; begin feeding on their own, but still predominantly dependent on adults for food for some time; adults observed feeding young near breeding sites in late-Aug in New Jersey, and in Dec after migrating to Florida (TV).

Microhabitat/Site Characteristics

Non-randomly select nest sites with more substrate, less vegetation, farther from water, and higher elevation (Lauro and Burger 1989, RH). In New York, New Jersey and Maryland, birds rarely nest in sand dunes, favoring marsh islands (Zaradusky 1985, Lauro and Burger 1989, Virzi 2008). In North Carolina and New Jersey, commonly nest on high, sandy sites (Bent 1929, Lauro and Burger 1989); also often use tide wrack deposits for nesting in New Jersey salt marshes, sandy sites preferred, and vegetated sites on dredge-spoil islands (Virzi 2008). In Georgia and South Carolina, oyster shell mounds in back-bay areas used extensively (Winn 2000, Sanders et al. 2008). In Virginia, nest in dunes and salt marsh (Cadman 1979), dredge spoils, sometimes very close to high tide if nothing else available (Wilke et al. 2005). In Massachusetts, nest in low, flat sandy areas, upland dune, and marsh islands, the latter most frequently (RH). 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, and Solidago. Nests typically on slightly elevated site with at least 180° visibility, rarely on side-slopes with obstructed view (Bancroft 1927, Bent 1929, RH).Elevation very important to nest success (Lauro and Burger 1989, Virzi 2008). Distance to water: high sites, average 7.5–12.7 m from water in New York and slightly further (21–32 m) in North Carolina and Massachusetts (Lauro and Burger 1989, RH). Vegetation averages 23–50% around nest sites, but highly variable (Lauro and Burger 1989, RH). Distance to nearest conspecific nest depends on habitat; in South Carolina, mean distance 334 m ± 27 (SE) all habitats; 200 m ± 29 (SE) barrier islands; 65 m ± 10 (SE) estuarine islands; 577 m ± 51 (SE) edge shell mounds (Sanders et al. 2008). Elsewhere, average distance ranges from 124 to 190 m (RH); may be much lower (< 10 m) on small back-bay islands with high pair density in New Jersey (TV). 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 (RH).

Nest Construction

Nests scraped during daylight hours. Actual scraping takes little time; bird settles on sand and scrapes shallow depression with feet. May make and abandon multiple scrapes (Tomkins 1954). Once a pair has selected a scrape, lining is prepared by side-throwing in the vicinity and side-ways building at the site.

Nest Structure and Composition

Nests typically a shallow depression scraped out of sandy substrate, sometimes lined with shells or shell fragments, pebbles, bits of tide wrack, or other debris. In New York and New Jersey, sand substrate preferred; however, tide wrack also used extensively in marsh habitat (Lauro and Burger 1989, Virzi 2008). In Virginia and South Carolina, shell rake used predominantly in seaside marshes (Wilke et al. 2005, Sanders et al. 2008); shell rake used extensively in Georgia and Texas as well (Winn 2000, S. Heath, unpublished).

Nest Dimensions

20 cm in diameter; 4–6 cm in depth.

Nest 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, unpublished). In New Jersey, often place nests beneath Iva frutescens shrubs and in dense Phragmites australis where nests are well-shaded (TV).

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 (RH, TV). Also will incubate eggs washed out of nests (RH, EN). Scrape usually not re-used in subsequent years, except artificial structures or if few available sites on territory. In Virginia, nests often found in same spot as previous year – both at sites with limited and apparently adequate space. Scrapes assumed to be re-made, but location is sometimes exact as indicated by markers from previous year (AW).

Egg Shape and Size

Ovoid. Length (mm), breadth (mm), and volume (cc). South Carolina, 56.2 ± 0.3 (SE), 39.2 ± 0.2 (SE), volume not available, n = 114 (Sanders et al. 2008); Virginia, 56.6 ± 0.12 (SE), 39.8 ± 0.05, 42.8 ± 0.15, n = 286 (Nol et al. 1984); Massachusetts, 56.8 ± 0.04 (SE), 39.1 ± 0.02, 40.2 ± 0.05, n = 126 (RH). Volume of eggs from Virginia was significantly higher than those from Massachusetts. Differences in the variation of egg size have been attributed, in part, to differences among females: larger females (using geometric mean of external body measurements) tending to lay more voluminous eggs. About 55% of the variation in egg size over 3 yr attributable to differences among females. Egg length more repeatable than egg breadth. 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, RH). Incubation begins when the second egg is laid, so the first is exposed to predation for a longer time.

Egg 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. Eggs in replacement clutches late in season often spotless and sometimes bluish in color (TV).

Egg 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 (RH). Cold or wet weather may delay egg laying (Nol et al. 1984). Pairs with nearby feeding areas tend to lay earlier (Nol 1989). Parental behavior during egg laying includes incubation, copulation, and intense territory/mate defense. If nest fails, replacement clutches laid after 14 d in Virginia (Nol 1989); after 19 d in Massachusetts (Murphy 2010). In South Carolina, replacement clutches laid as soon as 6 d (Thibault 2008). Eggs laid at 1–2 d intervals (CM). Most first clutches are synchronous within a 20 d period (Nol et al. 1984). Lost clutches are usually replaced within 2 weeks (Baker and Cadman 1980, CM).

Clutch Size

Full clutch is typically 3 eggs. In Florida, mean clutch size 2.7 eggs (Toland 1999); Georgia 2.5 eggs (Sabine et al. 2006); South Carolina 2.5 eggs (Sanders et al. 2008); Virginia 2.8 eggs (Nol et al. 1984); New Jersey 2.3 eggs (TV); New York 3.3 eggs (Post and Raynor 1964); Massachusetts 2.8 eggs (Murphy 2010).

Replacement clutches more likely to be smaller than first clutches (Thibault 2008); in Florida, mean second clutch size 2.2 eggs (Toland 1999); Virginia 2.4 eggs (Nol et al. 1984); New Jersey 2.1 eggs (TV); Massachusetts 2.3 eggs (Murphy 2010). Later clutches often only 1 egg (TV). See Demography and Populations section for additional information on clutch sizes and number of clutches per season.

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, Davis et al. 2001); 28–29 d in Georgia (Tomkins 1954, Sabine et al. 2006); 24–25 d in S. Carolina (Sprunt and Chamberlain 1949); 26 d in Virginia (EN); 28 d in New Jersey (Virzi 2008).

Parental Behavior

See Behavior: Daily Time Budget. Both sexes incubate, however females incubate more than males. In North Carolina, eggs were incubated 90% of the time at undisturbed nests (McGowan and Simons 2006). Human disturbance (ATV traffic) was negatively correlated with time spent incubating in North Carolina (McGowan and Simons 2006); South Carolina, pedestrian activity reduced time spent incubating (Sabine et al. 2008); New Jersey, both human disturbance and predation pressure reduced incubation times (TV). Human disturbance also increases number of trips to/from nest; undisturbed 2.25 ± 0.60 trips/hr; disturbed 3.66 ± 0.17 trips per hour; and results in lower nest survival rates (McGowan and Simons 2006). Reproductive behavior (including incubation) is similar at all tidal stages (Sabine et al. 2008).

Cause of Clutch Failure

Overwash from severe flooding/storm tides and mammalian predation leading causes of clutch failure before hatch. Eggs in nests washed over by spring or storm tides have successfully hatched (RH, TV). Overwash main cause of failure in South Carolina (Thibault 2008); North Carolina, flooding main cause on river islands, mammalian predation on barrier islands (McGowan et al. 2005b); Virginia, high tides accounted for 90% of failures (Nol 1989); Maryland, overwash 57% (Traut et al. 2006); New Jersey, flooding 49% (Virzi 2010b). Mammalian predation can have profound effect on clutch survival rate; largest effect on clutch survival in New Jersey (Virzi 2008); red foxes main predator (Virzi 2010b); raccoon (Procyon lotor), striped skunk and mink also identified. In North Carolina, predation accounted for 77% of clutch failures (Davis et al. 2001); in Georgia 72% (Sabine et al. 2005, Sabine et al. 2006). Mammalian predation accounted for 62% of clutch failures at sites in North Carolina (McGowan and Simons 2006). Raccoons are a significant predator in Virginia (Wilke et al. 2007, Watts et al. 2006), North Carolina (Davis et al. 2001), and Georgia (Sabine et al. 2005, Sabine et al. 2006). Striped skunks and Norway rats (Rattus norvegicus) have been documented in nest depredations in coastal Massachusetts (E. Jedrey, unpublished). Pet dogs at the beach have been seen killing chicks and destroying eggs in nests (BW).

Avian predators also identified including gulls (Larus sp.) and fish crows (Corvus ossifragus) (Lauro and Burger 1989), Toland 1999, Wilke et al. 2007); however, effect on clutch survival found to be very small in New Jersey (Virzi 2008).

Hatching: 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. 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).

Parental Assistance And Disposal of Eggshells

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

Condition At Hatching

Chicks precocial and downy (see Appearance). 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, and middle toe are all less variable with little among-brood variance (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 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).

Chick Behavior

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 (RH). Escape diving has been observed (Hayes and Bennet 1985, RH). 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. In New Jersey, mean distance chicks moved to feed was 142 m on barrier beaches and 32 m on saltmarsh and dredge-spoil islands (TV).

Causes of Death

Most juvenile mortality takes place prior to fledging (RH). In New Jersey, mortality rate is highest during first 1–2 wks and 5th wk just prior to fledging (TV). 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. Causes of death for radio-marked chicks in North Carolina: exposure, mammalian predation, ghost crabs (Ocypode) and human disturbance (Simons and Schulte 2010). In Virginia, 43% of chick loss attributed to high tides; 29% to predation (Nol 1989). In New Jersey, mammalian predation largest effect on chick survival; gull predation very little effect (Virzi 2008). Avian predation suspected (Herring Gull, American Crow, Northern Harrier) and documented (Great Black-backed Gull) in Massachusetts (Murphy 2010). Attempt by Peregrine Falcon to take unfledged chick observed in New Jersey and Virginia (PD). Chick mortality caused by vehicular activity documented in North Carolina (Davis et al. 2001, McGowan 2004).

Parental Care: 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 (RH). 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. Proportion of time spent brooding is similar during all tidal stages and temperatures (Sabine et al. 2008). Human disturbance does not modify brooding behavior; however, foraging behavior lower in presence of vehicular activity (Sabine et al. 2008).

Parental Care: Feeding

Chicks dependent on adults for food for at least 60 d after hatching (Palmer 1967, EN). In New Jersey, chicks typically brought food by adults, but may also forage on their own as early as 2–3 wks (TV). Adults will excise shellfish from shells, then deliver soft parts to young chicks; older chicks (3+ wks) often brought unopened shellfish (TV). Adults travel up to 2 km to foraging areas (Virzi and Lockwood 2010), carrying whole food back to chicks or regurgitating it (Tomkins 1954). In New Jersey, average distance traveled by adults to forage 434 m; however, some pairs have adjacent foraging areas (Virzi and Lockwood 2010). In South Carolina, adults more typically have adjacent foraging areas possibly since birds there are resident (Thibault 2008). 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). In Florida, juveniles banded in New Jersey and North Carolina have been observed being fed by adults on wintering grounds in Dec (TV). Juvenile birds also appear to steal food from older birds (perhaps parents) on winter feeding grounds (Cadman 1980).

Cooperative (or Communal) Breeding

See Behavior: Mating System. Several cooperative associations recorded: two mated pairs tended 1 nest in Texas (Chapman 1982). In Massachusetts, communal breeding confirmed: two 6-egg clutches incubated by 3 different banded individuals (Murphy 2010). Communal nests attributed to 2 females and 1 male in New York, and believed to be a consequence of high nesting densities (Lauro et al. 1992). In New Jersey, in an area of very high nesting density, 3 adults (1 banded) tended nest containing 5 eggs in one year, and 6 eggs in a second year (TV). One nest attended by 3 adults containing 5 eggs in one year, 6 eggs in a second year, also reported in Maryland (D. Brinker, unpublished). “Trios” have been documented in Virginia often with all 3 birds incubating; in some cases, trios remained stable for several years in a row (AW).

Brood Parasitism

Not known to occur. Occasional Common Tern egg in nest (EN). In Virginia, Willet egg was observed in an oystercatcher nest (AW) and in another instance, a Herring Gull egg and an oystercatcher egg were discovered in the same scrape (RB).

Departure From Nest

Occurs within a few hours of hatching. Sustained flight (fledging) occurs at approximately 35 d (RH). In New Jersey, mean days until fledge 42 ± 6 d (Virzi 2008); Massachusetts 35–45 d (Murphy 2010). Family groups often maintained through fall staging, migration departure (RH, TV), and on wintering grounds (up to 25 wk of age; Cadman 1980).

Immature Stage

Nonbreeding flocks reported during breeding season in South Carolina (Sanders et al. 2008), New Jersey (TV) and Massachusetts (Murphy 2010). Birds of unknown age or breeding status also found in flocks in Virginia during breeding season (Wilke et al. 2005). Flock of sub-adults containing banded birds known to be 2 and 3 yr old birds consistently found at one roost site in New Jersey near breeding areas in May-Jun (TV). Natal site fidelity reported in North Carolina; 2 yr old birds banded as chicks seen near natal sites; 3 yr old birds seen paired and acting territorial (McGowan et al. 2005a). In New Jersey, 3 yr old birds seen paired and scraping at natal sites, but nests not located (TV).