Breeding

Pair Formation

In Georgia, pairs form before territories are established, by mid-Mar (Tomkins 1944). Territories and nests established by first week of Apr in Texas (Bergstrom 1988a); territories established by mid-Apr in Georgia (Corbat 1990). In a resident population in Venezuela, pair formation and breeding ac-tivities began in Mar–Apr (Morrier and McNeil 1991).

Nest-Building

Nest is a scrape in sand that requires little construction. Bergstrom (1982) observed a female laying an egg in a scrape that had been made the same day.

First/Only Brood Per Season

In 2 yr in Texas, 15 Apr was earliest nest date, but presence of chicks indicated that earlier nests (1 Apr) must have been present (Bergstrom 1988a; Fig. 6). Latest nest start in Texas 19 Jun; egg-laying peaked 25–29 Apr and 26–31 May in 1979 and 21–23 Apr and 18–30 May in 1980 (Bergstrom 1982). Second peak each year may be due to renesting after failure of first nest. In Georgia, egg-laying begins about mid-Apr and continues through end of Jun; a few nests are active through third week of Jul. In 1987, nests were present in various stages of incubation from third week in Apr through second week in Jul, with slight peaks in laying 21–30 Apr and 10–30 May. Much renesting after previous nest failure (CAC).

Estimated time required to complete clutch of 3 eggs for each of 6 Texas nests was 104–125 h, 144–149 h, 119 h, 120 h, 142 h, and 145 h, respectively (Bergstrom 1988a).

Second/Later Brood(S) Per Season

Mean time from nest failure to start of new clutch for 7 renesting attempts was 7.6 d ± 1.6 SE (range 5–13; Bergstrom 1988a). Second broods are thought not to occur except when first is lost. Corbat (1990), however, recorded 1 instance of a female apparently hatching 2 broods successfully in 1 season; second nest was about 6 km from first and was begun 7–8 d after female was last seen in her previous territory. It was not known if same male was involved each time or whether chicks from first brood survived.

Selection Process

Males make multiple scrapes within their territories. Male bows toward scrape when approached by female, who may then either move away if uninterested or enter the scrape (Bergstrom 1988b).

Microhabitat

Nests in Georgia frequently are close to drift trash or similar low windbreaks; usually not near thick vegetation (Tomkins 1944).

In Texas, nests found on bare soil or pavement, usually near clump of vegetation (Bergstrom 1988a); 57 of 58 nests had plant stems within 0.5 m. Few nests were near objects, but few objects were present. At 1 site, nests were mostly in center strip or at edge of road surfaced with rock, shells, or gravel. At another site, nests were on former airfield areas of concrete or asphalt. Distribution of vegetation in 8 sectors around nests was nonrandom, with more nests having vegetation on south and southwest sides. Prevailing winds at the site were from the southwest. Mean distance from nest to nearest object was 12 cm ± 3.6 SE (range 2–30).

Corbat (1990) quantified habitat variables for 116 Wilson’s Plover nest sites on Georgia barrier islands (see Appendix). Nest sites were highly variable, especially with regard to amount of vegetation and distance from ocean. All but 1 nest was on sand sub-strate containing varying amounts of shell; 1 nest was on a pile of wrack. No differences in percentage of vegetation cover among 4 quadrants around the nests; 94 of 116 nests had vegetation within 0.5 m. Only 26 nests were within 1 m of an object larger than 2.5 × 2.5 cm.

When microhabitat variables were compared between successful and unsuccessful nests, percentage of vegetation cover was higher at successful nests than at unsuccessful nests (Corbat 1990).

Site Characteristics

Tomkins (1944) described nesting habitat as open areas of sandy islands and edges of dunes in areas with high salinity. At 2 Texas sites, nests were located along roads or on abandoned airfields amid sparsely vegetated salt flats (Bergstrom 1988a). In Georgia, Wilson’s Plovers nest on dry sand beach, on beach side of primary dunes, on sandy areas behind primary dunes, in newly accreted beach areas, and on sandy overwash areas bordering salt flats (Corbat 1990). On Metompkin I., VA, 11 of 12 nests found over 3 yr were on high shelly beach near base of dune; 1 was on strip of sparsely vegetated sand between dune and mudflat. Ten of the nests were within 25 m of a Least Tern colony, and 6 were closer to a Piping Plover nest than to a Wilson’s Plover nest (Bergstrom and Terwilliger 1987).

Construction Process

Male makes scrape in substrate; female sometimes modifies scrape started by male. At some nests, birds arrange bits of shell or other objects around or in nest cup (Bergstrom 1982, 1988b, Corbat 1990).

Structure And Composition Matter

In Texas, nests were located on soil; on roads of crushed shell, rock, or gravel; and on abandoned concrete or asphalt air-fields where surface was cracked by vegetation (Bergstrom 1982, 1988a). Nests occurred on beaches there, but no beach surveys were done (PWB). Of 116 beach nests in Georgia, 115 were on sand and 1 was on wrack (Corbat 1990). A rim of material (wrack, shell, leaves, florets, etc.) was present on 9.5% of the Georgia nests, and 22.4% of the nests were lined with shell, wrack, or other materials.

Dimensions

Nest scrape about 8 cm in diameter (Bergstrom 1988b).

Microclimate

In Texas, Bergstrom (1989) recorded temperatures at nest bottom and shaded air temperatures nearby 5 cm off the ground. Mean daytime temperatures at nest bottom were 33.5°C ± 4.0 SD (n = 865) in 1980 and 33.8°C ± 1.4 SD (n = 158) in 1981. Mean daytime ambient temperatures were 30.3°C ± 4.9 SD (n = 856) in 1980 and 32.9°C ± 2.4 SD (n = 109) in 1981.

Maintenance Or Reuse Of Nests, Alternate Nests

Reuse of nests and alternate nests not observed. Nest maintenance consists only of maintaining the scrape against drifting sand. Maintenance done mainly by adult sitting on nest continuously during drifting condition, or by adult rotating in nest with breast down. (CAC).

Nonbreeding Nests

Not known.

Shape

Oval to short oval (Baicich and Harrison 1997).

Size

Of 78 eggs laid by 20 different females in Texas, average length 35.23 mm ± 0.14 SE, breadth 25.85 mm ± 0.06 SE (Bergstrom 1988a). Egg dimensions varied significantly among females. Eggs of a given female were not consistently smaller (on basis of volume) in second nests than in first nests.

In Georgia (n = 304 eggs, 116 clutches), average length 35.43 mm ± 0.07 SE, breadth 26.03 mm ± 0.06 SE (Corbat 1990).

In Western Foundation of Vertebrate Zoology (WFVZ) collection, 67 eggs (22 clutches) of C. w. wil-sonia averaged 35.36 mm (range 33.23–36.81) in length and 25.88 mm (range 24.84–26.67) in breadth. From same collection, 37 eggs (15 clutches) of C. w. beldingi averaged 36.46 mm (range 34.96–37.96) in length and 26.37 mm (range 25.53–27.24) in breadth.

Mass

Eggs lose mass during incubation. Three eggs at 1 nest in Georgia were weighed between 20 Apr (when first egg was laid) and 19 May (Tomkins 1965). Newly laid eggs weighed 12.6–13 g, those near hatching 10.5–11 g. Mean weight of 14 eggs in Texas was 12.0 g; 11 were weighed during first half of in-cubation (Bergstrom 1982).

Color

Cream-colored to buff. Spotted and speckled heavily, along with blotches and scrawls. Markings may be black, dark brown, or gray (Baicich and Harrison 1997, CAC).

Surface Texture

Shell smooth, and without gloss or slightly glossy (Baicich and Harrison 1997).

Eggshell Thickness

No data on thickness. Empty shell weight for 67 eggs (22 clutches) of C. w. wilsonia averaged 0.769 g (range 0.698–0.837). Mean weight for 37 eggs (15 clutches) of C. w. beldingi was 0.786 g (range 0.683–0.889; WFVZ).

Clutch Size

Of 51 nests in Texas, 1 had 4 eggs, 45 had 3, and 5 had 2 (mean 2.92 ± 0.047 SE; Bergstrom 1988a). In Georgia, for 51 nests known to be complete, 46 had 3 eggs and 5 had 2 (mean 2.90 ± 0.09 SE; Corbat 1990).

Egg-Laying

One observation (Bergstrom 1982): Male and female had been making scrape for at least 5 d; after scrape exchanges on fifth day, female crouched over scrape and laid first egg.

Estimated time required to complete clutch after first egg is laid is 4–6 d (Bergstrom 1988a; see Phenology, above).

Onset Of Broodiness And Incubation In Relation To Laying

Regular incubation does not begin until third egg is laid, although parental attentiveness increases during clutch completion (Bergstrom 1988a). Male share of attentiveness is greater than female share during clutch completion; afterward female is more attentive (Bergstrom 1986).

Incubation Patch

No information.

Incubation Period

About 25 d. Tomkins (1965) es-timated 25 d for 1 nest. Bergstrom (1988a) estimated 23–27 d at 5 nests. For 1 nest where exact time was known, incubation time was 25 d 3 h from laying of third egg to hatching of third egg. Corbat (1990) reported 2 nests with minimum incubation period of 25 d, 1 nest incubated a minimum of 29 d, and 1 in-cubated a minimum of 39 d (on fortieth day, nest scrape was empty, with no signs of disturbance).

Parental Behavior

Parents vary their attentiveness to clutch depending on ambient temperature (Bergstrom 1989). Adults use shading, sitting on eggs, and belly-soaking (parent sits or crouches over eggs with matted, muddy breast-feathers) to regulate nest temperature. Attentiveness increases during periods when shaded air temperature 5 cm off the ground is <24°C and as temperatures increase from 30.5 to 41°C, suggesting that incubation is used to both warm and cool eggs. As temperatures increase, birds change from shading to sitting and finally belly-soaking. Belly-soaking is rare, but it is used at hottest times.

In Texas, total daytime nest attentiveness averaged 76% (range 0–100, depending on time period; Bergstrom 1981). Male share of attentiveness is greater during egg-laying (63%) and hatching (41%) than during incubation (30%; n = 60 nest days; 48 during incubation, 5 during egg-laying, 7 during hatching; Bergstrom 1986). Females carry out more daylight incubation, but males appear to incubate most of the night. Because total attentiveness at night is higher (92%), incubation duties are shared about equally. There are significant differences in sex roles among pairs. Absence of one parent causes the other to increase time at nest, but total nest attentiveness is less, seemingly with no effect on hatching success (Bergstrom 1986).

At 3 Texas nests, time on nest spent shading eggs over an air temperature range of 31–41°C ranged from 8 to 100% of time on nest (n = 126; Bergstrom 1982). Percentage of time shading increased with air temperature, up to about 37°C. Above that air temperature it declined, as predicted by Drent (1973). The assumption is that above 37°C, the parent could cool eggs more effectively by sitting on them than by shading them, with or without belly-soa-king. Belly-soaking was later observed at 1 of the 3 nests analyzed, which was located on pavement, but it was not known if it was used during the period analyzed.

Hardiness Of Eggs Against Temperature Stress; Effect Of Egg Neglect

For Texas nests, temperatures were measured at nest cup, inside egg, and in shaded air (Bergstrom 1989). Maximum nest temperature reached was 48.5°C at a nest on pavement. Bergstrom estimated that the start of overheating (egg temperature 42°C) would be reached when nest temperature was 43.2°C. That nest temperature was exceeded between 12:00 and 16:00. At those times, parents used belly-soaking to cool eggs. It was not possible to relate nest and egg temperature to hatching failure.

Preliminary Events And Vocalizations

Chicks hatch about 30 d after clutch initiation (Bergstrom 1982, CAC). In 1 instance, pipping started 2 h before hatching. Chicks can be heard pecking and peeping inside egg before and during pipping (CAC).

Shell-Breaking And Emergence

Large end of shell is removed first (Bergstrom 1982). At some nests, hatching takes <24 h; at others, it takes longer, but <48 h. Hatching interval between eggs is usually unequal within a clutch, with one 24-h and one 5- to 10-h interval, but which interval (egg A–B or B–C) is longer and which is shorter vary (Bergstrom 1988a). In 1 instance, when a third egg failed to hatch, parents incubated it another day before abandoning it (Bergstrom 1982).

Parental Assistance And Disposal Of Eggshells

Parental assistance in hatching not known to occur. Parents do, however, promptly remove eggshells after hatching; they fly to drop them far from nest (Bergstrom 1982).

Condition At Hatching

In Texas, newly hatched chicks are wet and have egg tooth (Bergstrom 1982, 1988a). Mean body mass at hatching for 18 chicks was 9.3 g ± 0.54 SE. Mean culmen length 6.0 mm ± 0.13 SE. Chicks walk within 1–2 h after hatching; begin to hide in vegetation within a few hours. One family moved away from nest 2 h 11 min after last chick hatched.

Growth And Development

No information.

Brooding

Apparently little brooding occurs during day in warm climates in Texas and Georgia (Bergstrom 1982, CAC). Parents may shade chicks during heat of day (PWB), or chicks remain hidden in vegetation. Either the parent or a chick may initiate brooding (Bergstrom 1982). Parents appear to defend an area around chicks if other Wilson’s Plovers are nearby (Bergstrom 1988a).

Feeding

Precocial young feed themselves. Chicks observed feeding among plants in low, wet salt flat (Bergstrom 1982) and along large pool at top of intertidal zone (CAC). Feeding areas not usually near nesting areas (Bergstrom 1982, CAC). Diet not known.

Carrying Of Young

Not known to occur.

Not known to occur.

Not known to occur.

Departure From Nest

Young can walk within 1–2 h after hatching, and brood may depart nest within 2 h after hatching is complete (Bergstrom 1988a, CAC). Time to fledging unknown. Tomkins (1944) reported a minimum of 21 d. Age at first flight unknown.

Growth

No information.

Association With Parents Or Other Young

Young remain with parents after hatching. Parents appear to defend area around chicks when other Wilson’s Plovers are present. Other adults may adopt young (Bergstrom 1988a).

No information.