Breeding

Pair Formation

Generally occurs on or near breeding grounds; in years of late snow melt, birds may already be paired on arrival (Holmes 1966b), although this needs to be confirmed. At Churchill, Manitoba, old mates arrive separately and re-pair immediately on old territory (J. Jehl pers. comm.). Males typically arrive first. On Yukon-Kuskokwim Delta, AK, males arrive 7–8 May (range 1–15 May; C. Ely pers. comm.). Males arrive n. Alaska end of May (Johnson and Herter 1989); all pairs settled by mid-Jun (Holmes 1966b). In Finland, no apparent difference between arrival of previously color-banded male and female C. a. schinzii (Soikkeli 1967 contra Heldt 1966).

Nest-Building

Nest-building activity of pair may last 3–4 d (Holmes 1966b); probably a function of experience (J. Jehl pers. comm.).

First/Only Brood Per Season

Figure 5 . On Yukon-Kuskokwim Delta, AK (C. a. pacifica), earliest completed 4-egg clutches 24 May (1967, 1968) and 1 Jun (1966); peak laying period between 26 and 28 May (1967, 1968) and around 7 Jun (1966) (Holmes 1971). At Barrow, AK (C. a. arcticola), early completed nests 6 Jun (1963) and 9 Jun (1962); peak laying period 12–18 Jun; latest laying date 6 Jul (1963) (Holmes 1966b). Median nest initiation (first egg) dates at Prudhoe Bay, AK (C. a. arcticola), 6–18 Jun in 10-yr period; the greater the snow cover, the later nests are initiated (TERA 1993). Around Churchill, Manitoba, laying period of C. a. hudsonia 8 Jun–15 Jul; day-old chicks as late as 21 Jul (Jehl and Smith 1970). At La Perouse Bay, Manitoba, hatch dates for 7 nests ranged from 3 to 17 Jul (median 7 Jul). In Rasmussen Lowlands, Northwest Territories, 2 nests found hatched on 2 Jul (C. Gratto-Trevor pers. comm.). First-year C. a. arcticola lay significantly later than returning adults (Norton 1972).

Second Brood Per Season

In North America, significant numbers appear to renest if eggs are lost early, but only 1 brood raised/season (Holmes 1966b, Holmes 1971). In Europe, egg-laying for second clutch may begin as early as 4 d after loss of initial clutch (Soikkeli 1967); Heldt (1966) reports relaying to range from 3 to 14 d after loss of clutch.

Selection Process

Males generally select territories, but females may select a territory and mate with male that is there; selection varies with snow cover, food, and moisture content of tundra (Holmes 1966b, R. T. Holmes pers. comm.). Females select scrape made by male (J. Jehl pers. comm.). In n. Alaska, 6 returning Dunlin nested an average of 292 m from their nest site of the previous year (Troy and Carpenter 1990). In Europe, breeding Dunlin more likely to nest near the highly vigilant Golden Plover (Pluvialis apricaria) (Byrkjedal and Kalas 1983); not known to do so in North America.

Microhabitat

See also Habitat: breeding range. In n. Alaska, often nests on strangs or around moist, low-centered polygons (D. Troy pers. comm.); nests in or next to clumps of grass.

Site Characteristics

See Habitat: breeding range.

Construction Process

Male first uses feet to form depression; shapes cup with breast, tail, and wingtips extended vertically into air; then stands next to cup and tosses grasses, sedges, and willow (Salix) leaves into cup (Holmes 1966b, REG). In Churchill, Manitoba, male not observed to toss material into the nest cup (J. Jehl pers. comm.).

Structure And Composition Matter

Typically contains grasses and willow leaves.

Dimensions

Inside diameter 90–102 mm; inside depth 51–76 mm, total depth 76–122 mm (Bent 1927).

Microclimate

Nest temperature of incubating C. a. arcticola 15–20°C at beginning stages of incubation, 20–30°C just before eggs hatch (Norton 1972).

Maintenance Or Reuse Of Nests, Alternative Nests

In Alaska, occasionally reuses old nest cups (Holmes 1966b); at Churchill, Manitoba, nest cups often reused (J. Jehl pers. comm.). One nest cup used by a phalarope (Phalaropus sp.), a Semipalmated Sandpiper, and a Dunlin in subsequent years (Gratto et al. 1985).

Nonbreeding Nests

Male may make several scrapes in breeding territory before actual breeding cup is selected by female.

Shape

Oval to pyriform (Cramp and Simmons 1983).

Size And Mass

From collection of 20 clutches (79 eggs) gathered throughout North America prior to 1947, mean length (mm) 36.07, range 33.90–38.62; breadth (mm) 25.35, range 24.56–26.39; empty shell mass (g) 0.523, range 0.462–0.621 (means and ranges based on clutch averages, Western Foundation of Vertebrate Zoology [WFVZ]). For 17 eggs from C. a. hudsonia at La Pérouse Bay, Manitoba, length (mm) 35.99 ± 0.82 (± SD), breadth (mm) 25.19 ± 0.39, weight (g) 11.12 ± 1.18 (C. Gratto-Trevor pers. comm.). For 20 eggs from C. a. schinzii, length (mm) 34.23 ± 1.17, breadth (mm) 24.28 ± 0.57, volume (cc) 9.36 ± 0.54; no significant difference in size of eggs in first versus second clutch; body size positively correlated with egg size (Väisänen et al. 1972). In Europe, egg size lowest at high arctic latitudes (Väisänen 1977). Two 4-egg clutches of C. a. arcticola accounted for 69 and 79% of the female’s body mass (D. Parmelee pers. comm.).

Color

Background color generally olive to olive-brown, but may range from buff to blue-green; small splotches and swirls ranging from light brown to orange-brown to black over much of egg, especially heavy at the wide end of the egg (Cramp and Simmons 1983).

Surface Texture

Smooth and slightly glossy (Cramp and Simmons 1983).

Eggshell Thickness

From collection of 20 clutches (79 eggs) from throughout North America prior to 1947, mean thickness (mm) of shell 0.129, range 0.118–0.142 (WFVZ). More recent data on eggshell thickness lacking.

Clutch Size

Typically 4 eggs. Replacement clutches occasionally 3 eggs (Norton 1972).

Egg-Laying

In s. Finland, females observed to lay consecutive eggs in intervals of 30–36 h; clutch completed in approximately 4.5 d (Soikkeli 1967). In n. Alaska and Churchill, Manitoba, interval between eggs 24 h (MacLean 1974, J. Jehl pers. comm.). Laying interval may be limited by availability of calcium (MacLean 1974, Underhill 1994).

Onset Of Broodiness And Incubation In Relation To Laying

See Parental Behavior.

Incubation Patches

Both sexes possess well-developed patches.

Incubation Period

In n. Alaska, 21–22 d (Holmes 1966b); Churchill, Manitoba, 20–21 d (maximum 23 d) (J. Jehl pers. comm.).

Parental Behavior

Sporadic attendance of nest until fourth egg laid; within hours of the last egg being laid, almost continuous attendance (97.6 ± 0.3 SD % time within 24-h period); nest attendance significantly higher during colder parts of the day (afternoon and night) and on cold days (Norton 1972). In early stage of incubation, females apparently incubate more than males; this reverses as hatching approaches (Holmes 1966b). Females incubate more at night (Cramp and Simmons 1983).

Hardiness Of Eggs

Nest attendance in the Arctic generally high >97% time/24-h period), apparently to prevent embryonic chilling (Norton 1972), although 1 nest successfully hatched where 1 mate was removed after 7 d and nest attendance was only 59% over the last 15 d of incubation (Erckmann 1981). Unincubated 2-egg clutch covered with snow for 16 h, clutch subsequently completed by adults and all 4 eggs hatched (Norton 1972).

Preliminary Events And Vocalizations

See Sounds: vocalizations.

Shell-Breaking And Emergence

Generally synchronous. Hatching of all 4 eggs typically within 12–24 h, occasionally 48 h (Holmes 1966b).

Parental Assistance And Disposal Of Eggshells

Shells removed immediately by adults or crushed into nest (Cramp and Simmons 1983).

Condition At Hatching

Precocial. Young begin to wander from nest shortly after they are dry. See also Appearance: molts and plumages, below.

Growth And Development

Weigh approximately 7 g at hatching and reach adult weight of 50–60 g within 3–4 wk (Holmes 1966b). See also Fledgling Stage, below.

Brooding

Generally, both parents participate, although typically the male assumes more of this role as the chicks grow; sometimes only the male incubates (J. Jehl pers. comm.).

Feeding

Adults lead young to areas with abundant insect populations, but young find their own food; are not fed directly by adults.

Nest Sanitation

See Hatching, above.

Not known to occur in this species.

Not known to occur in this species.

Departure From The Nest

Young depart from nest within a few hours of all eggs hatching. If some eggs are delayed, 1 parent may take first young away, leaving 1 adult (male?) with eggs. If chicks hatch in evening, usually stay at nest until morning; will stay on nest longer if cold and rainy/snowy (J. Jehl pers. comm.).

Association With Parents Or Other Young

Young generally stay with parent(s) until shortly before or when they can fly (Holmes 1966b). Female typically first to leave brood (Holmes 1966b); male stays with brood on average 19 d (range 9–25 d), female 6 d (1–11 d) (Cramp and Simmons 1983).

Ability To Get Around, Feed, And Care For Self

Chicks precocial. In Alaska, time between hatching and first flight 21–26 d (Holmes 1966b); at Churchill, Manitoba, 18–20 d (J. Jehl pers. comm.).

After fledging, juveniles group into small flocks inland from coast while adults flock along coast (Holmes 1966b). Most immatures move to coast to mix with adults in Aug; juveniles seldom found inland after early Sep (REG).