Breeding

Pair Formation

First birds arrive on breeding grounds in last third of May in Manitoba (Jehl and Smith 1970), se. Northwest Territories (NWT; Obst and Spaulding 1994), and Mackenzie River Delta, NWT (Dickson et al. 1989); as early as first week of May in w. Alaska (B. McCaffery pers. comm.). Arrive singly or in small flocks of up to 10 birds (Irving 1960, Jehl and Smith 1970). Pair on territory shortly after arrival (Jehl and Smith 1970, Obst and Spaulding 1994, MAS). Males set up territory as soon as exposed ground appears through snow cover; some perform Aerial Display.

Nest-Building

No information.

First/Only Brood Per Season

See Figure 5 . Earliest nest in Manitoba: 1 Jun (3 eggs, fourth on 4 Jun); incomplete nest (3 eggs, fourth laid later) as late as 15 Jun (MAS). Peak nest initiation of eastern population occurs first week of Jun; may extend to mid-Jun due to late arrivals or renesting (Skeel 1976a, Obst and Spaulding 1994). Earliest nest of western population: 4 Jun in Yukon Territory (Irving 1960); 18 May in w. Alaska, with peak nest initiation in second half of May (B. McCaffery pers. comm.). May lay replacement clutch if first clutch is lost or deserted early on.

Earliest hatching in eastern population: last week of Jun (first chick 26 Jun; MAS); peak hatching 29 Jun through first week of Jul (Skeel 1976a, Obst and Spaulding 1994). Hatching occurs as late as 16 Jul (MAS). In Mackenzie River Delta, NWT, 6 of 9 nests hatched 6–16 Jul, 3 hatched later (Dickson et al. 1989, Gratto-Trevor 1994). Peak hatching in w. Alaska occurs in last half of Jun; latest date 6 Jul (B. McCaffery pers. comm.).

Selection Process

No data.

Site Characteristics

Depend on habitat. In Manitoba, commonly on hummock or mound (84% of nests) and near a dwarfed shrub (e.g., dwarf birch, rhododendron); also on flat heath tundra, in grass or sedge tussocks, and on gravel (Skeel 1983). In low, wet hummocky taiga and sedge tundra habitats, nests are on a hummock or hummock ridge significantly more often than random sites are; hummocks are 30–75 cm high in former habitat, 10–20 cm in latter. In hummocky taiga habitat, where shrubs are abundant, distance from nest to nearest shrub (50 cm, n = 40) is similar to that of random sites. In sedge tundra habitat, where shrubs are widely spaced, Whimbrel selects site near shrub: distance from nest to nearest shrub (32 cm, n = 19) is significantly closer than are random sites. At nest in 2 habitats, ground cover of vegetation within 1 m is significantly more dense than at random site: in hummocky taiga, 65% cover at nest versus 49% at random sites (n = 40), and in sedge tundra, 71% cover versus 56% (n = 19); no difference in heath tundra habitat where cover is uniformly high (Skeel 1983).

In Mackenzie River Delta, NWT, nests (n = 9) are on mounds or ridges of low-centered polygons, some sheltered by grasses and dwarf shrubs; tend to be in dry, low willow edges of the mounds or ridges (Dickson et al. 1989, C. Gratto-Trevor pers. comm.).

In upland shrub habitats of w. Alaska, horizontal visibility is greater at nest (n = 13) than at random sites (B. McCaffery pers. comm.). Average distance of nest to nearest shrub (15 m) and thicket (66 m) is significantly farther than random locations, and number of protected points (0–8) around nest are significantly fewer than random locations. Nest is usually on or adjacent to a hummock but, due to the abundance of hummocks, not more so than random sites.

Construction Process

Nest bowl scraped out or pressed down in the substrate.

Structure And Composition Matter

Nest is a shallow, well-defined bowl in ground, usually lined with leaves, e.g., of dwarf birch (Betula spp.), willow, Labrador tea (Ledum spp.), lapland rosebay (Rhododendron lapponicum), as well as 1 or more of grass, sedge, lichen, or small twigs (MAS).

Dimensions

In Manitoba (n = 67), inside diameter 14.1 cm (11–16 cm, 91% 13–15 cm), inside depth 3.9 cm (2–7 cm, 84% 3–5 cm) (MAS).

Microclimate

In Manitoba, nest site is often protected from prevailing winds: 73% of nests (n = 67) had an adjacent hummock edge or shrub ≥8 cm above nest along at least one of its north, northeast, or east sides. Direction of protection correlated significantly with daily maximum wind direction (north through east 69% of time); no correlation at random sites (Skeel 1983).

Maintenance Or Reuse Of Nests, Alternative Nests

Previous year’s nest cup rarely reused. In Manitoba, 2 of 97 reused in succeeding year (one by a different pair, the other unknown; MAS). In Faeroe Is., Denmark, no nests within 100 m of previous year’s site (Williamson 1946). One report of a pair with 2 nests (<30 cm apart, 2 eggs/nest, unknown if both nests incubated; Dickson et al. 1989); several of 2 birds laying in 1 nest (Harris et al. 1981).

Nonbreeding Nests

No data.

Shape

Ovate pyriform, rather pointed (Bent 1929). Because of shape, with small ends together, 4 eggs of usual clutch fit together snugly in nest cup.

Size

In Manitoba: length 58.1 ± 0.1 (SE) mm (range 51.4–65.9), breadth 40.0 ± 0.1 mm (35.5–42.8) (n = 332; MAS); and 59.6 x 39.9 mm (n = 28; Jehl and Smith 1970). In Mackenzie River Delta, NWT: length 59.2 ± 0.5 (SE) mm (55.9–63.2), breadth 41.0 ± 0.2 (38.4–42.5) (n = 17; Gratto-Trevor 1994). In Old World: 58 x 41 mm (52–65 x 36–45, n = 160; Cramp and Simmons 1983). In Manitoba, average length and width differed significantly between 2 yr; greater in year of earlier nesting (Skeel 1976a). On Shetland Is., U.K., no significant annual variation in egg volume from individual females (n = 13) or overall over 3 yr (Grant 1991b). High geographic variation in egg volume: from 40.3 to 48.0 cm³in Europe (including Iceland; Pulliainen and Saari 1993). In Manitoba, 42.5 cm³(n = 332; MAS); in Alaska, 46.4 cm³(n = 23; L. Kiff pers. comm., calculated using formula of Grant 1991b).

Mass

In Manitoba, calculated average mass of egg at onset of incubation 48.7 g (linear regression of mass against number of days after onset of incubation on 299 eggs); average mass significantly different between 2 yr (Skeel 1976a). Weight loss of egg during incubation 19.3% of initial weight. Egg about 12% of average female mass (Skeel 1976a, Grant 1991b); 4-egg clutch about 50% of female’s mass.

Color

Ground color varies from bluish pea green through light and dark shades of olive buff to light olive green, occasionally Isabella color or ecru olive. Markings are blotches, spots, and dots of various browns, including bone, warm sepia, Saccardo’s umber, olive, and buffy. Markings numerous, sometimes more concentrated at large end of egg (Bent 1929).

Surface Texture

Smooth with little or no gloss (Bent 1929).

Eggshell Thickness

For eggs collected in Manitoba from 1933 to 1945, mean egg thickness index 1.05 ± 0.006 (SE) mm (80 eggs of 20 clutches); from 1951 to 1953, 1.09 ± 0.011 mm (27 eggs of 7 clutches). Significant difference is likely due to sampling artifact (Morrison and Kiff 1979).

Clutch Size

Usually 4 eggs. See Demography and Populations: measures of breeding activity, below.

Egg-Laying

From 1 to 3 d between laying of successive eggs (Skeel 1976a); clutch normally laid in 4–6 d (MAS). Intraspecific egg dumping rare: 0 of 134 nests in Manitoba (MAS), and 1 of 120 nests on Shetland Is., U.K., had >4 eggs (Grant 1991b).

Onset Of Broodiness And Incubation In Relation To Laying

Some incubation before clutch is complete; continuous incubation may start as late as 1 d after fourth egg is laid (Skeel 1976a).

Incubation Patches

Two large oblong patches, 1 on each side of midline, on both sexes.

Incubation Period

From 22 to 28 d. In Manitoba, 24–28 d (n = 80; W. Lin pers. comm.); also 22 (Jehl and Hussell 1966) and 23.5 d recorded (Skeel 1976a). In Old World, 23–28 d; on Shetland Is., U.K., mean = 26.0 d (n = 23; Pulliainen and Saari 1993).

Parental Behavior

Both sexes incubate. In Manitoba, female incubates about 65% of 24-h day (Skeel 1976a). Incubation bouts vary from 1–10 h during late incubation to >14 h during hatching. Change of incubating bird may be preceded by exchange of Low Trill Call, initiated by on- or off-duty bird (Skeel 1976a; see Sounds: vocalizations, above). Relieving bird flies to nest site when mate is on nest or after mate has flown away; usually no vocalizing (W. Lin pers. comm.). In w. Alaska, nonincubating adult is frequently near nest (82% of the time, n = 73; B. McCafferey pers. comm.); may enhance nest success through increased vigilance and mobbing of predators. Nest is attended almost continuously, although occasionally there is no adult (Pulliainen and Saari 1993, MAS).

Hardiness Of Eggs

Little information. Chilled eggs are common prior to completion of clutch; cold eggs, with incubation subsequently resumed, are occasionally found up to just prior to hatching (MAS).

Preliminary Events And Vocalizations

Little information. Chicks are sometimes audible before egg is star-pipped (Williamson 1946).

Shell-Breaking And Emergence

Hatching occurs at any time of day; duration of hatching from first star-pip to damp chick is 1–3 d, occasionally 4 d (MAS). Once egg has hole-pipped, chick hatches in <7–24 h (MAS). Hatching is asynchronous, but all eggs in most clutches hatch within 1–2 d (87%, n = 47 clutches); may span 4 d (Skeel 1976a). Parents rarely abandon pipped egg after others hatch (observed once); abandon starred egg slightly more often (3 times; W. Lin pers. comm.). Continue incubating unpipped egg for about 1 d after others hatch (5 nests, unpipped egg infertile; MAS).

Parental Assistance And Disposal Of Eggshells

Parents normally do not assist hatching of chicks. One incident of apparent assist where 48 h passed after egg hole-pipped, during which 3 other eggs hatched: adult carefully inserted bill into 1.3-cm crack for about 2 min, opening mandibles as it did so, then incubated egg and chicks until hatching complete 30 min later (Tremaine 1974).

Once young are dry, parent removes eggshell of early hatching by walking or flying, carrying eggshell in bill; eggshell sometimes at nest after hatching complete (Williamson 1946, MAS).

Condition At Hatching

Covered in down; mobile soon after hatching. May leave nest within 1–2 h to feed nearby; first chicks hatched often do so before last egg hatches (Grant 1991a, MAS). Legs and bill blackish, bill straight and bluntly tipped, eyes open. In Manitoba, mass of day-of-hatch chicks 34.2 ± 0.28 (SE) g (range 27.0–45.5), bill length 16.5 ± 0.08 mm (14.5–19.1), tarsus 36.5 ± 0.13 mm (33.5–39.5); weight 9.0% of adult, bill length 18.8%, tarsus length 62.7% (n = 102; Skeel 1976a). In Finland, mass at 1 d: 31.0 ± 3.06 (SE) g (range 24.5–35.0), 8.6% of adult weight (n = 29; Pulliainen and Saari 1993); heavier on Shetland Is., U.K., at 39.9 ± 0.42 (SE) g (n = 96 brood means; Grant 1991b). Average weight at 1 d differed significantly between 2 yr in Manitoba (Skeel 1976a), but not between 3 yr on Shetland Is. (Grant 1991b). Hatchling weight correlates significantly with egg volume (r = 0.86); both correlate with individual females between 3 successive years (r >0.73; Grant 1991b).

Growth And Development

Little information. Newly hatched chicks lie quietly when warned by parents; older chicks are more likely to run initially, then freeze. Chicks exhibit Threat Display, piping aggressively with wing-stumps outstretched, some at <1 d old; at 16 d, only scapulars and wing-coverts feathered; at 30 d, Juvenal body plumage complete, but not wings and tail (Williamson 1946). Bill length averaged 18.4 mm (range 16.4–24.6), or 21% of adult length, in first week of life at Churchill, MB (n = 8; EPM).

Brooding

May brood chicks several hours on nest site after all hatch, rarely up to 1.5 d; will brood young chicks in empty nest cup other than where hatched (MAS). Unclear to what age young are brooded or how much time is spent brooding; appears that brooding is terminated by day 3, except perhaps during severe weather (W. Lin pers. comm.).

Feeding

Young not fed by parents. At Churchill, MB, feed on insects and ripening berries; in mid-Jul on small, newly emerged Diptera (chironomids, etc.; EPM).

Nest Sanitation

Not a concern; chicks usually leave nest within 1 d of last chick hatching (MAS).

Parental Carrying Of Young

Never observed.

Never observed.

Not reported. But see Nest: maintenance or reuse of nests, alternate nests, above.

Departure From The Nest

Usually leave within hours of last chick hatching; delayed if weather is poor. In Manitoba, splitting of brood not observed (n = 12; W. Lin pers. comm.). On Faeroe Is., chicks usually depart with both adults; 1–2 chicks may depart with 1 adult while other adult broods pipped eggs (Williamson 1946).

Growth

Little information. Time to fledging 28–30 d on Shetland Is. (Grant 1991a); 5–6 wk on Faeroe Is.; at 30 d, fully feathered except for wings and tail, incapable of flight (Williamson 1946). Bill of 12-d-old chick 22.8 mm, tarsus 40.5 mm (n = 2; Skeel 1976a). Bill of one 28-d chick 30 mm, wing 135 mm; wing of nearly-fledged chick 170 mm; at 5 wk, young can replicate Low Trill Call (see Sounds: vocalizations, above; Williamson 1946). In Aug study skins of juveniles from Alaska to Panama, tarsus 58.2 mm (range 54.1–64.2, n = 18) and culmen 61.5 mm (50.6–71.7, n = 21), 100 and 70% of adult, respectively; in Oct from wintering grounds, culmen 80.4 mm (range 69.5–84.4, n = 5), 92% of adult (EPM).

Association With Parents Or Other Young

Chicks initially receive biparental care (Skeel 1978) but as early as 3 d to 2 wk are accompanied only by male; male remains with brood until near fledging (n = 6; W. Lin pers. comm.). On Shetland Is., U.K., both parents usually remain until near fledging, and male for sometime after (Grant 1991a); on Faeroe Is., brood of older chicks may periodically be split by parents (Williamson 1946). No evidence of intersibling conflict.

Ability Of Get Around, Feed, And Care For Self

No data.

Juveniles migrate south about 1 mo later than most adults (see Migration: migratory behavior, above). Most overwinter in Central and South America, where they undergo Prebasic molt of body feathers and some flight feathers (see Appearance: molts and plumages, below). Yearlings spend northern summer on wintering grounds (Cramp and Simmons 1983); possibly also 2-yr-olds (Skeel 1983).