Demography and Populations

Age At First Breeding; Intervals Between Breeding

Many Dunlin do not begin breeding until second breeding season. C. a. arcticola: based on plumage characteristics, R. Holmes (pers. comm.) estimated that 29% of returning first-year birds at Barrow, AK, bred. C. a. hudsonia: at least some returning first-year birds breed (J. Jehl pers. comm.). In Scotland, first-year birds rarely breed (Jackson 1994). In s. Finland, one-third of all birds first breed at age 1 yr; in n. Finland, almost all breed at age 2 yr (Soikkeli 1967).

Clutch

See Breeding: eggs, above.

Annual And Lifetime Reproductive Success

In n. Alaska, of 18 C. a. arcticola nests, 78% hatched and 22% depredated (Erckmann 1981). At La Pérouse Bay, Manitoba, of 25 C. a. hudsonia nests found, 20% hatched, 52% depredated, 20% fate unknown, and 8% destroyed (C. Gratto-Trevor pers. comm.). In Europe, of 203 C. a. schinzii nests, 29.6% hatched, 60.0% depredated, 7.9% trampled, and 2.5% deserted; fledging success estimated at 36.3% (Jönsson 1991).

Number Of Broods Normally Reared Per Season

See Breeding: phenology, above.

Annual survival probabilities for adult C. a. pacifica returning to wintering grounds range from 0.69 to 0.77; first-year birds 0.31–0.35 (Warnock 1994). These rates are slightly lower than minimum annual survival rates of breeding European Dunlin; in Finland, Soikkeli (1970) had return rates of 0.77 for adult males and 0.72 for adult females; in Sweden, Jönsson (1991) had return rates of 0.89 for adult males and 0.77 for adult females. For C. a. schinzii, mean life expectancy of males 8.6 yr, of females 3.9 yr, of adults 5.4 yr; oldest birds in this study 16 and 17 yr (Jönsson 1991). One European Dunlin recaptured at minimum age of 24 yr (Lindholm and Hjort 1975 in Stiefel and Scheufler 1989). C. a. pacifica minimum age of 14 yr have been recaptured and released at Bolinas Lagoon, CA (NDW).

Nematodes of genus Skrjabinoclava fairly common (1–68%) in proventriculus of different subspecies of Dunlin (Wong and Anderson 1990, Anderson et al. 1994). Sixteen parasite taxa, including 6 digeneans, 8 cestodes, 2 acanthocephalans, and 1 nematode found in intestine and mesenteric veins of wintering C. a. pacifica collected in n.-central California (Ching 1990). At Kvichak Bay, AK, 4 species of cestodes found in 5 of 8 birds sampled (Schmidt and Neiland 1968). Acanthocephala found in 25 of 26 Dunlin collected at Juneau, AK (Van Cleave and Rausch 1950). Chewing lice families Philopteridae and Menoponidae found on head feathers of 11 of 13 C. a. pacifica examined (Hunter and Colwell 1994). In Europe, pox virus observed once (Green 1969).

Most mortality (76%) thought to occur on wintering grounds and migration (Evans 1991). Raptor predation probably accounts for most mortality of wintering Dunlin, up to 21% of the population wintering at Bolinas Lagoon, CA (Page and Whitacre 1975); 2–21% wintering in Scotland (Whitfield et al. 1988, Cresswell and Whitfeld 1994); 10–23% of the midwinter population in Teesmouth, England, taken by Merlin (Townshend 1984). In Europe, cold weather known to kill Dunlin (Clark 1982), but no such data for North America. Breeding: quantitative data lacking for North America.

Natal Philopatry

At Barrow, AK, 6% (n = 34) of birds banded as young bred within 0.4 km of their birth place (Holmes 1966b). In Germany, 3% (n = 448) of birds banded as young returned to study area (Heldt 1966). In Finland, 26% of males and 33% of females bred within 1 km of natal site, rest within 2–5 km (Soikkeli 1970).

Fidelity To Breeding Site And Winter Home Range

Females more likely to disperse than males. In Scotland, 90% of returning adult males and 65% of females bred within 100 m of previous year’s nest (Jackson 1994). In Finland, 76% of the birds returning to mate with previous year’s mate bred within 100 m of previous year’s site; 80% of males with new mates returned to within 100 m of previous year, whereas only 20% of females with new mates did so (Soikkeli 1970). On winter grounds in California, adults shown to have high fidelity to Bolinas Lagoon; resighting probabilities as high as 97% in some years (Warnock 1994). Some individuals always stay for entire winter season (Oct–Mar) whereas others leave midwinter, particularly in wet years (Warnock et al. 1995).

Dispersal From Breeding Site Or Colony

In Scotland, mean postnatal dispersal distance of males less than that of females (0.55 vs. 2.1 km); maximum dispersal distances for returning adult males versus females: 0.45 km versus 4.0 km. Among unsuccessful female breeders, >50% more likely to nest >100 m away in the following year (Jackson 1994).

Home Range

See Behavior: spacing, above.

Numbers

C. a. pacifica estimated at 450,000–600,000 individuals (Page and Gill 1994). Accurate estimates for C. a. arcticola and C. a. hudsonia lacking. For breeding C. a. arcticola, also see Habitat. From 1981 to 1992 at Prudhoe Bay, AK, yearly nest densities ranged from 3 to 10 nests/km2, mean = 7.5; breeding-season densities of birds ranged from 14.5 to 25.3 birds/km2; postbreeding densities ranged from 6.0 to 57.0 birds/km2, mean = 19.1 birds/km2, n = 6 yr; highest breeding densities seem to be between 3 and 7 km from coast (TERA 1993). Dunlin breeding at Kolomak River, AK, averaged 30 pairs/40 ha and at Barrow, AK, 6 pairs/40 ha (Holmes 1970). In s. Finland, Soikkeli (1967) reported 16–17 pairs/40 ha.

Trends

Based on Christmas Bird Counts, Paulson (1993) suggests that winter populations of C. a. pacifica in the Northwest have declined. At Prudhoe Bay, AK, between 1981 and 1992, a significant downward trend in breeding-season densities of C. a. arcticola (TERA 1993). Trends of fall migrating C. a. hudsonia from 1974 to 1991 varied but not significantly: 1974–1979: -7.89% annual change; 1980–1985: -3.61%; 1986–1991: -7.07% (Morrison et al. 1994). Further monitoring of populations should be a priority.

Based on results of a long-term study at Prudhoe Bay, AK, TERA (1993) concluded that rate of recruitment and consequently size of breeding population are regulated by effects of variable predation on nest success (see also Jönsson 1991). Predation by raptors on wintering grounds is also a significant factor (see Behavior: predation).