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Demography and Populations
Measures Of Breeding Activity
Age At First Breeding; Intervals Between Breeding
Little information. Birds banded as chicks not seen in natal area as yearlings or as 2-yr-olds; 2 of 71 birds banded as chicks nested in natal area at age 3 yr (Skeel 1983). Normally breed every year after first attempt; never >1 brood per season.
See Appendix 1 . Usually 4 eggs (78% of 287 clutches), sometimes 2 (8.0%) or 3 (13.9%). Some nests with <4 eggs have lost egg(s) due to predation (Skeel 1983). Complete clutch of 2 eggs (Daukes 1933) and 3 eggs (Skeel 1976a) documented; also 5 eggs (Witherby et al. 1940), unless this was a case of intraspecific dumping. In Manitoba, average clutch size 3.70 eggs (n = 287; see Appendix 1). Size of replacement clutch unknown.
Annual And Lifetime Reproductive Success
Hatching success (eggs laid that hatched) and nest success (pairs successfully hatching ≥ 1 chick) vary across range and time (Appendix 1). Of eggs failing to hatch in Manitoba, 55 predated, 3 infertile, 1 squashed (n = 220; MAS); 28 predated, 3 infertile, 3 failed to hatch, 4 destroyed by bad weather (n = 78; Jehl 1971); 140 predated, 4 abandoned (n = 279; W. Lin pers. comm.). Survival of eggs and/or nests to hatching varies with habitat and proximity to other mobbing species (see Behavior: predation, above). Also varies among years: at Churchill, Manitoba (MB), observed hatching success and nest success were 62 and 64%, respectively, in 1994 versus 31 and 30%, respectively, in 1995 (W. Lin pers. comm.).
Few data on survival of chicks to fledging for North America. Over a 4-yr period in w. Alaska, <13% of nests fledged young (n = 24); availability of invertebrate prey may affect productivity in some years (B. McCaffery pers. comm.). On Shetland Is., U.K. (Grant 1991a, b), about 41% of pairs (n = 85) fledge ≥1 chick, producing 0.75–0.91 fledged young/breeding pair; moreover, about 32% of hatched chicks (n = 232) fledge; 60–70% of chick mortality occurs in first 7 d, >80% in first 14 d; survival to fledging correlates sinificantly with clutch mean hatchling weight. No information on lifetime reproductive success.
Life Span And Survivorship
Disease And Body Parasites
Causes Of Mortality
See Behavior: predation, above. No data on mortality due to exposure.
Initial Dispersal From Natal Site
Few data. Two birds (both males) of 71 banded as chicks recovered 3 yr later nesting about 1,000 and 1,630 m, respectively, from their hatching sites in natal hummocky taiga habitat (Skeel 1983).
Fidelity To Breeding Site And Winter Home Range
In Manitoba, in habitat with high nesting success, pairs usually re-establish near or on territory of previous year; do so less often where nesting success has been lower (Skeel 1983). Twenty of 22 adults recovered over 4 yr remained habitat true, renesting 156 ± 15.7 (SE) m (range 41–376, n = 20) from their previous sites; 2 (females) renested 5.3 and 6.6 km away, respectively, changing from sedge tundra to hummocky taiga habitat. A female recaptured after 10 yr nested <20 m from her previous site (Skeel 1976b). In Mackenzie River Delta, Northwest Territories (NWT), 6 of 9 nests were <400 m from a previous year’s nest (Dickson et al. 1989). In w. Alaska, at least some birds return to territory of previous year (B. McCaffery pers. comm.). On Shetland Is. (Grant 1991a), fidelity to study site is significantly higher for males (87%) than for females (68%).
Little information on fidelity to wintering areas or migratory staging areas. One bird banded in Panama in 1979 was resighted on same intertidal territory 7 yr later (EPM).
Dispersal From Breeding Site Or Colony
Few data; see Initial Dispersal from Natal Site, above.
Little information. One adult observed about 7 km from its nest site during nesting period (MAS).
Numbers And Trends
Total population of N. p. hudsonicus was estimated at 25,000–100,000 in 1993; no definitive information on trends (Rose and Scott 1994). Aerial surveys in South America yielded estimate of 25,000 for a continentwide wintering population (Morrison and Ross 1989a). International Shorebird Survey data during migration at Atlantic Coast stopovers indicated significant decline from 1972 to 1983 (small sample-size, possibly an anomaly; Howe et al. 1989); analysis of Maritimes Shorebird Survey data showed no significant upward or downward trend from 1974 to 1991 (Morrison et al. 1994a).
Breeding density varies with habitat. In North America, 0.005–0.11 pairs/ha; in Old World, 0.003 to about 0.3 pairs/ha. In Manitoba, 0.11 pairs/ha in hummocky taiga habitat, 0.036 and 0.028 pairs/ha in sedge tundra and heath tundra habitats, respectively (Skeel 1983). In se. Northwest Territories, density of 0.005 pairs/ha over 88 km2of variable habitat (60% of which is suitable for nesting Whimbrels; J. Obst pers. comm.); in Mackenzie River Delta, NWT, 0.015–0.05 pairs/ha in moderately wet sedge/low-centered polygon habitat (Dickson et al. 1989, Gratto-Trevor 1994). In w. Alaska, 0.010–0.016 pairs/ha in dwarf shrub habitats (B. McCaffery pers. comm.). On Shetland Is., U.K., 0.11–0.21 pairs/ha (Grant 1991a); on Faeroe Is., Denmark, about 0.3 pairs/ha (M. Richardson in Grant 1991a); in Finland, 0.003–0.011 pairs/ha (Pulliainen and Saari 1993).
Populations are probably regulated primarily by egg predation and chick mortality; possibly also by climatic factors influencing breeding and mortality.