Demography and Populations

Measures Of Breeding Activity

Age At First Breeding; Intervals Between Breeding

Over southern parts of range, probably routinely breed as yearlings. On Queen Charlotte I., British Columbia, routinely breed as 1-yr-olds; 91% of 68 breeders originally banded as chicks were recaptured as yearlings (Cooper 1993). Yearlings comprised 19–20% of breeding population. At least 1 yearling bred in n. Manitoba (C. Gratto-Trevor pers. comm.).

Clutch Size

Almost always 4 eggs (Philipp 1925, Jehl 1970, Jehl and Smith 1970, Miller 1979a, Cooper 1993), assumed ancestral sandpiper clutch size (Maclean 1972). No difference in clutch size between yearling or older females (Cooper 1993). Replacement clutches often contain 4 eggs but are more likely to have 3 eggs than initial clutches (Cooper 1993).

Annual And Lifetime Reproductive Success

No data on lifetime reproductive success. Annual success dependent mainly on predation rates on eggs and effects of weather. On Sable I., Nova Scotia, 93% of fully incubated eggs hatched, 95% of hatched chicks left nest, and 40% of chicks leaving nest fledged (Miller 1983a). Definitive clutches that hatched produced average of 2.1 chicks leaving nest and 0.9 fledglings (Miller 1983a). On Queen Charlotte I., 57% of clutches hatched and 76% (n=103) of the broods produced at least one fledgling. Mean of 2.23 fledglings produced from successful broods. Nineteen of 46 (41%) broods that produced fledglings during 1987 produced at least one yearling (mean = 1.37) that returned to breed in 1988. Assuming 90 breeding pairs during 1987-88, population produced 1.92 chicks/pair, 1.02 fledglings/pair and 0.29 yearlings/pair per yr (1987 only; Cooper and Miller 1997). One brood produced annually, except for 1 case on Queen Charlotte I. where pair produced second brood after first brood was lost 1–3 d after leaving nest (Cooper 1993).

At Churchill, Manitoba, 80% of 219 eggs laid in 56 nests survived to hatch (3.1 eggs hatched/female). Eggs that did not hatch were deserted (1 clutch), did not hatch (3 single eggs in 3 clutches), infertile (11 eggs in 5 clutches), preyed on (19 eggs in 6 clutches), or destroyed by weather (6 eggs in 2 clutches). Hatching success not related to density of nests (Jehl 1971).

Life Span And Survivorship

Few data available. Oldest known individual a male at least 16 yr old that bred on Sable I. (Miller and McNeil 1988).

Disease And Body ParasitEs

Chewing lice (Carduiceps zonarius) found on 92% of 25 fall migrants in n. California (mean 3.9 ± 0.6), distributed nonrandomly on individuals (Hunter and Colwell 1994).

Causes Of Mortality

Susceptible to avian botulism (Adams et al. 2003). See Behavior: predation; also Annual and lifetime reproductive success (above).

Range

Natal Philopatry

At least some chicks return to breed near natal site, but nest farther away from it than parents tend to do (JMC).

Fidelity To Breeding Site And Winter Home Range

Breeding males and females have strong tendency to return to previous nesting territories (Jehl 1973, Miller 1983a, Cooper 1993), a trend common in most scolopacids (Miller 1977). Males nest in about same place between and within years, as do females that mate with their mate from previous year. Females that change mates, however, nest farther away from previous nesting area (Miller 1979a, JMC).

Some fidelity to wintering and migratory staging areas. In California, 26% of adults and 22% of juveniles returned next year (Page 1974). In interior Venezuela, 4 of 75 banded birds were recaptured on same 5-ha site 1 or 2 yr later (Thomas 1987).

On Magdalen I., Quebec, 1.9% of 674 banded adults recaptured following year on southward migration (McNeil and Burton 1973). At Cheyenne Bottoms, KS, 1.7% of 9,034 banded birds recaptured in later years (Martinez 1979).

Dispersal From Breeding Site Or Colony

Few data, but thought to be very little dispersal of experienced breeders between years (Miller 1983a).

Home Range

No data available.

Population Status

Numbers

Difficult to census because of confusion with Western and Semipalmated sandpipers, with which Least Sandpiper frequently associates in mixed flocks. Often found to be eighth to tenth most abundant migrant shorebird in Atlantic Coastal wetlands (e.g., Burger 1984); third most captured fall migrant shorebird in James Bay, Canada (Morrison 1978); second most frequently captured shorebird at Cheyenne Bottoms (Kansas) and Surinam after Semipalmated Sandpiper (Martinez 1979, Spaans 1979); third most abundant spring migrant and eighth most abundant fall migrant shorebird in Saskatchewan (Colwell et al. 1988).

Fall counts in North America: eastern USA 70,900, eastern Canada 31,000, Interior Flyway 322,700, and western USA and Baja California 150,000, totaling 574 600, plus a further 11 000 in Alaska. Spring counts (1971-98) generally lower: eastern USA 37,700, central USA 124,600, and Pacific (California wetlands) 48,000, totaling 210,300 (Morrison et al. 2001b).

In Prairie Pothole Region 2002-03, an average of 145,642 ± 34,152 (SE) birds during northward and 96,473 ± 24,022 (SE) during southward migration. Assuming 7-day residency period for each season, an estimated 634,600 and 193,000 birds pass through in spring and fall, respectively (Skagen et al. 2008). Assuming that the true number lies 1 SE below the mean, totals are 485,000 in spring and 144,900 in fall. Using an estimate of >600,000 for migrants passing through the interior in spring and using the maximum spring counts of 37,000 for the Atlantic cost and 48,000 for the Pacific coasts, results in a total population of about 700,000 (Morrison et al. 2006).

On West Coast, a major spring staging area in Alaska is Copper River Delta where 1 flock of 100,000 was reported in May during the 1970s (Isleib 1979). High spring counts farther south include 23,000 at Summer Lake, OR, on 1 May 1987 (Paulson 1993); 5,000–10,000 at Grays Harbor, WA, in Apr (Paulson 1993); and 17,000 in San Francisco Bay, CA, in mid-Apr (Stenzel and Page 1988). Density in Bolinas Lagoon, CA, ranged from 77/100 ha in spring to 389/100 ha in fall (Page et al. 1979), with Oct population of about 2,400 tailing off to about 1,200 in Dec (Page and Whiteacre 1975). In Humboldt Bay, CA, a density of 1,473/100 ha (Gerstenberg 1979). Hicklin (1987) estimated 12,000–19,000 in late summer in Bay of Fundy. In Massachusetts, high spring count of 4,500 at Newburyport (12 May) and fall count of 1,500 at Monomoy (18 Jul) (Veit and Petersen 1993).

In Prairie Pothole Region 2002-03, an average of 145,642 ± 34,152 (SE) birds during northward and 96,473 ± 24,022 (SE) during southward migration. Assuming 7-day residency period for each season, an estimated 634,600 and 193,000 birds pass through in spring and fall, respectively (Morrison et al. subm).

Winter populations difficult to census because individuals do not concentrate in a few areas, as many other species of Calidris sandpipers do, and are usually lumped with other small “peeps” because of inability to identify them during aerial surveys. Although Semipalmated Sandpipers form bulk of small sandpiper populations in n. South America, Least Sandpipers comprise significant, but unknown, percentage of 1.3 million small shorebirds on Surinam coast and 327,000 on coast of ne. Brazil (Morrison et al. 1989). Spaans (1978) estimated 50,000–100,000 wintering on coast of Surinam. In Sinaloa, Mexico, substantial numbers counted in 1993 and 1994: Ensenada Pabellones 300-2,300 and Bahia Santa Maria 2,900-21,600 birds (Engilis et al. 1998). On west coast of Baja California, Mexico, 2,090 birds counted in 1998-93, <1% of wintering shorebirds present (Page et al. 1997).

Few data on breeding densities. Widely scattered over most of range. Estimates include 9 pairs/10 km² on Alaska North Slope (Sage 1974) and 90 pairs/110 ha on Queen Charlotte I. (Cooper 1993). Canadian breeding population estimated to be 50,000–100,000 (Morrison et al. 1994).

Trends

Species of moderate concern, based on decreasing population trends. Population size, breeding and nonbreeding threats and distributions not of concern (Andres et al. 2006, U.S. Shorebird Conservation Plan 2004).

Populations thought to be stable in w. and central Canada (Morrison et al. 1994); on Sidney Island, British Columbia, non-significant declines reported for 1992-2000 (Butler and Lemon 2001). Significant declines in eastern North America (Morrison et al. 2001a, Morrison and Hicklin 2001, Bart et al. 2006). Annual change on fall migration in eastern Canada between 1974 and 1991 is -3%, and 10-year change is -76% (Morrison et al. 1994).). In Maritime provinces, significant decline between 1974 and 1998, with an annual change of -15.8%. In Quebec and Ontario, non-significant decline; on e. coast of USA, an annual increase of 2.9% (Morrison et al. 2001). Large but non-significant decline in N. Atlantic region (northeast US and southeast Canada), no change in US midwest (Bart et. al. 2007).

Population Regulation

Few data. Predation on breeding and non-breeding grounds can be significant (see Behavior: predation). On Sable I., breeding population may not be maintaining itself because of predation by Herring Gulls (Miller 1983a).

Local manipulations of habitat on Queen Charlotte I. have shown that Least Sandpiper can quickly colonize good breeding habitat (Cooper 1993), but forest succession is reducing available nesting habitat in prime nesting area, with numbers of breeders likely declining (JMC).

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