Demography and Populations

Age At First Breeding; Intervals Between Breeding

Age at first breeding unknown. Many individuals in largely gray, Basic plumage (likely to be subadults; Blanco et al. 1992) appear in s. Brazil during breeding season (Belton 1984), suggesting that they do not breed until ≥2 yr old, as known in other shorebirds (Johnson 1979). On the other hand, some Basic-plumaged knots of unknown age arrive at spring-migration staging sites in Delaware Bay in U.S. and can constitute as much as 3–4% of the individuals remaining at end of May (BAH).

Generally annual intervals between breeding, but may skip some years when snow conditions are unfavorable (Tomkovich and Soloviev 1994). Return rates of color-banded individuals at a spring-migration staging area at Delaware Bay indicate that most adults migrate north each year. Little if any information to suggest that many Red Knots of breeding age remain in southern latitudes during boreal summer (Blanco et al. 1992).

Clutch

Almost always 4 eggs (see Breeding: eggs, above), the postulated ancestral sandpiper clutch size (Maclean 1972). No information available on relative size of initial versus replacement clutches.

Annual And Lifetime Reproductive Success

No information on lifetime reproductive success.

On Ellesmere I., 3 of 7 nests were destroyed (Nettleship 1974); on w.-central Ellesmere I., 24 of 27 eggs hatched in 7 nests (Parmelee and MacDonald 1960). No information on annual variation of hatching success.

On the basis of numbers of juvenile rufa recorded during 20 summers in Massachusetts (BAH), annual breeding success varies greatly. Boyd (1992) shows a striking relationship between annual production of young C. c. islandica and Arctic snowcover conditions in spring, as known in other northern-breeding sandpipers (Cooper 1994). Dur-ing 3 summers in Siberia, Tomkovich and Soloviev (1996) found 40% lower nesting densities of C. c. canutus in a 14-km²area in the year with latest snowmelt.

Number Of Broods Normally Reared Per Season

One; multiple broods unknown.

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence

Insufficient information for meaningful interpretation. Highly variable among years (Tomkovich and Soloviev 1996).

Few published data. Using Model 2 of Program Jolly (Pollock et al. 1990), BAH estimated annual survivorship rates among knots returning to Delaware Bay during 3 yr at 0.66, 0.87, and 0.51 (aver-age 0.68). Boyd (1992) suggested that annual adult survivorship of C. c. islandica varies substantially between years.

Life span unknown. Longest-living C. c. rufa individuals known were banded as adults on New Jersey coast of Delaware Bay: One banded during May 1980 was resighted on same coast during May 1990, a second banded as adult in May 1986 was recaptured on same bay in May 1997, and a third banded in May 1987 was captured on Delaware Bay in May 1999 and seen again there in May 2000 (BAH).

An epizootic resulted in large-scale mortality of Red Knots along west coast of Florida in Dec 1973 and Nov 1974; caused by a protozoan parasite, most likely an undescribed sporozoan species (Woodard et al. 1977). Other mortality in Florida has been attributed to the blood parasite Plasmodium hermani (Forrester and Humphrey 1981). High mortality of knots in s. Brazil was caused by Acanthocephala spp. (A. Baker pers. comm.).

Adventitious molt in Red Knots may have been caused by a mallophagan parasite (Mallophaga: Menoponidae) in feather shafts (Taylor 1981).

See Behavior: predation, above, and Disease and body parasites, above.

Natal Philopatry

No evidence to suggest that young return to breed at natal sites (Tomkovich and Soloviev 1994).

Fidelity To Breeding Site, Migration Stopovers, And Winter Home Range

Males are highly faithful to breeding territories from year to year. In Siberia, at least 10 of 14 color-banded males returned to territories between 1990 and 1991; only 1 female returned to same site between years; density was relatively consistent from year to year (Tomkovich and Soloviev 1994, 1996).

This species is quite faithful to specific migration staging sites. Harrington et al. (1988) found maxi-mum counts of roughly 2,000 adults at a fall staging site at Scituate, MA, during 1980s; virtually all of the color-banded birds resighted there had origin-ally been marked there. Few were found from other banding locations, even though more individuals had been marked at other locations.

During spring, by contrast, individuals banded in previous autumns at Scituate were found on shores of Delaware Bay in similar proportions as those originally banded on Delaware Bay (see Harrington et al. 1988 for information on band class sample sizes and resighting rates).

Banding also showed that individuals repeatedly returned to wintering areas in Florida, but that there was no mixing of Red Knots between Floridian and Argentine wintering areas (Harrington et al. 1988).

Dispersal From Breeding Site Or Colony

Distances between annual nest sites of 6 males in Russia ranged from 95 to 405 m (mean 302 m ± 140 SD; Tomkovich and Soloviev 1994).

Home Range

No information.

Numbers

Estimates of population size exist for C. c. canutus (512,000 individuals; Meltofte et al. 1994); C. c. islandica (500,000 [Meltofte et al. 1994]; 430,000 [Piersma and Davidson 1992]); C. c. rufa (adults, 143,700 ± 13,600 SD; BAH); and C. c. rogersi (160,000–200,000; Barter et al. 1988). No estimate for C. c. roselaari .

Trends

Regression analysis of peak counts (maximum 96,000, or >60% of estimated population) made during aerial surveys of Red Knots on Delaware Bay between 1986 and 1992 showed non-significant population decline for rufa (Clark et al. 1993). Analysis of counts made in 1970s, 1980s, and early 1990s from e. Canadian migration stopover sites also showed nonstatistically significant de-clines (Morrison et al. 1994). Annual estimates of adult population size based on resighting ratios of color-banded individuals during spring on Delaware Bay between 1981 and 1990 also showed no clear trend (BAH). C. c. islandica populations have declined considerably since the 1970s (Meltofte et al. 1994).

No information.