Conservation and Management

How should conservation priorities for knots be determined? The U.S. Shorebird Conservation Plan (Brown et al. 2000) outlines numerous issues but does not focus specifically on Red Knots. Arctic-breeding shorebirds like knots have low fecundity and are subject to substantial annual variation in breeding productivity. On the other hand, they have relatively high survival rates (Boyd 1962). Modeling (Hitchcock and Gratto-Trevor 1997) suggests that population sizes of arctic sandpipers with these characteristics are strongly influenced by adult survival rates.

Little is known of what factors most influence survivorship of Red Knots. Pfister et al. (1998) found circumstantial evidence for extensive, differential survivorship of sandpipers related to their body condition at migration staging areas. Page and Whitacre (1975) found strong influences on survivorship of sandpipers at a California wintering location, and Soikkeli (1970) showed sandpiper mortality higher in winter than during breeding.

It is clear that high fractions of Red Knot populations can occur together at a small number of nonbreeding locations (see below), leaving popu-lations vulnerable to loss of key resources. On the basis of band ratios obtained at Delaware Bay, BAH (unpubl.) estimated that adult rufa population in spring 1989 was 152,900 ± 50,300 SD. During same spring, Clark et al. (1993) estimated 94,460 knots on Delaware Bay coast during a peak migration count.

Thus, somewhere between 42 and 92% of the entire adult rufa population was present on the bay on a single day; allowances for turnover would make the seasonal percentage values even higher. It thus seems clear that the adult knot population is vulnerable to events or practices that affect resources that attract them to the bay; there is no information to show what would transpire should these re-sources be lost to knots’ use. Piersma and Baker (2000) suggest that “the future of many species of migratory shorebirds depends on adequate conservation of . . . [key] wintering and staging sites.” An effort toward this end was begun in 1985 by the Western Hemisphere Shorebird Reserve Network (see Management, below).

Shooting And Trapping

Heavily hunted for both market and sport during second half of nineteenth and first quarter of twentieth centuries. Mackay (1893) noted that market hunters, working at night by firelight, sent a single shipment of knots from Cape Cod to Boston, MA, that filled 6 barrels. If each barrel held 60 dozen knots, then perhaps more than 4,000 knots were taken in a single night. Bent (1929) noted that excessive shooting and market hunting had reduced the species to “a pitiful remnant of its former numbers.” It is unclear today whether the population has regained its historical numbers. It is clear, however, that numbers on the Massachusetts coast are far lower today than they were when Mackay (1893) wrote his accounts.

Band recoveries indicate that knots are killed commonly for food in some regions of South America, especially in the Guianas (BAH). They also are shot for sport in Barbados. The overall take from these activities is unknown, but information from band recoveries (n = 17) in the Guianas (BAH) hints that the take may be substantial.

Pesticides And Other Contaminants/Toxics

No information.

Ingestion Of Plastics, Lead, Etc

No information.

Collisions With Stationary/Moving Structures Or Objects

Shorebirds, including Red Knots (Piersma et al. 1994), occasionally collide with stationary objects (e.g., McNeil et al. 1985).

Climate Change

Global warming may have especially strong impacts on this species. Anticipated climate change will be greatest at polar and temperate latitudes, where Red Knots breed and winter, respectively. All known major migration staging sites, and most of the major wintering range, are on temperate coastlines of both the New and Old World, where sea level change is predicted to be greatest.

Degradation Of Habitat

Tendency to concentrate at traditional migration staging sites and wintering areas may render populations vulnerable to loss of strategic habitats critical to the well-being of their populations (Myers et al. 1987). According to studies by Harrington et al. (1989), which evaluated the relative concentration of 24 shorebird species at migration staging sites, Red Knots were the most heavily concentrated of all shorebirds, with 98% in the spring and 97% in the fall concentrated at key sites, virtually all of which were coastal locations. Similarly, during aerial surveys of South American coastlines where Red Knots spend the boreal winter, Morrison and Ross (1989: Vol. 1) tallied roughly 76,000 individuals, >50% at a single bay, Bahía Lomas on the n. Chilean coast of Tierra del Fuego. Concern is growing that vastly increased harvesting of horseshoe crabs during 1980s and 1990s on mid-Atlantic Coast of U.S. will hinder use of Delaware Bay as a critical migration staging area by Red Knots during spring (Tsipoura and Burger 1999, Piersma and Baker 2000).

Baker (1992) and Baker et al. (1994) noted that levels of genetic variation in Red Knots and most other calidridine sandpipers are seriously depleted, presumably because of reduced population bottlenecks during Pleistocene (or later) glaciations; species that have lost genetic variability may be more vulnerable to extinction, notably through effects on development, growth rate, and survival.

Direct Human/Research Impacts

See Management, below.

Conservation Status

Not listed as Endangered or Threatened, but listing was under consideration as this account was being written.

Measures Proposed And Taken

A key management goal in shorebird conservation efforts in the New World is to identify important migration staging sites and wintering areas of these birds and to work for their voluntary inclusion in the Western Hemisphere Shorebird Reserve Network (WHSRN). At many of the WHSRN sites, local conservation initiatives are focused on better protection of key habitats of Red Knots. One such area is Delaware Bay, which is included in WHSRN. Similar initiatives are under way elsewhere in the world, notably including some international treaties, such as the Ramsar Convention (Anonymous 1971).

Management efforts to protect Delaware Bay staging sites involve local, state, and federal agen-cies. Major initiatives include reduction of risks of industrial and maritime accidents to knots and the resources they use. A greatly increased commercial harvest of gravid, female horseshoe crabs during 1990s also is thought to be threat to knots (Tsipoura and Burger 1999). Crab eggs are a primary food resource for Red Knots at Delaware Bay and may have been less abundant in the late 1990s than in 1980s, owing to greatly increased harvests of female crabs (S. Shuster pers. comm.).

Disturbance associated with collection of gravid crabs on beaches also flushes knots. Chronic human disturbance at marine and estuarine nonbreeding habitats is thought to reduce suitability of habitats for Red Knots (Pfister et al. 1992, Burton et al. 1996). Modeling of the energetic costs of chronic distur-bance to knots also indicates that such disturbance at migration sites could affect the species’ ability to gain fat at migration staging sites (BAH). A variety of federal and state regulatory initiatives to limit the horseshoe crab harvest are under consideration, and several were implemented in New Jersey and Delaware in the late 1990s.

Elsewhere in the world, key food resources of Red Knots also are demonstrably vulnerable to human activities—e.g., shellfishing activities depleting bivalve populations and destroying important habitats for a decade or more (Piersma and Koolhaas 1997). In South America, wintering and migration staging areas are also vulnerable to human population growth and economic expan-sion. Through WHSRN, measures to protect roost-ing sites at a key wintering area near Rio Grande, Argentina, are under consideration. In Río Negro Province, WHSRN-proposed measures to protect a key migration staging area near San Antonio Oeste also are being considered by Argentine authorities. In Rio Grande do Sul, the southernmost state of Brazil, a major migration staging area of knots at Lagoa do Peixe—also a WHSRN site—has been established as a national park by the Brazilian federal government. During southward migration, substantial fractions of the rufa population visit coasts of Suriname; 3 major sections of this national coastline are included in the WHSRN.

Effectiveness Of Measures

Most of the measures described in the preceding section were designed to prevent population declines among shorebird populations by protecting key resources needed during winter and migration. North American populations of Red Knots have fluctuated substantially since WHSRN was established in the 1980s (BAH), making it difficult to document statistically significant population changes. However, significant and substantial declines have been detected in sev-eral other species that share nonbreeding habitats with knots (Howe et al. 1989, Morrison et al. 1992).