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Eskimo Curlew

Background

1.1 Description

The Eskimo Curlew (Numenius borealis) is a small curlew with a slender, slightly decurved bill and little to no eye-stripe (Gill et al. 1998). The plumage of the bird is warm brown, with a solid brown crown, rusty-yellow belly, and streaking on the sides of the face and neck. The undersides of the primaries are unbarred, the wing linings are pale to rich cinnamon, and the wing-tips cover the tail (Figure 1). Eskimo Curlews weigh 270–454 g. They are 32–37 cm in length and have a wing length of 19–23 cm (Gill et al. 1998). The Eskimo Curlew can be easily confused with other shorebird species, including Whimbrel (N. phaeopus), Little Curlew (N. minutus), Long-billed Curlew (N. americanus), Upland Sandpiper (Bartramia longicauda), Pectoral Sandpiper (Calidris melanotos), and Stilt Sandpiper (C. himantopus). In North America, Eskimo Curlews would most often be confused with Whimbrels. However, Eskimo Curlews are only about half to two-thirds of the size of Whimbrels. Whimbrels also differ noticeably from Eskimo Curlews by having barred primary flight feathers, a well-defined eye-stripe, streaked (as opposed to V- and Y-shaped) markings on their breast and flanks, and an overall greyish appearance, as opposed to the overall cinnamon tones of Eskimo Curlews (Gill et al. 1998).

Figure 1. Eskimo Curlew (adapted from photo by Don Bleitz).

Figure 1. Eskimo Curlew (adapted from photo by Don Bleitz).

1.2 Distribution

1.2.1 Historical Distribution

Breeding Range

Nesting was verified from only two sites, both located in the Northwest Territories: the base of Bathurst Peninsula in the Anderson River area, and the region of Amundsen Gulf / Coronation Gulf / Coppermine River (Figure 2). The birds are also likely to have bred in the Barren Grounds throughout much of the Northwest Territories and Nunavut, possibly in the Yukon Territory and Alaska, and perhaps into the Chukchi Peninsula, Russia (Gollop and Shier 1978; Gollop et al. 1986; Gill et al. 1998).

Figure 2. Known historical (black), probable (dark grey), and potential breeding areas (horizontal stripe) of Eskimo Curlews. Adapted from Gollop et al. (1986) and Gill et al. (1998)

Figure 2. Known historical (black), probable (dark grey), and potential breeding areas (horizontal stripe) of Eskimo Curlews. Adapted from Gollop et al. (1986) and Gill et al. (1998).

Fall Migration

Eskimo Curlews migrated east from known breeding grounds to Newfoundland and Labrador and then south non-stop to South America (Figure 3). In Canada, birds were also occasionally seen in northern Ontario, southern Québec (especially in the Magdalen Islands), New Brunswick, Prince Edward Island, and Nova Scotia during the fall.

Figure 3. Historical migration routes of Eskimo Curlews in North America. Adapted from Gollop et al. (1986) and Gill et al. (1998)

Figure 3. Historical migration routes of Eskimo Curlews in North America. Adapted from Gollop et al. (1986) and Gill et al. (1998).

Winter Range

Most winter records of the Eskimo Curlew are from the eastern pampas of Argentina, although it was also recorded in Uruguay, south-central Chile, and possibly southern Brazil and Patagonia. Eskimo Curlews were also noted on the Falkland Islands (Gollop et al. 1986; Gill et al. 1998).

Spring Migration

Birds likely moved from the pampas of Argentina up the Pacific coast to Peru or Ecuador, then across Central America and the Gulf of Mexico (observed in Costa Rica, Guatemala, and Mexico) to Texas (Figure 3). In Canada during the spring, a few birds were seen in southern Manitoba and Alberta, and it was thought that the species was common in Saskatchewan in some years (Gollop et al. 1986; Gill et al. 1998).

1.2.2 Current Distribution

There have been no confirmed sightings of Eskimo Curlews in the world since the 1960s, and no evidence of nesting has been recorded since 1866. Although “possible sightings” continue to be reported, some of these reports may be misidentification of other shorebirds. From 1945 to 1985, 80 possible sightings of Eskimo Curlews were reported from North America (Gill et al. 1998). The last possible sightings in Canada were a group of three birds in southwestern Manitoba (Waldon 1996) and one bird in southern Saskatchewan (Pollock 1996) in the spring of 1996 (but see Gollop 1997 for comments).

1.3 Abundance

The Eskimo Curlew once numbered in the hundreds of thousands, but declined dramatically in the 1870s to 1890s, after which time it was considered very rare (Banks 1977; Gollop 1988; Gill et al. 1998). No evidence of nesting has been verified for 140 years, and the last specimen obtained was shot in the Barbados in 1963 (Bond 1965). There have been scattered sightings since 1900, primarily during migration (Gollop and Shier 1978; Gollop et al. 1986; Gratto-Trevor 1999). No positively identified Eskimo Curlew nests or birds behaving as if they had nests or young have been found since 1866, even though searches have been carried out in historical breeding ranges in the 1970s, 1980s, and 1990s (Gollop et al. 1986; Obst and Spaulding 1994 as cited in Uriarte 1995; Obst and Spaulding 1994 in Gill et al. 1998). In addition, no Eskimo Curlews were found during extensive searches in historical wintering areas of Argentina and Uruguay in 1992–1993 (Blanco et al. 1993).

Population estimates from the 1970s, 1980s, and 1990s varied from 23 to 100 birds; however, these were based on guesswork (Gollop and Shier 1978; Gollop 1988; Morrison et al. 1994). It is possible that this species has since gone extinct.

1.4 Needs

1.4.1 Biological

Primary foods of the Eskimo Curlew included berries (especially crowberry (Empetrium nigrum) and blueberry (Vaccinium sp.) before the long non-stop flight to South America in the fall) and arthropods (including Dipteran larvae and adults, grasshoppers, beetles, and some intertidal gastropods, isopods, and amphipods). In the prairies in spring, grasshopper eggs and young were a common food (e.g., Rocky Mountain grasshopper (Melanoplus spretus)), as well as other insects, earthworms, and berries (Gollop and Shier 1978; Gollop et al. 1986; Gill et al. 1998).

1.4.2 Habitat

Nesting

Nests were apparently initiated from mid to late June, and eggs hatched from early to mid July. As with most other shorebirds, nests were merely a scrape in the ground. Clutch size was normally four eggs, and young were presumably precocial, as is the case for other North American shorebirds. Eskimo Curlews were presumably monogamous, with incubation shared by both sexes, as for other Numeniini (Gollop and Shier 1978; Gill et al. 1998). Renesting was probably uncommon, and likely only one brood was raised per season. Age of first breeding is unknown but was likely delayed, possibly to three years, as for the Whimbrel (Skeel and Mallory 1996).  

Breeding

Known breeding habitat consisted of upland tundra, the treeless dwarf shrub–graminoid tundra complex (“barrens”), and grassy meadow habitat (including polargrass (Arctagrostis latifolia), Arctic bluegrass (Poa arctica), glaucous bluegrass (P. glauca), glandular birch (Betula glandulosa), and species of sedge (Carex), cottongrass (Eriophorum), and Dryas)of the Northwest Territories (Gollop et al. 1986; Gill et al. 1998).

Migration

The birds used a variety of habitats, both coastal and inland, during autumn migration. They often fed in areas of crowberry, as well as coastal habitats in Labrador, and used ericaceous heath habitat in Alaska, the Northwest Territories, northern Ontario, southern Québec, Newfoundland and Labrador, and the Maritime provinces. In Massachusetts, curlews were found in salt grass, meadows, pastures, old fields, intertidal flats, and sand dunes (Gollop and Shier 1978; Gollop et al. 1986; Gill et al. 1998). During spring migration, curlews were found in tallgrass and eastern mixed-grass prairies, often in areas disturbed by recent burns, as well as areas near water disturbed by grazing bison (Bison bison) and cultivated fields (Gollop et al. 1986; Gill et al. 1998).

Wintering

In the pampas of Argentina, treeless grasslands with ephemeral and permanent wetlands were used. Wetter grasslands and intertidal areas of southern Patagonia were also possible wintering habitats (Blanco et al. 1993).

1.4.3 Limiting Factors and Threats

Hunting

Uncontrolled market hunting was likely the main cause of the decline of this species (Swenk 1915; Bent 1929; Young 1953; Gollop and Shier 1978; Gollop 1988). Eskimo Curlews were considered a delicacy and were selected by hunters. They were easy to hunt in large numbers in the United States and Canada due to their aggregation in large flocks, their lack of fear of humans, and their habit of circling back within gun range when some members of the flock were shot (Gratto-Trevor 1999). Market hunters in the Great Plains of the United States shot huge numbers each spring, particularly in the late 1870s and 1880s, as numbers of Passenger Pigeons (Ectopistes migratorius) decreased (Gill et al. 1998). In some areas, an estimated 2000–5000 birds were shot in less than a few days (see review in Gill et al. 1998). In fall, thousands of Eskimo Curlews were killed in Labrador, and in some years many thousands were killed in New England, especially Massachusetts, when birds were forced to land as a result of storms. Because only a few young are produced per pair per year and they likely did not breed as yearlings, hunting of this magnitude could have had profound effects on overall numbers (Gratto-Trevor 1999). Research has shown that even slight changes in annual survival can have large effects on population stability, much greater than the effects of large decreases in productivity (Hitchcock and Gratto-Trevor 1997).

Habitat Loss and Degradation

Although market hunting may have been a main initial cause of the decline of the Eskimo Curlew, changes in its habitat at spring migration staging sites and in wintering areas may have contributed to its decline and prevented its recovery (Gollop et al. 1986; Bucher and Nores 1988; Gill et al. 1998). During the second part of the 19th century, North American prairies were converted to cropland, and prairie fires that had been crucial to the maintenance of grasslands were suppressed (Samson and Knopf 1994; Gill et al. 1998). In addition, changes in farming practices, including planting of winter wheat crops, resulted in even less habitat being available (Davis 1976). Reduction of appropriate feeding habitat may have further concentrated the birds in restricted areas and facilitated hunting (Gill et al. 1998). Conversion of grasslands to croplands also resulted in a decrease of an important food source -- grasshopper egg pods and young (Woodard 1980; Gill et al. 1998).

In the late 1800s to early 1900s, rapid agricultural development occurred in Eskimo Curlew wintering habitat in the pampas of South America. However, this was likely too late to have played a role in the curlew’s population decline (Canevari and Blanco 1994), although it may have prevented any population recovery.

Other Threats and Limiting Factors

Although the Rocky Mountain grasshopper was not the exclusive food of migrating Eskimo Curlews, localized irruptions of this grasshopper species were thought to be important in providing an important spring food source (Gill et al. 1998). The Rocky Mountain grasshopper went extinct in the 1900s, which may have partially contributed to the decline and/or failure of recovery of the Eskimo Curlew.

Another possible contributing factor to the curlew’s demise is the aggressive Whimbrel, which benefited from the overall decline of Eskimo Curlews and completely displaced curlews on Bathurst Peninsula, Northwest Territories (Gollop et al. 1986).

Other factors that may have contributed to the decline of this species include poisoning (e.g., pesticides), storms during transoceanic migration, climate change, drought, and volcanic eruptions that reduced solar radiation (Banks 1977; Gill et al. 1998). These are speculative, however, and there is little information on whether such factors affected Eskimo Curlew populations.

Although the primary causes of the rapid decline in this species are believed to be overhunting and habitat change, the bird’s failure to recover was likely a combination of low population numbers, continued loss of habitat, and conservative life history traits. The Eskimo Curlew likely had a low reproductive rate, producing four-egg clutches that would have been subjected to the vagaries of Arctic weather and predators (Gill et al. 1998). In addition, Eskimo Curlews were likely a long-lived species, as are other Numeniini, and therefore the population would have been sensitive to factors affecting adult survivorship and productivity (Gill et al. 1998). Furthermore, the curlew’s highly social behaviour and its reliance on specific habitats during restricted periods likely made it more susceptible to overhunting. Finally, the Eskimo Curlew’s migration was long and demanding (>14 000 km one way), and the birds relied on relatively few traditional stopover sites, which have since been degraded.

1.5 Critical Habitat

Critical habitat is defined in the Species at Risk Act of Canada as “the habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species” [Subsection 2(1)].

There is very little information on the breeding, staging, or migratory habitat necessary for the recovery or survival of the Eskimo Curlew; therefore, identifying critical habitat for the Eskimo Curlew is not possible at the current time.

1.6 Protection

Eskimo Curlews have been protected since the early part of the last century under the Canadian Migratory Birds Convention Act, 1994 (originally enacted in 1917) and the United StatesMigratory Bird Treaty Act of 1918. All shorebirds have been protected by law since 1927 in Buenos Aires Province, Argentina. Eskimo Curlews are covered under the 1936 Migratory Birds Convention between the United States and Mexico and are included in the United States Endangered Species Act of 1973. They are also covered under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) and the Convention for the Conservation of Migratory Species of Wild Animals (Bonn Convention), with further protection in non-breeding areas through the 1940 Convention on Nature Protection and Wildlife Preservation in the Western Hemisphere. This species was placed on the U.S. List of Threatened and Endangered Species in 1967 and designated as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1978. As of June 2003, Eskimo Curlews were protected under Canada’s Species at Risk Act.

Portions of the historical breeding range in Canada are protected by the Anderson River Migratory Bird Sanctuary and the Kendall Island Migratory Bird Sanctuary, Northwest Territories. Tuktut Nogait National Park is found within “probable breeding areas,” and Ivvavik and Vuntut National Parks are found within “potential breeding areas.” There is also a record of a migratory Eskimo Curlew in Prince Edward Island National Park. Eskimo Curlews found within the boundaries of Canadian national parks or other lands administered by the Parks Canada Agency would be protected under the Species at Risk Act and the Canada National Parks Act and/or measures and management tools available to the Parks Canada Agency under other legislation.