Long-billed Curlew
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The Long-billed Curlew
(Numenius americanus) is the largest shorebird, and the most southerly breeding curlew, in North America. Once abundant over most of the prairie regions of the United States and Canada, populations of the Long-billed Curlew have declined throughout most of the
species' breeding range since the early 1900s as a result of both overhunting and habitat loss. Long-billed Curlews are currently on the
Blue List of species that may be at risk of declining to nonviable population levels in Alberta in the event of further reductions in population, habitat, and/or provincial distribution.
The breeding habitat of Long-billed Curlews is typically described as shortgrass or
mixedgrass native prairie but varies from moist meadows to very dry grasslands. Within certain parameters, curlews appear to be somewhat flexible in their breeding habitat preferences. In general, Long-billed Curlews prefer to nest in areas with large open expanses of relatively low vegetation. Curlew foraging efforts are hampered in years in which weather conditions resulted in abundant thick, standing-dead vegetation.
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Extensive cultivation may eliminate
Long-billed Curlews from an area. However, curlews will occasionally breed in agricultural land
or in tame pastures planted with Crested Wheatgrass. Within Alberta, Curlews also use tame pastures but at somewhat lower densities than in native habitats. It has been suggested that some of the breeding records in cultivated land may, in fact, represent adults tending broods that were hatched in native grasslands. Agricultural land used by breeding Curlews typically has a similar vertical profile to that of native prairie and is usually adjacent to native grassland.
Moderate livestock grazing tends to maintain the low vegetation profile curlews require for breeding.
Grazing regimes that are compatible with maintaining preferred curlew habitat likely vary between regions depending on soil and moisture conditions. Relative height of vegetation may be an important habitat feature that influences the ability of curlews to detect and avoid predators. Although the effect of
habitat fragmentation on curlew habitat selection and breeding success are unknown, the species' current distribution in southwestern Saskatchewan and southeastern Alberta suggests that it prefers large tracts of habitat.
The availability of brood-rearing habitat is another important component of habitat selection by Long-billed Curlews. Shortly after the eggs hatch, adult curlews move their broods to areas where denser vegetative cover
is available. One brood was known to have moved more than 6
kilometres in a six-day period. These areas of denser vegetation may be important for reducing the chances of brood loss caused by predation.
In Alberta, the Long-billed Curlew breeds within the Grassland Natural
Region. Specifically, curlews are most often detected in fescue grasslands, native mixed grasslands, and
sandhills. From a limited number of surveys, maximum breeding densities of curlews occur in moderately grazed mixed grasslands with sandy loam soil. Presumably, land under moderate grazing regimes provides both areas of low, uneven vegetation required for nest-sites and areas of denser vegetation required for brood-rearing.
Habitat requirements during migration within the province appear to be less critical than breeding habitat requirements. During spring migration, Long-billed Curlews are most often observed in upland prairie, stubble, and fallow fields and they also frequent sloughs and runoff ponds during this time. During fall migration and staging, the species is often sighted near bodies of water, such as lakeshores and river valleys.
Conservation and management of the Long-billed Curlew in Alberta relies upon the maintenance of the remaining native grasslands and
sandhills, which the species uses as breeding habitat. The effects of habitat fragmentation and degradation on curlew populations are poorly understood. An understanding of the species' breeding biology is also key to successfully managing Long-billed Curlew populations so that the relative values of habitats used within the province can be determined.
Long-billed Curlews arrive in southern Alberta between April 13 and 24. Territory size varies from 6 to 20 hectares and pairs often return to the same territories in subsequent years. Male curlews tend to return to their natal area for breeding.
Long-billed Curlews are a late-maturing, long-lived species with low reproductive output. Females lay only one clutch each breeding season and only one case of a re-nesting attempt following nest failure has been recorded.
Nests are built in May in a scrape excavated in the ground and are lined with grasses, straw, and plant stems.
Clutch size is usually four eggs, although three- and five-egg clutches are possible. The eggs are olive-buff and are evenly spotted with brown or olive
and usually laid on alternate days resulting in a full clutch taking 4 to 7 days to complete.
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Young Long-billed Curlews are precocial (able to walk and feed themselves shortly after hatch) and hatch
at the same time. Adults lead their chicks to areas of dense vegetative cover shortly after hatching where invertebrates, such as grasshoppers, constitute the majority of the diet for both adults and young. Adult curlews may also feed upon
small amphibians. Major predators on curlew eggs include: Coyotes, Black-billed Magpies, Bullsnakes, Common Ravens, and Badgers. In addition to these predators, curlew chicks are also vulnerable to predation by Ferruginous Hawks, Swainson's Hawks, and Great Horned Owls.
Long-billed Curlews rely upon the cryptic colouration of their plumage and eggs to avoid predation and will crouch low on the nest in the presence of potential avian predators. The effectiveness of this crypsis may be enhanced when breeding territories are located within large tracts of unfragmented habitat. Adult curlews actively defend their eggs and young by feigning injury to lead predators away, and by calling and diving at predators. Non-incubating curlews often assist neighbours in attempts to drive predators away. Curlew breeding territories are frequently clumped in loose aggregations and it has been suggested that this aids in predator defense.
Like many species in which both parents incubate the eggs, the female Long-billed Curlew often abandons the brood 2 to 3 weeks after hatching. Thereafter, the male cares for the young until they
are old enough to survive on their own -- generally 41 to 45 days after hatching. In July and August, adults and juveniles join
post breeding flocks prior to migration and, by the end of August, Long-billed Curlews leave Alberta.