Long-billed Curlew
Limiting Factors
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Within Alberta, the Long-billed Curlew's breeding range
is restricted to the Grassland Natural Region and availability of suitable nest-sites and brood-rearing
habitat likely limits the distribution and abundance of the
species within the province.
Long-billed Curlew populations are naturally slow growing which may make them particularly vulnerable to reductions in habitat or population. There is some indication that
drought conditions may reduce
Long-billed Curlew breeding success by reducing the abundance of areas of dense vegetation needed for brood-rearing. It is speculated that if such conditions persist, the result might be a decline in population. Management of Long-billed Curlews in Alberta should take into consideration the possibility of future periodic droughts and the effect this may have on the population levels.
Like other ground-nesting species, Long-billed Curlews also face high rates of nest and chick predation. Human-related influences, such as habitat use,
loss and fragmentation, may increase the effect natural limiting factors have on the Alberta curlew population.
Loss of habitat, as a result of the conversion of native prairie to cropland and urban development, has been identified as the single greatest cause of past declines in curlew populations. Since the 1900s, the distribution of curlews in North America has contracted along the eastern grasslands, likely resulting from habitat loss. Within Alberta, an estimated two-thirds of the original grasslands have been lost to cultivation. The remaining grasslands are under increasing pressure, especially with large-scale irrigation projects enabling cultivation in arid areas. In general, crop farming is detrimental to curlew habitat, while ranching activities designed for long-term maintenance of the grasslands sustain curlew breeding habitat.
Land under moderate grazing regimes presumably provides the habitat heterogeneity curlews require for both successful nesting and brood rearing. Moderate livestock grazing appears to enhance curlew breeding habitat, but heavy grazing, particularly during droughts, may eliminate important brood-rearing areas. Furthermore, egg loss due to trampling by livestock may increase with increasing stocking rates.
The effects of grazing on curlew breeding habitat appear to vary across the species' range. This variation may reflect differences in moisture or vegetation and/or variation in the classification of grazing regimes between regions and observers. Whereas some curlews have been reported to use cultivated land for breeding activities, it has not been documented whether these birds breed with the same success as those in native habitat.
Pesticide use may also influence curlew breeding success, either through direct ingestion of the chemicals or through a reduction in the invertebrate prey that constitute the curlew diet. Threats to the
wetlands that serve as wintering habitat, such as the Pantanal Wetlands in South America, may also adversely effect Alberta's population of curlews.
Initial declines in Long-billed Curlew populations occurred as a result of
over hunting in the late 1800s and early 1900s. While curlews are no longer a game or commercial species, their large size, conspicuous mobbing behaviour, and tenacious incubation behaviour may make them vulnerable to being shot illegally. Road and petroleum pipeline construction may result in both habitat loss and habitat degradation and human activity and disturbance can result in nest desertion.
Other human-related causes of nest failure include predation of adults, eggs, or young by domestic cats and dogs, and nest desertion following the trapping of incubating birds on the nest.