Mountain Plover (Charadrius montanus)
© Cottonwood Consultants Ltd.: photo: Cliff Wallis
The Mountain Plover is a medium-sized shorebird resembling a small Killdeer (Charadrius vociferus) without the distinctive neckbands. It has a uniform sandy-brown back and wings, a clear white breast, and whitish underparts washed with buff. Breeding birds have a white forehead, black on top of the head, and a distinctive black stripe from the black bill to behind the eye (Figure 1).
2.2 Distribution and Abundance
The natural breeding range of Mountain Plovers extends throughout much of the western Great Plains of North America (Figure 2), from southern Alberta and Saskatchewan south through Montana, Wyoming, Nebraska, Colorado, Kansas, New Mexico, Oklahoma, Texas (Knopf 1996; Knopf and Rupert 1996), and northern Mexico (Desmond and Chavez-Ramirez 2002). Their winter range is primarily in California, now primarily within the Imperial Valley (Wunder and Knopf 2003), although the species also winters in northern Mexico, southern Arizona, and southern Texas.
Estimates in the 1990s placed the global population as low as 5600 (Morrison 1994; Rose and Scott 1997). Knopf (1996) provided a revised estimate of 8000–10 000 birds for the North American population based on a doubling of the number (3346) of birds found during winter counts in California in 1994 plus an estimated wintering population of 1000–3000 in Texas and Mexico. Using more refined methodology for population estimates in Wyoming, Plumb et al. (2005a) revised the continental population estimate to 11 000 –14 000 birds.
As of the year 2000, the Mountain Plover was globally ranked as G2 (imperilled) (NatureServe 2004). The IUCN (World Conservation Union) Red List of Threatened Species ranks the Mountain Plover as vulnerable (BirdLife International 2004).
2.2.2 United States
Breeding Bird Surveys in the United States indicate a rate of decline of 2.7% per year from 1966 to 2004 (Knopf 1994, 1996; Sauer et al. 2005), suggesting a two-thirds reduction in the population during that period. Breeding Bird Survey results show that the decline in this species from the 1960s to the early 1990s was larger than that of any other endemic grassland bird. Concomitant with the population decline, the breeding range has contracted, especially along its eastern edge.
The species was recommended for protection under the Endangered Species Act in the United States because the population declined at least 3% per year during the 1970s, 1980s, and early 1990s (Knopf 1996). The U.S. Fish and Wildlife Service concluded that listing was unwarranted because threats to the species and its habitat were not as significant as previously thought and were not likely to endanger the species in the near future or throughout a significant portion of its range (USFWS 2003).
In the United States, the species is ranked as N2 (imperilled) for both breeding and non-breeding populations (NatureServe 2004).
The species’ range extends into extreme southern Canada (Figure 3) where it is considered a rare breeder in southern Alberta and Saskatchewan (Godfrey 1986). Wershler (2000) speculated that “During the last two decades there have probably been fewer than 50 adult Mountain Plovers in Canada.” Morrison (2001) estimated the Canadian population to consist of about 10 pairs.Only 44 Mountain Plovers were recorded in Canada between 1874 and 2005 (Knapton et al. 2006).
In Canada, reports of breeding Mountain Plovers have been sporadic. Nests with eggs or adults with dependent young have been found in extreme southeastern Alberta only 16 times in the past 25 years (Wallis and Loewen 1980; Wallis and Wershler 1981; Wershler 1990; Knapton et al. 2006; D. Heydlauf, pers. comm., 2005). There has been one nesting record in Saskatchewan, in 1987 (Gollop 1987a; Wershler 2000). The distribution of records in Canada suggests that there are two main areas of habitation: the Lost River – Wildhorse area of Alberta and the Grasslands National Park area of Saskatchewan (Figure 3).
The species was designated as endangered in Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1987 (Wershler and Wallis 1987); this designation was maintained by COSEWIC following an updated status report in 2000 (Wershler 2000). The reason for the designation is given as follows: “This species occurs in extremely low numbers in Canada; it is dependent on habitats resulting from overgrazing, which are very rare in Canada” (COSEWIC 2002). It was listed as endangered under the Species at Risk Act in 2003. As of 2001, the species was ranked as N1 (critically imperilled) in Canada and S1 (critically imperilled) in both Alberta and Saskatchewan (NatureServe 2004). Saskatchewan’s Conservation Data Centre classifies the Mountain Plover as endangered in the province, and Alberta’s Endangered Species Conservation Committee has recommended that the Mountain Plover be designated as endangered in Alberta.
2.2.4 Populations in Montana(nearest to Canada)
The stable breeding population that is closest to Canada is on a large complex of black-tailed prairie dog (Cynomys ludovicianus) colonies in Phillips and Blaine counties in northern Montana (Olson 1984; Prellwitz 1993; Knowles and Knowles 1997, 2001; Dinsmore et al. 2003). The international border between Montana and southwestern Saskatchewan delineates the northern boundary of these two counties. The number of Mountain Plovers in these two counties was estimated at about 2000 individuals in the mid-1990s (Knopf and Miller 1994; Knowles and Knowles 1998), but Dinsmore et al. (2003) revised this figure downwards to only 700 plovers. The most commonly inhabited area and largest populations of Mountain Plovers in these counties are between 80 and 150 km from the three most commonly used areas in Canada. It should be noted that the areas in Montana immediately adjacent to the Alberta border are intensively cultivated and unsuitable as nesting habitat for Mountain Plovers (Knowles and Knowles 1998; Shackford et al. 1998). The best information currently available indicates that the total population in Montana is approximately 1500 Mountain Plovers (Knowles and Knowles 1998; Dinsmore 2003; USFWS 2003).
2.3 Species’ Needs
2.3.1 Breeding Habitat
Mountain Plovers have a narrow range of habitat requirements (Graul 1980) and are one of only nine bird species endemic to the North American steppe (Knopf 1988). Mountain Plovers breed in areas of flat topography with sparse (15–80% bare ground) and short (<10 cm in height) vegetation (Wershler and Wallis 1987; Parrish et al. 1993; Knopf and Miller 1994; Knopf 1996; Knowles and Knowles 1998).
In Canada, Mountain Plovers have nested in grazed or recently burned areas of native mixed grassland and sagebrush/bentonite flats (Knapton et al. 2006). In one instance, a nest was found in a field of exotic Russian wildrye (Elymus junceus) and native plant species that had been lightly cultivated (Wershler 2000).
Although this species nests in the shortgrass ecoregion, it appears that it is a disturbed-desert species rather than a strict-associate of the short-grass prairie (Knopf and Miller 1994; Plumb et al. 2005b; Knapton et al. 2006). This is demonstrated by its association with grazing or disturbed areas, and its occurrence on sage brush flats with extensive areas of bentonite soils (Knapton et al. 2006). The high-quality breeding habitat within the shrub-steppe communities is a result of poor soil quality, chronically low precipitation, and constant wind scour, which maintains persistent bare patches that are highly stable in space and time (Beauvais and Smith 2003).
Grazing animals also seem to play an important role in maintaining suitable habitat for Mountain Plovers by reducing vegetation cover. In Alberta and Montana, Mountain Plovers have often been found nesting in areas with winter or early spring cattle grazing (Wershler and Wallis 1987; Knowles and Knowles 1998). In Saskatchewan, 4 of 11 Mountain Plover sightings were on black-tailed prairie dog colonies in and around Grasslands National Park (Peart and Woods 1980; Gollop 1987a, 1987b; Wershler 2000; Knapton et al. 2006); in Montana, Mountain Plovers are strongly associated and seem to be at least partly dependent on prairie dogs (Dinsmore et al. 2003; Dinsmore et al. 2005). In Canada, the Richardson’s Ground Squirrel (Spermophilus richardsonii) may also be important in maintaining nesting habitat for Mountain Plovers. While ground squirrels do not change the vegetation height to the extent that prairie dogs do, their burrowing activities could increase the amount of bare ground, potentially improving habitat for Mountain Plovers (Wershler 2000). The report of a pair of Mountain Plovers in Montana nesting in an intensively cattle-grazed grassland site occupied by Richardson’s Ground Squirrels suggests that such habitat will be occupied on occasion (Knowles and Knowles 1998).
2.3.2 Wintering Habitat
The majority of winter records of Mountain Plovers are from the Central and Imperial valleys of California (Knopf and Rupert 1996; Wunder and Knopf 2003), but the plovers also winter in Arizona, Texas, and Mexico (Knopf 1996; Rojas et al 2006). During the winter, Mountain Plovers use cultivated fields, heavily grazed annual grasslands, burned fields (Knopf and Rupert 1995; Wunder and Knopf 2003), coastal prairies, and alkaline flats (Oberholser 1974; Knopf 1996).
Mountain Plovers forage in areas of short (<2 cm) vegetation, including prairie dog towns, heavily grazed pastures, dirt or gravel roadbeds, recently ploughed ground, and fallow fields (Knopf 1996). The diet of Mountain Plovers is almost exclusively invertebrates, including grasshoppers, beetles, crickets, and ants (Baldwin 1971; Graul 1973; Olson 1985; Knopf 1996).
2.4 Existing Protection
As of June 2003, Mountain Plovers were protected under Canada’s Species at Risk Act. In addition, this species is protected under the Migratory Birds Convention Act, 1994; it is also protected in the United States. Legislation prohibits the taking (e.g., hunting or collection) of eggs, nests, or birds in Canada and the United States. Mountain Plovers occurring within the boundaries of Grasslands National Park are also protected under the Canada National Parks Act.
The Mountain Plover has been approved for listing as an endangered species in Alberta (R. Gutsell, pers. comm., 2004). The species is not listed in the Wild Species at Risk Regulations of The Wildlife Act, 1998 of Saskatchewan.
Market hunting prior to the 1900s and the loss of habitat due to cultivation are thought to be the primary reasons for the initial decline of Mountain Plovers in North America. Other threats to the continental population include agricultural practices, management of domestic livestock, decline of native herbivores, and possibly pesticides (COSEWIC 2000). Possible threats to the Canadian population include grassland management, conversion of native grassland to cropland, loss of prairie dogs and possibly ground squirrels, human disturbance, and fluctuations in precipitation (see below). The number of pairs in Canada is (and likely always has been) extremely small and is likely dependent on the abundance and distribution of Mountain Plovers in the United States, particularly in Montana. The persistence of the species in Canada is also dependent on the presence of suitable breeding habitat in Saskatchewan and Alberta.
2.5.1 Grassland Management
Mountain Plover breeding habitat may be threatened by grassland management practices that fail to maintain the presence of areas of short grass or bare ground. Within grassland ecosystems, heterogeneity was once maintained by variations in weather, irregular fires, and large herds of migrating bison (Bison bison). In the present day, vegetation height and habitat heterogeneity are dictated in large part by cattle grazing intensity. Some range management strategies may tend to promote grazing intensities that result in more homogeneous pastures with moderately tall grasses, features that are contrary to the needs of Mountain Plovers (Wershler 2000).
Seeding areas with exotic grasses threatens Mountain Plovers, because these grasses are typically taller than native species; crested wheatgrass (Agropyron cristatum) is generally unsuitable for Mountain Plovers, even when heavily grazed (Wershler and Wallis 2001). Fire suppression on the prairies has likely had negative impacts on nesting habitat for Mountain Plovers, as they will use recently burned native grassland for nesting (Wallis and Wershler 1981; Knowles and Knowles 1984, 1998; Wershler and Wallis 1987; Knopf 1996; Alberta Sustainable Resource Development 2003).
2.5.2 Conversion of native grassland to cropland
The conversion of native grasslands to cropland was prevalent throughout the prairies during much of the last century (Wershler 2000). More than two-thirds of the mixed prairie grassland in Canada was destroyed by cultivation or other development (Wallis 1987), and it is likely that some Mountain Plover breeding habitat was lost. Although cultivation of native grasslands has slowed significantly in southeastern Alberta and southwestern Saskatchewan, habitat alteration within the Canadian range of the Mountain Plover may be a threat to the species (Wershler 2000). In addition to the direct loss of habitat that occurs from cultivating native grass, crop fields can attract Mountain Plovers and may act as reproductive sinks (USFWS 1999). Currently, Canada has sufficient suitable habitat to support the number of Mountain Plovers that can reasonably be expected to occur here annually (2–3 pairs).
2.5.3 Loss of Prairie Dogs
Mountain Plovers are strongly associated with prairie dog towns in several areas of the United States (Knowles et al. 1982; Knowles and Knowles 1984). Black-tailed prairie dogs create and maintain habitat suitable for Mountain Plover breeding by reducing the height and cover of vegetation. In the United States, the distribution and abundance of prairie dogs have been greatly reduced, and they continue to be threatened by sylvatic plague, conversion of grassland, and extermination programs. In Canada, black-tailed prairie dogs occur only in and near the Frenchman River Valley in southern Saskatchewan. They are considered a species of Special Concern under the federal Species at Risk Act. The population of prairie dogs appears to be stable in Canada, although sylvatic plague is a persistent threat.
2.5.4 Human Disturbance
Human disturbance, including oil and gas exploration and development, road and trail development, and birdwatching, may have negative impacts on Mountain Plovers. Mountain Plovers often feed near roads, which can result in direct mortality through road-kill. In addition, human activities may cause distraction displays by adults, which could potentially harm chicks during brood-rearing by overheating them (Graul 1975; USFWS 1999). The effects of human disturbance on Mountain Plovers are largely unknown, and safe distances for developments away from breeding birds have yet to be determined. Pesticide use could threaten Mountain Plovers by directly poisoning individual birds or by reducing the abundance of important prey species.
2.5.5 Fluctuations in Precipitation
Weather extremes, including fluctuations in precipitation, can dramatically change the suitability of Mountain Plover nesting habitat. For example, above-average precipitation can lead to tall, thick grass cover and subsequent unsuitable breeding habitat (Wershler and Wallis 1987). Alternatively, drought conditions may cause birds to leave the breeding grounds early (Leachman and Osmundson 1990) or may result in lower fledging rates by altering food supply and predation pressure (Knopf and Rupert 1996).
2.5.6 Threats to wintering habitat
Wintering areas in California are under pressure from conversion of cultivated fields to vineyards, orchards, and urban development, the loss of grasslands, and potentially environmental contaminants (Leachman and Osmundson 1990; Knopf 1996; Knopf and Rupert 1995). Changes in management practices in the Imperial Valley, such as reductions in the area of coverage of alfalfa, a reduction in domestic grazing, or a reduction in burning following harvest may also reduce habitat available for wintering Mountain Plovers (Wunder and Knopf 2003).
2.6 Knowledge Gaps
There are significant knowledge gaps in every aspect of Mountain Plover biology in Canada. Information is needed on:
· number and distribution of Mountain Plovers in Canada;
· habitat requirements;
· availability of habitat in Canada;
· factors limiting the breeding range in Canada;
· connectivity between U.S. and Canadian populations, and its significance;
· population dynamics at the periphery of the species’ range; and
· effects of human disturbance (e.g., oil and gas development).
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