Limiting factors are considered to be those conditions that degrade
habitat suitability, reduce survivorship of young or adults, or decrease nesting success of adults once they are established at a site. Although factors such as weather may influence plover populations, the present discussion focuses on conditions that may be linked to human activities on, or near, Piping Plover habitats. Such as
Hydrology and Vegetation Encroachment, Industrial Development,
Livestock Grazing, Human
Disturbance, Predation, and Habitat
Hydrology and Vegetation
Encroachment: The presence of suitable nesting habitat for Piping Plovers requires alternating periods of high and low water that removes vegetation and exposes gravel substrates on nesting beaches. Concern has been expressed that demands on water from agriculture and other industries, coupled with a loss of native vegetation surrounding water bodies, may be altering the normal hydrology of nesting basins in Alberta. Such demands might promote vegetation encroachment by reducing the frequency of
high water events. Concern has also been expressed over projects that stabilize water levels to enhance recreational opportunities. Such projects are underway at Buffalo Lake, and have been proposed for Little Fish Lake. Stabilization of water levels for recreation or irrigation supply may also limit plover habitat on Lake Newell and Keho. The typical practice of raising water levels to fall supply level on reservoirs after birds have started nesting is particularly destructive to plovers.
It has been suggested that the exploration and extraction of fossil fuels around plover breeding sites could pollute water and shorelines, deplete water levels or interfere with ground water dynamics, and eliminate surrounding vegetation. The direct impacts of oil and gas development on plover habitat are not well documented, but activity has been reported in close proximity to at least seven known breeding sites in Alberta. In addition, changes in water chemistry and beach substrates attributed to potassium sulphate development have been observed at several breeding locations in Saskatchewan, and possibly at Horseshoe Lake in Alberta. Despite fears of water contamination by agricultural chemicals or industrial development, chemical analysis of Piping Plover eggs in Alberta has revealed no significant chemical residues. Thus, industrial activities may affect the suitability of shorelines for nesting, but there is no evidence that chemical residues have impacted the breeding performance of Piping Plovers in this region.
Livestock can disturb nesting substrates, interfere with normal nesting behavior by established birds, and directly destroy eggs. In addition, young plovers may fall into deep hoof prints and be unable to escape, and construction of dugouts adjacent to shorelines can foul nesting beaches, change basin hydrology and accelerate vegetative encroachment. Cattle impacts on shorelines generally increase with decreasing salinity. Even though most plover habitat on the Great Plains occurs on alkaline lakes, the impacts of grazing on plovers in this area can be substantial. Livestock activity is one of the major factors limiting breeding production by Piping Plovers in Alberta, but there are a number of effective and inexpensive measures that can be employed to reduce such impacts.
Human disturbance occurs through motorized off-road travel (all-terrain vehicles), or by nonmotorized, recreational use of beaches. Such disturbances may affect plovers by directly destroying nests and eggs, or by interfering with territorial establishment and other reproductive behaviors. Studies on the Atlantic coast have documented decreased nest success on beaches with human disturbance. The authors speculated impacts on fledging success may result from reduced time spent foraging and increased vigilance by chicks in areas with frequent human activity. Most plovers in Alberta nest on lakes that are unattractive for recreation, and human activities are generally restricted to a brief period during the summer. However, most plovers begin nesting in early May, so recreational activities later in the summer would likely disturb active nests or broods.
Predation on eggs and chicks is probably the
greatest source of reproductive
failure in Piping Plovers on the Great Plains. In one instance, 40% of nests in Manitoba were lost to predators. Red Foxes and Striped Skunks, American Crows, and gulls are most often implicated on the Great Plains, but
Black-billed Magpies, Great Homed Owls, Northern Harriers, Coyotes, Raccoons, weasels and domestic dogs have also been observed, or suspected of, preying upon eggs or young. Although the loss of eggs and chicks to predators is a natural process, there is evidence that urbanization and recreational use of beaches have increased populations of gulls, foxes and skunks in some areas. Predation is currently a major cause of reproductive failure in this province, and research directed towards minimizing this impact may lead to simple management tools which can enhance reproductive success of Piping Plovers.
Development of Habitat on the Winter Range:
Piping Plovers spend only one third of their annual cycle on the breeding grounds, so most mortality of adult birds probably occurs on wintering areas or during migration. Events occurring far to the south of Alberta therefore have potential for major impacts on local Piping Plover populations. There has been little quantification of the threats to Piping Plovers on the wintering grounds. However, a number of potential factors have been identified, including oil spills, recreational activities, dredging, and construction of seawalls and jetties that affect normal beach dynamics, expansion of intercoastal waterways, beach restoration, and dune stabilization. The relatively high fidelity of birds to wintering areas suggests that protection of traditional wintering sites from such threats should be an important component of recovery plans for this species.
Reprinted from Alberta Wildlife Status Report No. 1 (1997), with permission
from Alberta Sustainable