New York Natural Heritage Program
Pied-billed Grebe
Podilymbus podiceps (Linnaeus, 1758)
Birds

Threats [-]
Currently, the greatest threat to this species is the ongoing alteration and loss of wetlands through draining, dredging, filling, pollution, invasive species and siltation from agricultural practices and roads. These threats lead to the degradation, isolation, and fragmentation of wetlands and have left many marshes that were too small, or were not part of larger marsh complexes, unsuitable for grebes and other marshbirds (New York State Department of Environmental Conservation 2006). Pollution and environmental contamination degrades the food web of wetland ecosystems and can impair the reproductive capacity of pied-billed grebes through the process of biomagnification. Popular organophosphate pesticides used heavily for agriculture have been directly implicated in the death of this species and elevated mercury levels have been detected in some individuals (Gibbs and Melvin 1992). Siltation and runoff from development and agriculture may also negatively impact populations of important prey species. Water level management on Lake Ontario and other large water bodies can alter marsh habitat and decrease the quality of historically utilized sites. In other cases, lack of stochastic events that produce a flushing effect may negatively impact marshbirds by promoting large monotypic stands of emergent vegetation. Invasive aquatic plants such as purple loosestrife crowd out native emergents and form stands too dense, and lacking sufficient open water interspersion, for some marshbird species including pied-billed grebes. Small, localized breeding populations are extremely vulnerable to stochastic events, such as storms, habitat loss, or human disturbance. (New York State Department of Environmental Conservation 2006). Grebes are sometimes mistaken for ducks by hunters and are accidentally shot. Television and cell towers pose an extreme danger to nocturnally migrating individuals, for example 65 pied-billed grebes died at a television tower in Florida between 1955 to 1980 (Muller and Storer 1999).

Conservation Strategies and Management Practices [-]
Restoration of wetland habitat, improvement of water level control at managed wetlands, promotion of the Farm Bill Landowner Incentive Program to manage and restore appropriate habitat, reducing the spread of invasive exotic species, and controlling invasive species where they occur at sites occupied by grebes and other rare marshbirds, are all identified as important management actions beneficial to pied-billed grebes (New York State Department of Environmental Conservation 2006). Because pied-billed grebes will readily colonize wetland impoundments managed primarily for waterfowl, there is ample opportunity to make minor alterations to existing management schemes to improve nesting and foraging habitat for grebes. Since other secretive, rare marshbird species such as American bitterns, least bitterns, and black terns share habitat preferences with pied-billed grebes, management strategies could benefit multiple species of management concern. The conservation of relatively large (5-75 ha) wetlands with roughly a 50/50 interspersion of moderately shallow emergent vegetation and open water (the "hemi-marsh") is the most urgent management need for pied-billed grebes and other marsh-nesting birds. Dense stands of vegetation therefore need to be periodically opened up to retard succession. Properly managed muskrat populations often fulfill this role, but the process may need to be augmented by cutting, burning or flooding. Herbicide treatments are not recommended. Manipulation of water levels provides a cost-effective method for establishing moderately dense stands of emergent vegetation while retaining open water areas preferred by grebes. However, water levels need to be maintained at a stable level during the nesting season to prevent flooding of nests and predator access. Complete drawdown should be avoided so as not to destroy major fish and odonate food items. The floating nests of grebes are easily washed over and capsized by wave action, so large motorized boats should be excluded from occupied marshes, and nesting areas should be protected from heavy recreational use to prevent disturbance of incubating birds (Gibbs and Melvin 1992). In general, pied-billed grebe's high reproductive potential (large clutch size, ability to re-nest following nest loss), in addition to its tolerance of a wide range of freshwater marsh habitats, suggests that management potential is high.

Research Needs [-]
A number of research needs have been identified including: 1) Evaluation of habitat characteristics at multiple scales to better understand micro and macro habitat features important for nest site selection; 2) Conducting controlled experiments to see which management actions are effective locally in producing suitable habitat; 3) Conduct demographic studies at selected sites to identify source and sink populations; 4) Determine major migration stop-over sites and conduct studies of habitat use, prey availability, and diet at migratory staging and molting areas, as well as wintering grounds, to asses possible threats and limiting factors, 5) Investigate aspects of behavioral ecology, such as mate selection, mate fidelity, spacing behavior, coloniality, dispersal, and post fledging parental care; 6) Periodically monitor the levels of contaminants in birds and eggs to assess trends and determine effects on eggshell thinning, behavioral modification, chick development, nesting success, and juvenile survival; 7) Refinement of standardized survey techniques and implementation of programs to monitor population trends; 8) Conduct studies of the structural composition of wetland vegetation, water levels and quality, and wetland area and occupancy relationships during nesting and migration; 9) Evaluate the effects of invasion of non-native invasive marsh plants on grebe habitat suitability (Gibbs and Melvin 1992, New York State Department of Environmental Conservation 2006) .