Restoration Potential: The relatively low reproductive output appears to be due, at least in part, to storms, wind, and waves which destroy nests. Without a better understanding of other causes of low reproductive success which may include contaminant accumulation, predation and human disturbance, and factors affecting the tern away from the breeding grounds, it is difficult to speculate on the likelihood that this species will recover from the widespread population decline it is currently experiencing. However, there are several reasons to believe that if prompt actions are taken, some degree of recovery is possible (Novak 1992).
Renesting after initial nest failure has been reported by various authors (Bergman et al. 1970, Bailey 1977, Novak 1990) and may partially offset losses suffered during initial nest failures. Nesting area choice may vary from one year to the next depending upon changing water levels, nest substrate availability, and vegetation density (Weller and Spatcher 1965, Bailey 1977, Dunn 1979). Because of this sensitivity to habitat change, the tern is not tied to traditional nesting areas if the habitat deteriorates, and may colonize newly created, suitable habitat. For example, in Nova Scotia, terns nested for the first time in the 1970s in new water impoundments (Gerson 1987). The tern can use a variety of nest substrates and is not restricted to wetlands with specific vegetation types. This adaptability reduces the chances of habitat limitation from the lack of available nest sites. Nest success was as high as 50% in one recent study (Firstencel 1987). Although such high nesting success seems to be the exception, it indicates that the tern is capable of achieving high reproductive output under some conditions. Based on banding records, terns may live as long as eight years (Clapp et al. 1982), perhaps longer, and therefore could benefit greatly from several successive years with high reproductive success.
The North American Waterfowl Plan, No-Net-Loss of Wetlands policy, and the "Swampbuster" provision of the Food Security Act of 1985 (P.L. 99-198, commonly known as the 1985 Farm Bill) which prevents farmers who drain wetlands from receiving agricultural subsidies and other economic benefits of the bill, can all help to curtail the destruction of wetlands, essential habitat for terns.
Despite the fact that the tern is currently experiencing a widespread population decline, it has a North American breeding distribution which extends nearly continent-wide. The tern remains widespread and fairly common in much of the Prairie province region and parts of the northcentral and western United States (Gerson 1987, Hands et al. 1989). The tern has actually increased in New Brunswick and began nesting in Nova Scotia in the 1970s (Gerson 1987). The current distribution and population ensures that in most regions, at least for the near future, terns should be able to recolonize traditional or restored sites and colonize newly created habitats.
Relative to overall state populations, large numbers of black terns breed on government managed wetlands in Wisconsin (Mossman 1982), Michigan (Adams 1988, Einsweiler 1988), New York (Novak 1990), Vermont (Laughlin and Kibbe 1985), Maine (Pierson 1983, Gibbs and Melvin 1989), Minnesota (Eliason 1989, Faber 1990, Dulin 1990) and perhaps other states as well. Management of wetland complexes has been employed successfully with waterfowl for many years (Fredrickson and Taylor 1982). Management of wetlands to benefit terns should be possible in many cases and may be largely compatible with practices currently focusing on waterfowl. If human disturbance is determined to have adverse effects on nesting terns, education and restrictions on human access may be employed to eliminate or reduce impact. The ability of terns to use artificial nesting platforms may facilitate restoration efforts (Novak 1992).
Preserve Selection and Design Considerations: Habitat preservation alone will probably not ensure the recovery of the tern in regions where population declines have been substantial (Novak 1992). Successional processes, changes in water levels, invasion by exotic wetland plants, and degradation of water quality, which may alter both the food web and the vegetative structure of the wetland, have the potential to render wetlands unsuitable for use. Management of wetlands will be required to maximize their value to terns. The hemi-marsh stage (Weller and Frederickson 1973), where open water and emergent vegetation are present in approximately equal amounts, is widely recognized as preferred nesting habitat. Development of agricultural lands surrounding wetlands supporting terns should be discouraged because the terns may use the fields for foraging. Maintenance of buffer zones to block siltation, pesticide, and fertilizer runoff to the wetlands may also be desirable. In Iowa, nested mainly in marshes larger than 20 ha; used smaller marshes (5-10.9 ha) only when they were part of a larger wetland complex (Brown and Dinsmore 1986).
Management Requirements: The range of options available for the management of specific sites to benefit terns will vary with the degree to which water levels can be regulated at the site, the size and nature of the site, and the degree to which factors such as predation and disturbance are a problem at the site (Novak 1992). Potential management procedures for a sample of sites of different types are as follows. Changing the water level in marshes can greatly affect use of the marsh; hence the species responds to water management.
In managed inland marsh complexes managers usually have some ability to regulate water levels in various impoundments or pools. Management procedures must vary from site to site depending upon a variety of factors including: size of the area, number of pools in which water levels can be regulated, sources of water for altering water levels, natural precipitation rates, muskrat (ONDATRA ZIBETHICA) populations, and other management goals to be considered. In general, management should be aimed at maintaining one or more large impoundments in the hemi-marsh stage for as long as possible. To avoid flooding of nests, water levels in impoundments should be stabilized from May to July (Novak 1992). Pools in other stages of marsh succession may be used for foraging, but will be less preferred for nesting. Periodic draw-downs and re-flooding, and management of the muskrat population through regulated trapping will be the primary management tools at these sites.
At most natural areas of shallow marsh associated with large lakes, ponds, and rivers there will be no practical means of regulating water levels. Where terns nest in patches of rushes, cattail, or other emergent vegetation (Goodwin 1960, Bailey 1977), maintenance of these "islands" of emergent vegetation is recommended. Because these sites are associated with larger, more open bodies of water, they may be used extensively for boating, fishing, and other forms of water-based recreation. Repeated disturbance and wave action may pose serious threats to reproductive success at these sites. Educational efforts and/or restricting access may be effective at some sites. The degree and type of disturbance may influence the best strategy to be utilized. At colonies with excessive disturbance close to nest sites, restricting entry during the breeding season may be the only option available. In other cases, establishing no wake zones or posting signs to discourage visitors may be effective. However, signs may also draw attention to colony sites and may be ineffective when enforcement is not possible (Connell and Norman 1989). In these situations, efforts to educate the public may be the most reasonable method of reducing disturbance. Placement of artificial nest platforms to encourage terns to nest in areas where disturbance is less of a problem, may provide a further management tool in some instances (Muller et al. 1992). Terns used five of ten artificial nest platforms at one study site in Minnesota (Hands et al. 1989) and nearly 100% of the platforms placed at a managed area in Michigan in 1990 (Scharf, pers. comm.). Although the value of artificial nesting platforms has not yet been demonstrated, they may provide a safer, more stable substrate than naturally floating objects, may be useful in luring terns to nest in more protected locations, and may provide suitable nest substrates in wetlands where natural substrates are in short supply. In any of the above situations, the result may be higher reproductive success. One piece of anecdotal evidence of potential platform benefits comes from a 1990 study in Minnesota (Faber 1990) where eight out of nine nesting attempts on platforms successfully hatched at least one young. In contrast, only 36 of 69 natural nests were successful. However, it is also possible that in some cases platforms may simply lure terns to nest in unproductive sites.
It is possible that extensive predation may pose a serious threat to nesting success at some colonies. Decisions regarding predator management should be made only after identification of specific predators involved, documentation of the extent and effect of the predation, and careful consideration of alternatives and the likelihood of success in ameliorating the situation.
There is a need to incorporate management planning in overall plans for all managed wetlands with suitable tern habitat within the current or historical breeding range in the northeastern and northcentral United States.
Management Research Needs: The list of research and management needs is extensive (Novak 1992). No priority is intended by the order of these needs.
1. Determine the causes of nest failure and mortality in all age classes at nesting colonies in the northeastern and northcentral United States.
2. Evaluate the effectiveness of artificial nest platforms for increasing nesting success or population densities. Emphasis should be placed on sites where natural nest substrates appear to be limited or where terns may be encouraged to nest in areas where disturbance may be reduced.
3. Determine nest site fidelity of adults and philopatry of young.
4. Determine the effects of contaminants on nesting success, chick development, and juvenile and adult survival. Assuming significant negative effects are identified, determine how widespread the effects are across the range.
5. Assess the effects of human disturbance. In the northeastern United States, emphasis should be placed on the impact of boating and other water based recreational activities on nesting colonies.
6. Assess the factors affecting renesting after initial nest failure and determine the productivity resulting from renesting attempts in comparison to initial attempts.
7. Determine foraging range and habitat use at important breeding sites in the northeastern and northcentral United States.
8. Develop or improve the capability to regulate water levels and manage habitat for the benefit of breeding terns at key wetlands in the northeastern and northcentral United States.
9. Determine the movements, mortality rates, causes of mortality, and feeding habits of adults and subadults during the nonbreeding season. Identify migration routes and critical habitats along migration pathways which may be in need of protection. Determine the extent of the winter range. Identify critical overwintering sites and determine faithfulness to these sites.