Status of the Interior Least Tern and Piping Plover in Nebraska

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versus 1975 is in clear contrast to Downing's (1980) prediction that, without active habitat protection and enhancement, "[a]lmost complete loss of these populations may occur in a few years." Since the initiation of systematic surveys along Nebraska rivers, the discernible trend during years of similar survey coverage and effort has been one of increasing rather than decreasing populations. These increases may reflect 1) the improved ability of investigators to locate nesting colonies (resulting from greater experience and knowledge of the species' behavior and nesting habits); 2) distributional shifts, or immigration of adult birds from other nesting areas within the breeding range; 3) true population increases; or 4) a combination of all factors. Regardless of which factors apply, recent survey results attest to the fact that habitat along these rivers can support considerably larger least tern breeding populations than was previously thought to be the case. More recently, systematic surveys along the Platte, Missouri, and Niobrara rivers have been expanded to include the collection of more complete census data on piping plovers. However, because expanded survey emphasis was not initiated concurrently among all rivers, insufficient data presently exists to evaluate trends in the statewide population over time. Nonetheless, as in the case of the interior least tern, results clearly indicate that Nebraska's piping plover population is substantially larger than earlier believed, and that the state is an important stronghold for this species as well. In 1986, the following numbers of adult piping plovers were censused along various rivers in the state: 164 along the Platte; 172 along the Missouri below Gavins Point Dam; and 11 along the Missouri below Fort Randall Dam. Although the Niobrara River was not surveyed in 1986, 100 birds -were censused along this river in 1985. Assuming stable abundance along the Niobrara from 1985 to 1986, these census results reflect a total statewide population of approximately 450 adult piping plovers as of the 1986 breeding season. Since recent systematic surveys have not inventoried all potential or known nesting habitat within the state, this estimate should be considered conservative. By way of comparison, the statewide population of approximately 450 piping plovers, as determined from systematic surveys through 1986, is about nine times larger than estimated in 1983 (Haig 1985) before comprehensive census information was available for major breeding areas in the state. Based on a review of the species' status reported by Haig (1985), the present breeding population in Nebraska exceeds that of all other states in the nation, and is second only to Saskatchewan among the Canadian provinces. SHIFTS IN COLONY LOCATIONS Interior least terns and piping plovers exhibit an opportunistic nest site selection strategy that provides resiliency in responding to temporal and spatial changes in the availability of suitable habitat. Systematic surveys along Nebraska rivers provide clear documentation that both species make frequent changes in nesting colony locations. By nature, riverine sandbars are ephemeral and go through natural successional cycles of formation, shifting and /or stabilization, and vegetation development. In addition, water -level fluctuation, as affected by the high variability in runoff and precipitation characteristic of the region, may reduce or enhance the availability of riverine or interior wetland habitat either broadly or locally from one year to iii