Threats to Wildlife and the Platte River

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WELDLIFE p. 23 the Platte, hatching occurs from June to July, and young begin flying by the time they are three weeks old. The young continue to be fed by their parents for some time after hatching while they develop fishing skills. In 1987, 604 Least Terns and 206 Piping Plovers were found at 61 nesting sites from Grand Island to Plattsmouth in and along the Platte River (Dinan 1987). These numbers are the highest ever recorded for the river, but it is unclear to what extent these represent population increases rather than better surveys. It is interesting to note that 52 percent of the nesting sites in this survey had no history of prior use. This suggests their populations have been increasing, however, high colony -site turnover is common in Least Terns, especially if disturbance is prevalent (Kotliar and Burger 1986). Preferred nesting habitat consists of unvegetated or sparsely vegetated (up to 30 percent herbaceous groundcover, less than one foot in height), dry sandbars (E. Kirsch 1988, pers. comm.) Roughly two - thirds of the new nesting sites found in the 1987 Nebraska Game and Parks Com- mission survey were on sandbars; the rest were on sandpits associated with gravel and sand mining operations. Eighty -six percent of all sandbar sites used were downstream from the confluence of the Loup River. Since these surveys began in 1981, 48 river sandbar and 37 sandpit nesting sites have been used by terns and plovers. Seventy percent of all Least Tern nests during this time period occurred downstream of the confluence of the Loup River. Eighty percent of the terns that were surveyed downstream of the Loup's mouth used sandbar sites. This pattern of nesting habitat selection suggests a preference for midstream sandbars. Further, a higher percentage of the available sandbars are used than of the available sandpits (E. Kirsch 1988, pers. comm.). Sandbars in mid- stream help to protect the nesting birds from predators and human disturbance by providing a water barrier (NGPC 1985a, p 43).9 Of the colonies surveyed for Least Tern fledglings by the Nebraska Game and Parks Commission in 1987, more sandbars were used and sandbars were more productive than sandpits (at least in 1987). Consequently, sandbars appear to be more important to the population than 9 Human disturbance, especially by "all- terrain" vehicles, has been a problem for these birds in both types of breeding habitat. River flows above 800 cfs largely prevent access and disturbance by all- terrain vehicles to river sandbar colonies (USFWS 1987b, pp 34 -35). It seems reasonable to suppose that if human disturbance is a factor, and sufficient flows to produce good water bar- riers are provided, sandbar productivity will be consistently higher than in spoil areas.