Status of the Interior Least Tern and Piping Plover in Nebraska

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predation. Periodic high flows impact production at riverine sandbar sites on a frequent basis and appear to be the greatest single factor affecting nesting success. Depending on timing, flood events can impact tern and plover nesting activity in two ways. First, the occurrence of high water levels during the nest selection period causes the reduction of exposed sandbar nesting habitat, to the extent that under extreme and prolonged conditions (as occurred on the Platte River in 1983 and 1984) virtually all riverine sandbars may be inundated throughout the breeding season. Second, the occurrence of high flows after nest establishment can result in substantial mortality (and in some cases complete loss) of eggs and young at sandbar colonies. Flooding is not typically a major source of mortality at off -river sandpits which provide nesting habitat for a significant portion of the Platte River breeding populations. The greater stability of water -level conditions characteristic of these sites appears to be the reason that highest reported production rates to date have occurred at sandpits, as opposed to riverine sandbar sites, along the Platte River. Human activities in the vicinity of tern and plover nesting areas pose a regular threat to nesting success at riverine colonies along the Platte and Missouri rivers, and at off -river sandpits adjacent to the Platte. Such activities likely have a proportionately greater impact on production when favorable water level conditions exist throughout the breeding season. Nesting colonies on the Niobrara River are probably less affected by human disturbances because 1) unlike the Platte and Missouri, this river is relatively far removed from major urban centers; and 2) access to the river channel is limited in areas where tern and plover colonies occur. Sandbars along the Platte and Missouri rivers support a variety of human recreational uses in summer including hiking, picnicking, camping, fishing, sunbathing, driftwood collection, nature exploration and fireworks displays. Among the human activities encountered at sandpits, the use of recreational vehicles is of particular concern. These disturbances may prevent nesting at an otherwise suitable site, or cause abandonment and /or direct mortality of eggs and young after nests have been established. Nest abandonment at least tern colonies can also be caused by factors other than disturbances. Based on extensive observations of the Bell Island colony on the Ohio River, Hardy (1957) reported that adult least terns often deserted remaining eggs once the first hatched chicks left the nest. Predation at tern and plover colonies along Nebraska rivers is affected by a variety of birds, reptiles, and terrestrial mammals; however it is not known whether any one of these groups has a more pronounced impact on nesting mortality than the others. Water surrounding riverine sandbar colonies may �. discourage access by terrestrial predators to some extent, but it does not deter predation by avian species or most reptiles (snakes and turtles). Although it has been suggested that greater losses from predation may occur at off -river sandpits, recent monitoring of colonies along the Platte River has not revealed major differences in predation- caused mortality, or the kinds of predators present, at sandpit versus riverine sandbar colonies. In this regard, Hardy (1957) noted that many successful least tern colonies have been reported at locations that are not completely surrounded by water barriers. Similarly, piping plovers in the northern prairie region are known to often nest along the shores of alkali lakes (Ryan and Prindiville 1984) at sites that viii