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fledged below Gavins Point Dam in 1983, whereas fledging rates /nesting pair <br />were 0.05 and 0.20 below Gavins Point Dam and Fort Randall Dam, respectively, <br />in 1986. <br />Flooding resulting from high flows subsequent to the next initiation period <br />appeared to be the main cause of low production at piping plover colonies <br />located on sandbars along the Platte River in 1986 and along the Missouri River <br />�- in 1983 and 1986. The higher production rate of 1.8 fledglings /nesting pair <br />determined at sandpit colonies adjacent to the Platte River in 1984 compares <br />favorably with rates reported for colonies along the Atlantic Coast: at one <br />area in Nova Scotia, piping plovers nesting on an isolated, rarely visited <br />beach fledged 1.3 to 2.1 young per pair, whereas birds nesting on a <br />recreational beach at another site fledged 0.7 to 1.1 young per pair (Cairns <br />1977, 1982). The reason for the lower production rates at sandpit colonies <br />along the Platte River in 1986 versus 1984 is not known. <br />Because piping plovers occupy the same types of nesting habitat as least terns <br />(low river bars, beaches, and other exposed land surfaces), they, too, are <br />subject to high temporal and spatial variability in production rates, as <br />influenced by the occurrence of floods, storms, and other disturbance factors. <br />Like least terns, piping plovers are advantaged by a long life span: one <br />banded bird lived to be 14 years old (Wilcox 1962) and, in general, adult males <br />and females may live as long as 10 and 11 years, respectively (Dinsmore 1984). <br />As a result, the species is able to cope with periodic bouts of low <br />productivity. However, the population as a whole cannot be sustained or <br />augmented, unless occurrences of reproductive failure are balanced or augmented <br />by occurrences of reproductive success. <br />{ As has been noted by the Nebraska Game and Parks Commission (NGPC 1984 and <br />1986) production rates reported for least tern and piping plover breeding <br />�_. populations should be viewed with caution because 1) the mobility and dispersal <br />of young birds from their nests soon after hatching makes it difficult to <br />monitor development through to fledging (age at first flight); and 2) lack of <br />nesting synchrony among and between colonies results in young reaching fledging <br />age at different times. Based on similar observations during studies of least <br />tern colonies along the Texas coast, Thompson and Slack (1984) determined that <br />single counts of fledglings substantially underestimate cumulative production <br />among colonies. Instead, they concluded that multiple counts timed with the <br />breeding chronology for colonies within the survey area, and corrected for <br />juvenile departure, are required to achieve more realistic estimates of <br />survival to fledging. They stated that empirical verification at other nesting <br />areas was warranted. <br />To more effectively monitor the health and status of least tern and piping <br />plover populations in Nebraska (and elsewhere within the species, breeding <br />ranges), priority should be placed on the collection of accurate production <br />data in accordance with the procedures recommended by Thompson and Slack <br />(1984), and in consort with regular censusing and management initiatives. <br />FACTORS AFFECTING PRE - FLEDGLING MORTALITY <br />Available data and observations recorded during systematic surveys indicate <br />that main sources of pre - fledgling mortality at least tern and piping plover <br />colonies along Nebraska rivers include flooding, human disturbance, and <br />vii <br />