Status of the Interior Least Tern and Piping Plover in Nebraska

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at 11 sandpits in 1984 when riverine habitat was unavailable because of high water levels. Additional measurements of colony spatial characteristics during years of contrasting flow conditions would facilitate further evaluation of I this matter. Certain parameters such as area per colony, nest elevation above water level, and nest -to -water distances are subject to change during the breeding season with fluctuations in river stage. All of these parameters vary inversely with river stage and, in general, decreasing stage conditions are more favorable to tern and plover colonies. Increases in'area per colony resulting from stage decreases tend to reduce the potential for predation, whereas associated increases in nest elevation and nest -to -water distances reduce potential disturbances from wave action or subsequent rises in water levels (Schwalbach et al. 1986). Stage increases cause reverse effects and, in the event of large increases, complete inundation of nesting areas can occur. Although several researchers (Ducey 1981b, Faanes 1983) have reported that piping plovers tend to nest closer to the water surface elevation than least terns at sandbar colonies along the Platte River, marked differences in nest elevation between species were not apparent at Missouri River colonies in 1986. PRODUCTION Production data for least tern breeding populations in Nebraska indicate considerable variability from year to year and from location to location. Along the Platte River, production rates reported at sandpit colonies in 1984 and 1986 (0.42 and 0.38 fledglings /nesting pair, respectively) were twice as high as reported at river sandbar colonies in 1986 (0.19 fledglings /nesting pair). Moreover, of four Platte River sandbar and two sandpit colonies monitored in 1982 (Ducey 1982), highest production occurred at a sandpit where the owner took an active interest in protecting the nesting birds. The 30 adult terns (15 breeding pairs) observed at this site produced a minimum of 10 fledglings, reflecting a minimum fledging rate /nesting pair of 0.67. Within the Gavins Point Dam to Ponca reach of the Missouri River, fledging rates /nesting pair ranged from 0.60 to 0.16 over the 3 years of record (1982, 1983, and 1986), indicating nearly a four -fold difference between the highest and lowest production years (1982 versus 1986). For the Missouri River reach between Fort Randall Dam and Lewis and Clark Lake, production results in 1986 reflected a fledging rate /nesting pair of 0.50. Production rates have not been determined for breeding populations along the Niobrara or Loup rivers. The low production rates reported at Platte River sandbar colonies and at nesting sites along the Gavins Point Dam to Ponca reach of the Missouri River in 1986 were affected primarily by flooding conditions that occurred after nest establishment. Along the Platte River, flooding was the most frequent known cause of direct loss of eggs during the 1986 breeding season, and losses of chicks to flooding were either observed or highly suspected at most sandbar colonies that year (NGPC 1986). Similarly, all Missouri River colonies showed signs of water disturbance (flooding or wave action) at some time during the 1986 nesting season; nest scrape dampness was also evident at most sites and may have contributed to low production (Schwalbach et al. 1986). The overall rate of production necessary to achieve growth in the interior least tern population is uncertain. However, in light of the species' v