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<br />Pooulation BiololZV: The interior least tern's annual reproductive <br />success varies greatly along a given river or shoreline (Table 6). <br />Because tern's use ephemeral habitats ,they are susceptible to frequent <br />nest and chick loss. Consequently there are great local differences in <br />productivity. In 1987, total number of interior least terns reached 4,800 <br />(Table 7). This is considerably higher than the 1,200 interior least <br />terns estimated by a partial survey in 1975 by Downing (1980). There are <br />no comprehensive historic numbers to compare with these figures, although <br />early qualitative descriptions indicate that the interior least tern was <br />rather common (Burroughs 1961, Hardy 1957). Increased censusing efforts <br />during the past few years probably account for the differences among <br />recent census figures and earlier surveys. <br /> <br />Table 6. Some examples of the productivity of interior least terns. <br /> Nest Fledgings Frequency % Population <br />Locations Year Success oer Pair of Visits Monitored Source <br />Missouri 1988 0.62 0.42 7-10 days 100% Mayer and <br />River 1989 0.56 0.21 " " Dryer 1989 <br />North Dakota <br />Missouri 1986 0.20 7-10 days 100% Schwalbach <br />River 1987 0.64 " " 1988 <br />South Dakota <br />Missouri 1988 0.36 0.44 7-10 days 100% Dirks 1990 <br />River 1989 0.51 0.55 " " <br />South Dakota <br />Lower 1987 0.57 0.29 2-3 days 39% Kirsch 1987-89 <br />Platte River 1988 0.67 0.71 " 44% <br />River 1989 0.43 0.47 " 42% <br />Nebraska <br />Cimarron 1982-83 0.18 1.09-0.56 Schulenberg <br />River and Ptacek <br />Kansas 1984 <br />Salt Plains 1987 0.44- 0.44- 1-3 days Hill 1987 <br />NWR, Oklahoma 0.33 0.15 <br /> <br />13 <br />