Status of the Interior Least Tern and Piping Plover in Nebraska

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i F= vulnerable habit of nesting on low river bars and other land surfaces exposed to the rigors of the plains climate (rainstorms, wind storms, hail, floods, and intense heat), low production is undoubtedly a regular occurrence. As reported by McNicholl (1975), nesting in widely fluctuating habitats requires flexibil- ity in selecting nest sites, but unstable or immediately stable habitat may not prove successful every year. Hardy (1957) commented that sudden rises of water sufficient to inundate tern colonies are particularly likely in streams traversing the plains region, and in many colonies (especially those on low bars) floods take a heavy toll. He further stated that the "extremely high mortality" of young least terns up to the flying stage is compensated by low mortality in adults. For California least terns, Atwood and Massey (1981) indicated that a production rate of 1.0 -1.5 fledglings /nesting pair is considered good success, 0.50 -1.0 /pair is moderate, and 0 -0.5 /pair is poor. For Atlantic Coast least terns, on the other hand, Burger (1984) considered colonies producing more than 0.5 fledglings /nesting pair as successful, and those producing 0.25 -0.49 fledglings /pair as moderately successful. Burger additionally reported that reproductive success for least tern colonies in New Jersey averaged 0.48 fledglings /nesting pair (range: 0.2 to 0.8 fledglings /pair) over the 5 -year period 1978 -1982 during which time the number of breeding birds increased significantly. Ultimately, however, determination of whether a given production rate results in population increase or decrease is dependent on the level of production necessary to maintain a stable or self- sustaining population (where mortality in the breeding stock is balanced by production). Because of more rapid population turnover, short -lived species require higher production rates to maintain their populations. Consequently, the long life span of the least tern (one banded bird lived to be 21 years old [Wingfield 1982]) is of definite survival importance. Based on a 10 -year breeding span for adult least terns (Wingfield 1982), and assuming 33 percent mortality from fledgling stage to reproductive maturity at age 2, the mean annual production rate required to maintain a self - sustaining population would be 0.30 fledglings /nesting pair. Maintenance of a self- sustaining production rate of 0.30 fledglings /nesting pair would, in effect, require that each pair of adult least terns in the population produce three fledglings any time during their 10 -year breeding span. Lower production one year could be offset by higher production the next, or higher production at one nesting area could compensate for lower production at another. Within this context, cumulative production rates above 0.30 fledglings /nesting pair would affect population growth, whereas lower rates would affect population decline. If subsequent information indicates the average number of breeding years per adult is less than or greater than 10, or that juvenile mortality is less than or greater than 33 percent, then a higher or lower production rate would be necessary to achieve a self- sustaining population. Production data for piping plovers, which in Nebraska utilize the same types of nesting habitat as least terns, also reflect considerable variability between years and from one location to the next. Along the Platte River, production rates reported at sandpit colonies in 1984 (1.80 fledglings /nesting pair) were substantially higher than those reported at sandpit or river sandbar colonies in 1986 (0.27 and 0.23 fledglings /nesting pair, respectively). Along the Missouri River, approximately 0.24 piping plover young per nesting pair were vi