Investigations of breeding ecology of interior least tern (Sternula antillarum athalassos) and piping plover (Charadrius melodus) in the Platte River basin in Nebraska, USA, have embraced the idea that these species are physiologically adapted to begin nesting concurrent with the cessation of spring floods. Low use and productivity on contemporary Platte River sandbars have been attributed to anthropomorphically driven changes in basin hydrology and channel morphology or to unusually late annual runoff events. We examined distributions of least tern and piping plover nest initiation dates in relation to the hydrology of the historical central Platte River (CPR) and contemporary CPR and lower Platte River (LPR). We also developed an emergent sandbar habitat model to evaluate the potential for reproductive success given observed hydrology, stage-discharge relationships, and sandbar height distributions. We found the timing of the late-spring rise to be spatially and temporally consistent, typically occurring in mid-June. However, piping plover nest initiation peaks in May and least tern nest initiation peaks in early June; both of which occur before the late spring rise. In neither case does there appear to be an adaptation to begin nesting concurrent with the cessation of spring floods. As a consequence, there are many years when no successful reproduction is possible because emergent sandbar habitat is inundated after most nests have been initiated, and there is little potential for successful renesting. The frequency of nest inundation, in turn, severely limits the potential for maintenance of stable species subpopulations on Platte River sandbars. Why then did these species expand into and persist in a basin where the hydrology is not ideally suited to their reproductive ecology? We hypothesize the availability and use of alternative off-channel nesting habitats, like sandpits, may allow for the maintenance of stable species subpopulations in the Platte River basin. K E Y W O R D Scentral Platte River, hydrology, interior least tern, lower Platte River, piping plover, reproductive success, sandbar height distributions, stage-discharge relationships
The Flow-Sediment-Mechanical approach is one of two management strategies presented in the Platte River Recovery Implementation Program's (Program) Adaptive Management Plan to create and maintain suitable riverine habitat (≥200 m wide unobstructed channels) for whooping cranes (Grus americana). The Program's Flow-Sediment-Mechanical management strategy consists of sediment augmentation, mechanical vegetation clearing and channel widening, channel consolidation, and short duration high flow releases of 142–227 m3/s for three to five days in two out of three years in order to increase the unvegetated width of the main channel and, by extension, create and maintain suitable habitat for whooping crane use. We examined the influence of a range of hydrologic and physical metrics on total unvegetated channel width (TUCW) and maximum unobstructed channel width (MUOCW) during the period of 2007–2015 and applied those findings to assess the performance of the Flow-Sediment-Mechanical management strategy for creating and maintaining whooping crane roosting habitat. Our investigation highlights uncertainties that are introduced when exploring the relationship between physical process drivers and species habitat metrics. We identified a strong positive relationship between peak flows and TUCW and MUOCW within the Associated Habitat Reach of the central Platte River. However, the peak discharge magnitude and duration needed to create highly favorable whooping crane roosting habitat within our study area are much greater than short duration high flow releases, as currently envisioned. We also found disking in combination with herbicide application to vegetated portions of the channel are effective for creating and maintaining highly favorable unobstructed channel widths for whooping cranes in all but the very driest years. As such, resource managers could prioritize the treatment of mid-channel islands that are vegetated to increase the suitability of roosting habitat for whooping cranes.
ABSTRACT. Given the high productivity of Interior Least Terns (Sternula antillarum athalassos) and Piping Plovers (Charadrius melodus) on constructed off-channel nesting sites along the central Platte River in Nebraska, USA, and the possibility of creating similar habitats at other locations in their breeding range, understanding how these species use off-channel nesting habitats is important. We used data collected along the central Platte River in Nebraska, USA, over a 15-year period (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), and a discrete-choice modeling framework to assess the effects of physical site attributes and inter-and intraspecific associations on off-channel nest-site selection by Interior Least Terns and Piping Plovers. We found that Piping Plovers avoided nesting near each other, whereas colonial Interior Least Terns selected nest sites near those of conspecifics. In addition, the relative probability of use for both species was maximized when distance to the nearest predator perch was ≥ 150 m and elevation above the waterline was ≥ 3 m. Probability of use for nesting by Interior Least Terns increased as distance to water increased, whereas the probability of use by Piping Plovers was maximized when distance to water was~50 m. Our results suggest that important features of constructed, off-channel nesting sites for both species should include no potential predator perches within 150 m of nesting habitat and nesting areas at least 3 m above the waterline. Efficient site designs for Interior Least Terns would be circular, maximizing the area of nesting habitat away from the shoreline, whereas an effective site design for Piping Plovers would be more linear, maximizing the area of nesting habitat near the waterline. An efficient site design for both species would be lobate, incorporating centralized nesting habitat for Interior Least Terns and increased access to foraging areas for nesting and brood-rearing Piping Plovers. RESUMEN.Selecci on de sitio de anidaci on por Sternula antillarum y Charadrius melodus en localidades con manejo y fuera del canal a lo largo del tramo central del rio Platte en Nebraska, USA Dada la alta productividad de Sternula antillarum y Charadrius melodus en sitios de anidaci on construidos fuera del canal a lo largo del tramo central del r ıo Platte en Nebraska, USA y la posibilidad de crear h abitats similares en otras localidades en sus rangos de reproducci on, es importante comprender como estas especies usan estos h abitats de anidaci on fuera del canal. Utilizamos informaci on colectada a lo largo del tramo central del r ıo Platte en Nebraska, USA, a lo largo de un periodo de 15 años (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015) y un marco de modelamiento por selecci on discreta para determinar el efecto de los atributos f ısicos y asociaciones inter e intra-espec ıficas en la selecci on de sitios de anidaci on fuera del canal por Sternula antillarum y Charadrius melodus. Enc...
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