Reproductive ecology of interior least tern and piping plover in relation to Platte River hydrology and sandbar dynamics.

Jason M Farnsworth,Kevin L Werbylo,Chadwin B Smith,David M Baasch

doi:10.1002/ece3.2964

Abstract

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.

Highlights

Interior least tern (Sternula antillarum athalassos; hereafter, least tern) and piping plover (Charadrius melodus) (Figure 1) are two species of endangered and threatened birds that nest on barren to sparsely vegetated riverine sandbars, sand and gravel pits, and along lake shorelines in North America (USFWS, 1990)
As hypothesized, least tern and piping plover are physiologically adapted to begin nesting on the Platte River concurrent with the recession of the spring rise, we would expect this to be reflected in the timing of species nest initiation
This adaptation is apparent in analyses of least tern nesting data on the lower Mississippi River where the annual hydrograph peaks in April and least tern nest initiation period begins in May, following the peak (Dugger, Ryan, Galat, Renken, & Smith, 2002)

Summary

| INTRODUCTION

Interior least tern (Sternula antillarum athalassos; hereafter, least tern) and piping plover (Charadrius melodus) (Figure 1) are two species of endangered and threatened birds that nest on barren to sparsely vegetated riverine sandbars, sand and gravel pits, and along lake shorelines in North America (USFWS, 1990). The decline in AHR habitat suitability has been inferred from (1) the body of evidence documenting a substantial change in central Platte River (CPR) hydrology and associated reduction in unvegetated channel width over historical timeframes, (2) the presence of species nesting on off-channel habitat, but lack of suitable sandbar nesting habitat and on-channel productivity in the contemporary CPR, and (3) species use of riverine habitat in the contemporary lower Platte River (LPR) which experiences higher peak flow magnitudes. There have been few attempts to quantitatively evaluate differences through comparative analyses In this investigation, we endeavored to (1) examine the timing of the late spring rise in relation to least tern and piping plover nesting ecology on the historical and contemporary CPR and the contemporary LPR and (2) compare and contrast the potential for on-channel species productivity in the CPR and LPR segments given our current understanding of basin hydrology, channel hydraulics, and sandbar height relationships

| METHODS

Findings

| DISCUSSION