Are Waterfowl Food Resources Limited during Spring Migration? A Bioenergetic Assessment of Playas in Nebraska\u2019s Rainwater Basin

Travis J Schepker,Elisabeth B Webb,Ted Lagrange

doi:10.1007/s13157-018-1047-0

Abstract

Accurate bioenergetic carrying capacity estimates of wetlands on public and private lands, as well as those managed for crop production are important for managing waterfowl populations and habitats. Given the importance of wetlands in the Rainwater Basin region of Nebraska for spring migrating waterfowl, we quantified and compared seed and aquatic invertebrate biomass and true metabolizable energy (TME) at three wetland types; public wetlands, wetlands enrolled in the Wetlands Reserve Program (WRP), and cropped wetlands. Median seed biomass estimates at public, WRP, and cropped wetlands were 593 kg/ha, 561 kg/ha, and 419 kg/ha respectively. Cumulative TME varied among wetland type, with greater TME at cropped wetlands (2431 kcal/kg) than public (1740 kcal/kg) and WRP wetlands (1781 kcal/kg). Seed biomass estimates from this study were statistically greater than those currently used for management planning in the RWB, however, TME estimates were statistically lower than estimates currently assumed for WRP and public wetlands. Our estimates for aquatic invertebrate biomass were approximately 40-fold less than seed biomass estimates. Based on spring ponding frequency at wetlands in Nebraska’s Rainwater Basin, and the caloric estimates derived for each wetland type, we concluded that the regions wetlands meet the energetic demand of spring migrating waterfowl during 10% of years.

Highlights

The spring condition hypothesis acknowledges the potential relationship between food availability at migration stopover sites and subsequent reproductive success on breeding grounds (Afton and Anderson 2001; Anteau and Afton 2009)
Initial seed samples were collected at all sites prior to arrival of most spring migrating waterfowl, regardless of inundation status, and a second time when we considered the majority of spring migrants had departed the region
Overall true metabolizable energy (TME) was greater in cropped fields than public wetlands, but TME did not differ among other pairwise comparisons (p > 0.05; Fig. 3)

Summary

Introduction

The spring condition hypothesis acknowledges the potential relationship between food availability at migration stopover sites and subsequent reproductive success on breeding grounds (Afton and Anderson 2001; Anteau and Afton 2009). Wetlands (2019) 39:173–184 managers have adopted a bioenergetics approach to guide habitat conservation planning for remaining wetlands at spring staging areas (North American Waterfowl Management Plan 2012; Straub et al 2012; Rainwater Basin Joint Venture (RWBJV) 2013; Williams et al 2014) This approach requires accurate estimates of: 1) habitat-specific food resource biomass (dry weight/unit area), 2) habitatspecific estimates of true metabolizable energy (TME; kcal/ dry weight), 3) habitat-specific availability (ha of foraging habitat), 4) species-specific daily energy expenditure (kcal), and 5) species-specific population goals (Williams et al 2014). Regional conservation planning using a bioenergetics approach is likely hindered by variation and uncertainty in daily ration model parameters, the need for more accurate habitat-specific estimates of food resource biomass and corresponding TME values (Straub et al 2012; Williams et al 2014; Livolsi et al 2015)

Methods

Results

Conclusion