Local and Landscape Habitat Associations of Shorebirds in Wetlands of the Sacramento Valley of California

Abstract

The Sacramento Valley of California is a site of international importance for shorebirds despite having lost >90% of its historic wetlands. Currently both managed wetlands and flooded agriculture are important habitats for shorebird populations, but the extent of flooded agriculture may be declining in early winter when shorebirds need to acquire resources postmigration to survive winter. We employed long-term shorebird monitoring data to evaluate factors influencing abundance and species richness of shorebirds using the Sacramento National Wildlife Refuge Complex in early winter (November–December) between 2000 and 2009. We quantified the effect of local attributes of the wetland management unit (wetland type, size, and topography) as well as factors in the surrounding landscape (proportion of surface water and housing density) using generalized linear mixed models. We assessed a local-scale model, including covariates representing the area of six wetland types within the management unit, an index to the proportion of the management unit that had a tapered-edge (i.e., topography where flooded areas grade to exposed shoreline then upland), and a year effect. In this local-scale model, shorebird abundance had a significant positive association with the area of seasonally flooded marsh (SFM) and summer water. Topographical variation, characterized by the amount of tapered-edge, also had a significant positive effect on the abundance of shorebirds and species richness. Because >70% of the shorebirds were counted in SFM, we removed all wetland types except SFM to evaluate landscape covariates. Using only SFM-dominated units, there was a significant nonlinear association with the area of SFM within a management unit, with 40–95-ha wetlands having the highest shorebird abundance and species richness. On a landscape scale, the amount of flooding within a 10-km buffer was the best supported model of shorebird abundance and suggested the highest shorebird abundance in a management unit to be expected when 15–45% of the surrounding landscape was flooded. Species richness was positively associated with the proportion of surface water within 2- and 5-km buffers. We identified zones with a predicted high shorebird response to SFM, and assessed that only 6% of potential wetland areas in those zones have permanent conservation status. Our analyses suggest that shorebird abundance and species richness vary nonlinearly as a function of both local and landscape factors, and thus both spatial scales should be considered when developing conservation and management strategies.

A Bioenergetics Approach to Setting Conservation Objectives for Non-Breeding Shorebirds in California’s Central Valley

“…We also assumed an ideal free distribution (Fretwell and Lucas 1969) of shorebirds across all available habitat throughout the Central Valley and our (Taft et al 2002;Reiter et al 2015b). However, changes in habitat availability during one part of the season can affect energy availability later in the season in unexpected and non-linear ways, such that a 50% increase in available habitat does not necessarily correspond to a 50% decrease in energy shortfalls.…”

“…An extensive network of restored and managed wetlands and post-harvest flooded rice, corn, and other crops currently provide substantial habitat for non-breeding shorebirds in the Central Valley (Fleskes et al 2012;Strum et al 2013;Reiter et al 2015b). However, the timing, extent, and depth of flooding can greatly affect their value as shorebird foraging habitat (CVJV 2006).…”

Tidal marsh restoration stimulates the growth of winter shorebird populations in a temperate estuary

“…The restoration of previously lost or degraded tidal or nontidal wetlands, or the protection of key habitat features in tidal wetlands, have been associated with numerous benefits to wintering shorebirds. These benefits include increases in the extent of suitable foraging areas (Atkinson ; Armitage et al ; Patten & O'Casey ), including seasonally available habitat (Colwell & Dodd ; Warnock & Takekawa ); landscape position and proximity to natural wetlands (Brusati et al ; Reiter et al ); increased food supply or availability (Atkinson ; Miller & de Rivera ); reestablishment of the natural hydroperiod and water levels suitable for foraging (Bellio & Kingsford ; Brand et al ); development of roosting opportunities or other conditions that facilitate improved predator avoidance (Rogers et al ; Huang et al ); and enhancement of alternative feeding opportunities when primary foraging areas are rendered unsuitable by flooding or tidal inundation (Warnock et al ; Armitage et al ; Gomez‐Sapiens et al ).…”

“…Reiter et al () demonstrated the importance of seasonally flooded wetlands within a 10‐km buffer (314 km 2 ) in predicting winter shorebird abundances. Their work was conducted on interior landscapes characterized primarily by seasonally flooded marshes, which may differ substantially from coastal wetlands with regard to spatial scales of variation in shorebird abundances.…”

Population and Habitat Objectives for Breeding Shorebirds in California's Central Valley

“…Small adjustments could be made based on the feasibility of habitat restoration or the distribution of focal species most in need while maintaining viable populations in each planning region. Further, despite the strong dispersal ability of shorebirds, the spatial distribution of habitat within each planning region may also affect habitat use and subsequent achievement of density and population objectives (Reiter et al 2015). We recommend creating and restoring habitat in areas that cluster habitat and maximize connectivity of semi-permanent wetlands and other shorebird breeding habitat.…”