A spatial model for the beneficial use of dredge spoil deposition: Creation and management of breeding habitat for reddish egrets in Texas

Abstract

Many species of coastal waterbirds have faced population declines in recent years as a result of loss and degradation of habitat. The creation of new habitat through strategic placement of dredge spoil can be an effective tool to mitigate habitat loss. The use of dredge spoil islands for nesting, wintering, and migratory stopover habitat by waterbirds has been documented extensively over the past several decades. Most of the reddish egret (Egretta rufescens) breeding population in the United States occurs in Texas, where it has declined by more than 30% since the 1970s. Reddish egrets breed on dredge spoil islands along the Texas coast, and the stability of breeding colonies has been variable since the 1970s. If nesting habitat is degraded or limiting in Texas, the creation of new nesting islands through strategic dredge spoil placement could benefit reddish egrets. We developed a spatially explicit prioritization model for targeted conservation of reddish egrets in the Laguna Madre, Texas, through colonial island establishment using dredge spoil. Prioritization is based on availability of foraging areas, potential competition at foraging areas, and distance of potential sites to the mainland. ‘Priority areas’ are potential nesting island locations that would maximize the foraging benefits for breeding reddish egrets. Model outputs show that highest priority areas in the Laguna Madre are located in the southernmost portion of the lagoon. Other priority areas are located in the lower Laguna Madre, and at the mouth of Baffin Bay. In addition, we provide a repeatable and transparent framework for the development of spatial support tools that help guide targeted placement of dredge spoil in an effort to conserve colonial waterbirds. We illustrate the model development for reddish egrets, a threatened species in Texas, however our framework can be applied to other similar species.