Harte Research Institute at Texas A&M University Corpus Christi, Caesar Kleberg Wildlife Research Institute at Texas A&M University Kingsville, and Coastal Bend Bays & Estuaries Program

The NOAA-funded Colony Island Network Design and Implementation Project leverages information collected from a pilot study conducted between 2021 and 2023. On this page, you will find information and results from the pilot study.

Background

Colonial-nesting waterbirds, including wading birds, gulls, terns, and pelicans, concentrate annually to breed on small coastal islands. Over $24 million has been invested in colony island projects along the Gulf Coast to address threats facing existing nesting habitats and current island creation and rehabilitation projects often rely on educated guesses regarding potential bird populations and are decided by engineering feasibility and available funding rather than strategic planning.

There is a clear need for a prioritization tool to identify which islands can most effectively support waterbird nesting, taking into account biological, geographical, and economic factors. This pilot study, funded by the Knobloch Family Foundation, created the initial framework for a tool that will enable stakeholders to focus conservation efforts on the best outcomes for colonial-nesting waterbirds along the Texas coast.

The project focuses on five representative focal species: Reddish Egret (Egretta rufescens), Great Egret (Ardea alba), Tricolored Heron (Egretta tricolor), Black Skimmer (Rhynchops niger), and Caspian Tern (Hydroprogne caspia), each of which has different habitat and foraging strategies. The Reddish Egret, Tricolored Heron, and Black Skimmer are identified as high priority conservation species, while the Great Egret serves as an important indicator of the Gulf's health.

Methods

Screening Model - We assembled traits associated with colony persistence and size from ~45 years of data for the Texas coast combined with expert knowledge to produce a screening model that prioritizes existing islands or candidate sites for enhancement. Data associated with this screening model included:

• Waterbird population data from 19 breeding seasons (2003-2021) on 162 rookery islands between the Lower Laguna Madre and Redfish Bay

• Area of vegetated and bare substrate on 224 islands from four years of NAIP imagery between 1995 and 2018 delineated in GIS software to calculate the change in area of available nesting habitat and island size over time.

• An index of human disturbance on rookery islands based on proximity to busy boat ramps

• An index of predation on rookery islands based on proximity to land

• A Texas Parks and Wildlife Department fish and marine arthropod dataset used to estimate prey densities surrounding each island

• An index of any given island’s potential benefit for waterbird populations based on various characteristics compared between restored and unrestored scenarios

Foraging Habitat - We fitted GPS/GSM tracking devices to 32 birds in our study area and leveraged existing movement data for Reddish Egret and Black Skimmer to identify distances that focal species will fly to access foraging habitat and to determine core foraging areas. These data were implemented into a bioenergetic-based model that established the carrying capacity of the region.

Productivity - We surveyed 6 colonies weekly throughout the breeding seasons of 2021 - 2023 with a small Unmanned Aerial System (sUAS) and high-resolution camera operated at an altitude of 50m to determine nest survival and number of fledglings produced.

Prioritization Tool - The above datasets were used to develop a GIS-based prioritization model that describes the relative suitability of 162 rookery islands for island rehabilitation on a 90-mile portion of the Texas coast from Mission-Aransas Bay through the upper Laguna Madre.