On the eastern shore of Corpus Christi Bay lies one of the most important colonial bird-nesting islands on the Texas coast. The island was once an extensive peninsula of Mustang Island, but in the 1950s, a series of navigational channels were dug into the landmass, significantly weakening it. In early August of 1970, Hurricane Celia's path of destruction completely separated the peninsula into an island, creating a prime rookery nearly free of human disturbance and predatory wildlife. Nineteen bird species now nest on The Nature Conservancy's (TNC) 110-acre Shamrock Island Preserve each year, some of which have thousands of nesting pairs.
Grassland plants and shrubs help stabilize Shamrock Island's dunes and other substrates, slowing wind and water erosion. Seagrass meadows provide essential forage for redhead ducks, as well as nursery, foraging and refuge areas for many estuarine fish and invertebrates. In addition, resident and migratory species depend on the preserve’s land-based plants for nesting sites, food and shelter.
Among the plant communities of conservation interest are seaside little bluestem, gulfdune crowngrass, sea oats, shoal grass and Texas stonecrop. In addition, sand brazos-mint, crown coreopsis, velvet spurge, coastal plain umbrella-sedge, Jones' nailwort and Indianola beaksedge are also often found here.