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Diversity
- Texas A&M University Press
- Chapter
- Additional Information
diversity Because of the UTC’s geological heritage, it lacks many substrate types and elevational features that are known for their special bird assemblages—there are no talus slopes, mesas, volcanic islands, on- or offshore nesting cliffs, brushy slopes, or rain-shadow deserts. The UTC’s latitude precludes rain forest, tundra , and ice fields. Indeed, in a global sense, the lack of habitat diversity seems noteworthy. Since European settlement, those habitats that are present have been subjected to pesticides, logging, burning, farming , grazing, dredging, pollution, and siltation or have been buried under asphalt and concrete. Much of the natural vegetation has been removed or modified, and that which remains has suffered the intrusion of a host of exotic species. Farming practices and coastal development have either created or destroyed wetlands . The diking and draining of low-lying areas has changed the salinity and depth of coastal marshes, variously diminishing or improving their availability to birds. Naturally occurring fires have been suppressed , changing the species composition of both prairie and forest plants. Market hunting extinguished the bison and Passenger Pigeon in the region and seriously compromised bird species killed for their plumes; modern hunting as a management practice remains controversial. Why then, in the face of such apparent ecological adversity and human abuse, does the UTC offer a naturalist so many species of birds to study and enjoy? Among the various factors, we might cite the mild winters that provide arthropod and other invertebrate prey for a wide variety of species. The lack of snow makes seeds and fruit more available to doves, thrushes, waxwings, and finches. Ornamental plantings provide cover and many foods not present historically . Certain shorebirds profit from artificially flooded fields that might otherwise be dry, while other kinds feed in burned fields that might have been brushy. In the cities and suburbs, many species are provided nest sites and supplementary foods by home owners anxious to surround themselves with birds. In less disturbed areas, valuable habitats are being protected and enhanced as new sanctuaries and parks continue to appear across the UTC. The most important factor influencing the region ’s avian diversity, however, remains its special position relative to migratory routes and the surrounding avifaunas. Hundreds of thousands of ducks and geese that breed to the north arrive via the Central and Mississippi flyways, either wintering on or passing through the UTC. Each spring and fall, millions of songbirds cross the Gulf of Mexico, many pausing locally for rest, food, and water. Clouds of shorebirds migrating between the pampas of Argentina and Uruguay and the arctic tundra pause to gorge on the UTC’s marine and terrestrial invertebrates . Additionally, the area receives migrants, irregularly occurring rarities or vagrants, and very rare accidentals from surrounding zoogeographic regions. Table 3 summarizes the origins of representative birds occurring on the UTC. The factors that generated a local avifauna of over 480 species would seem to be solidly in place. Until recently, they were anchored to such truisms as: The habitats available to birds are endless and immutable . The migrations of birds are ancient; their return is as guaranteed as the phases of the moon. Climate is predictable; learn to live with it and we have nothing to fear. Resources are infinite; the earth will nourish its own. Two centuries ago, residents on the Upper Texas Coast might have been comfortable with these concepts. Now, each day, homeowners, farmers, conservationists, sportsmen, multinational companies , small businesses, and government realize the fallacy of such perspectives. Sadly, this realization does not always ensure the welfare of birds. The birdlife of the Texas coast survives both because of and in spite of the actions of the local human population. The U.S. Fish and Wildlife Service designates refuges for migrating waterfowl. At the same time, the goose prairies east and west of Houston disappear a thousand acres at a time under subdivisions . One administration is committed to protecting our coastal wetlands; another decides they should be developed. A thousand bird watchers plant hummingbird gardens, but the woodlands of Waller County are bladed flat for house trailer sites. A stretch of Galveston Island becomes a haven for diversity 17 migrating shorebirds while down the road, another home site covers precious habitat. Bird diversity on the Upper Texas Coast is inextricably linked to habitat diversity. Yes, it is true that there are more kinds of habitat on the UTC than Audubon encountered during the early 1800s (consider Houston—then a treeless marsh...