The Bexar county bird checklist contains 426 species. This is close to half of all of the species of North America. This is an outstanding total species count for any county in the United States. A discussion about the causes of this diversity follows.

The essay that follows is copyrighted by Steven A. Hawkins. Reproduction rights are granted only for personal use. The San Antonio Audubon Society is authorized to use this essay for its web site.


On the Diversity of the Avifauna of Bexar County, Texas

San Antonio is located in Bexar County, Texas. Depending on a person's bias, it is variously described as being in south-central Texas or at the north end of South Texas. The fact that both descriptions fit is both a biological and a cultural phenomenon that makes for a very interesting county in which to bird and reside.

The diversity of habitat described below has resulted in a checklist that contains 426 species. As in real estate, the key to biological diversity is location, location, location.

Bexar County is about equidistant between Florida and California. It is close to where the Gulf coast makes its dramatic turn to the south towards Mexico. This results in a funneling effect that causes many species from the eastern part of North America to move westward in order to avoid flying over the Gulf. Conversely, Bexar County is far enough to the west for a number of species to reach their eastern extent here. Bexar County is far enough south for many northern species to spend their winters here, as many people do also.

Bexar County is at the juncture of three biological provinces: 1. The Blackland Prairie, a belt of prairie that reaches its southern end in eastern Bexar County. 2. The Edward's Plateau, which is a heavily eroded limestone uplift in Central Texas. 3. The Tamaulipan Biotic Province, named after the state of Tamaulipas of northeastern Mexico. It is also called the Tamaulipan Thorn Forest. Each of these biological communities has its components that add to the avifaunal richness of Bexar County.

The Blackland Prairie is surely the least birded of the three biotic provinces represented in Bexar County. Its species-Mountain Plovers, all of the longspurs, several species of sparrows-are some of the less dramatic species to be seen. The fact that open prairie tends to have smallish birds that disappear into the grass or the furrows in the fields combine for less birding. The fact that prairie tends to not be bought or given as park land adds to a lower amount of birder activity. When it is made into park land, it tends to be made into ball fields of one sort or another, none of which are particularly attractive to most species of birds.

The Edward's Plateau, by contrast, is heavily birded in the Spring. Two of the "glamour" species-Golden-cheeked Warbler, and Black-capped Vireo-nest on the Plateau. Friedrich County Park, in northern Bexar County, is a well know nesting site for Golden-cheeked Warblers. Black-capped Vireos nest there to a lesser degree. The Camp Bullis Military Reservation has good sized populations of both species. Since the passage of the Endangered Species Act, the military has monitored those endangered species on its reservations. Some of that information has made it into the SAAS bird records. There are several city-of-San-Antonio parks that are located on the Plateau. Although those parks tend to be dominated by ball fields, some of those parks have natural areas that have some real birding potential.

The Tamaulipan Thorn Forest is another "glamour area" for many people from outside of Texas. This is the part of Texas that gets the spill-over species from Mexico. Harris's Hawks and Crested Caracaras are two of the easier of such species to find. You throw in a mixture of Cactus Wrens, Long-billed and Curve-billed Thrashers, Bronzed Cowbirds, Verdins, etc. and you have an excited out-of-stater. Showing someone a male Vermilion Flycatcher for their lifer is usually good for a hand shake, if not a beer.

The Tamaulipan Thorn Forest is heavily birded because there are several parks of one kind or another in it. The two power plant lakes, Calaveras and Braunig, are located on the south side of San Antonio. The birding in the parks that are on the edges of those lakes gets us many of the Tamaulipan birds. The most heavily birded location in Bexar County, Mitchell Lake, is located on the south side of San Antonio.

Mitchell Lake has been birded since at least 1923, when Northern Jacanas were noted as nesting there. Generation after generation of birder has passed down word about the quality of the birding at the lake. This is in spite of the fact that Mitchell Lake was used as the main sewage lagoon for the City of San Antonio through the late 1970s or early 1980s. In spite of this abuse, Mitchell Lake has given birders such things as Ruff, Zone-tailed Hawk, Ross's Goose, Curlew Sandpiper, Sooty Tern, etc. The San Antonio Audubon Society has had field trips to Mitchell Lake since its founding in 1954. Those field trips became monthly around 1980. SAAS has not been shy about publicizing the birds seen at Mitchell. The result has been that similar to the picnic stop west of Patagonia, AZ. Fame has resulted in heavy birding, which has resulted in good birds being seen, which has resulted in even heavier birding activity.

San Antonio has always been one of the larger cities in Texas. This means that there have always been a comparatively large number of birdwatchers and birders who live in San Antonio. Birding activity tends to beget birding activity, which begets more birding activity, etc.

Comparative seasonal bird activity: Like many locations, Bexar County tends to have definite peaks and lows in avifaunal diversity. Some seasons get more of the 426 recorded species than others: Spring: 373 species; Summer: 272 species; Fall: 371 species; Winter: 336 species. Springtime is obviously the best time to bird Bexar County, although many of the glamour species are also seen in the Summer. Each of our species has its own timetable for getting things done.

Some species, such as Golden-cheeked Warblers arrive early (March) and return south early (late June-mid July). Some species arrive late: Groove-billed Anis do not nest until June or July. Shorebirds add to the confusion. The latest "Spring migrants" pass through in early June. The earliest "Fall migrants" come through during the 3rd week of July.

Of those 426 species that have been recorded for Bexar, 143 are know to have nested in the county. Only 114 currently are known to nest in Bexar County. That total could probably be increased by increased access to private land. That possibility is countered by the increasing urbanization of Bexar County that will almost certainly result in fewer nesting species of birds in Bexar County.

We invite you to share in the Bexar County birding adventure. Click on SAAS home page to see information about the San Antonio Audubon Society and to return to the main SAAS web site.

Good Birding!

Steve Hawkins


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