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Among all migratory birds, grassland species have experienced the most significant declines in numbers, as their native habitats have been reduced in size and quality to mere fragments of what once existed. Conversion of native grassland to cropland and the modern custom of fire suppression have contributed to this drastic degradation of the prairies. In Texas, it is estimated that less than 1% of the high-quality coastal prairie existing before settlement still remains. Additional concerns in Texas are overgrazing and the predominance of exotic grass species introduced for use as forage. While grassland birds, as a group, are not well studied, most research has focused on breeding ecology. In contrast, grassland bird distribution, abundance, and ecology during winter remain poorly studied. For these reasons, the Texas Gulf Coast Field Station initiated winter surveys of grassland birds at the U.S. Fish and Wildlife Service Laguna Atascosa National Wildlife Refuge and Department of Defense facilities (Naval Air Station-Corpus Christi and Naval Air Station-Kingsville) in southern Texas.
Objectives of these studies are to assess the effect, if any, of grassland type (native grass vs. exotic grass), size, plant density, and vegetative diversity class (high or low) on grassland bird numbers and species composition. Bird surveys are conducted monthly along grassland transects (100 m x 20 m) from December through February. The surveys and vegetation sampling follow the Project Prairie Birds protocol (Texas Parks and Wildlife) for wintering grassland bird surveys along the Texas coast. An additional aspect of the Refuge study was to mist net grassland birds at selected transect sites during the winter survey period. Captured birds are fitted with leg bands, then released. Mist netting provides an opportunity to compare net results with transect results.
The most abundant bird species identified during the surveys are savannah sparrows and mourning doves. Other key species are sedge wrens, LeConte’s sparrows, grasshopper sparrows, Sprague's pipits, Lincoln’s sparrows, and olive sparrows. Common exotic grass species are buffelgrass (Pennisetum ciliare), Kleberg bluestem (Dichanthium annulatum), angleton bluestem (Dicanthium aristatum), johnsongrass (Sorghum halepense), guineagrass (Urochloa maxima), and bermudagrass (Cynodon dactylon). A variety of native grass species have been found, including Pappusgrass (Pappophorum vaginatum), Louisiana cupgrass (Eriochloa punctata), and Arizona cottontop (Digitaria californica), as well as the native salt-tolerant species (Spartina sp. and Sporobolus sp.). In general, areas dominated by exotic grass species have a low vegetative diversity (i.e., low number of plant species) and, in turn, support fewer animals. Upon completion of these studies, refuge and resource managers, will possess information on the need to control exotic grasses in Texas coastal prairies.
Project Prairie Birds link at Texas Parks and Wildlife: www.tpwd.state.tx.us/nature/birding/prairie_birds/index.htm
U.S.
Fish and Wildlife Service Laguna
Atascosa National Wildlife Refuge
Texas A&M University-Corpus Christi (TAMU-CC), Center
for Bioacoustics
U.S. Department of Defense, Legacy Program -- U.S. Navy
"USGS -
DoD Investigate Grassland Birds in Texas" USGS - DoD Science
Collaborator (April 2005)
Center
for Bioacoustics, TAMU-CC unless otherwise indicated)northern mockingbird showing south Texas habitat
eastern meadowlark just banded (photo by Jay Gardner, TAMU-CC)
thrashing the ground with long poles to flush sparrows for counting and identification
mist nets used to catch birds
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