TEXAS ORNITHOLOGICAL SOCIETY
SCIENCE SESSION
PAWS AND TAWS CONVENTION CENTER
ROCKPORT, TEXAS
15 April 2010
AGENDA
2:30 pm. CHARATERIZATION OF REDDISH EGRET FORAGING HABITAT AND BEHAVIOR IN THE LAGUNA MADRE OF TEXAS – ELIZABETH M. BATES
3:00 p.m. RAINFALL EFFECT ON CATCH RATES OF BUFF-BELLIED AND RUBY-THROATED HUMMINGBIRDS – BRENT ORTEGO
3:30 p.m. BIRDS AND VEGETATIVE CHARACTERISTICS OF NATIVE AND EXOTIC GRASSLANDS ON U.S. NAVY FACILITIES IN SOUTHERN TEXAS – MARC C. WOODIN
4:00 p.m. 2009 WINTER TEXAS GULF COAST AERIAL SHOREBIRD SURVEY – BRENT ORTEGO
4:30 p.m. INTERNATIONAL SHOREBIRD CONSERVATION PLANS -BRENT ORTEGO
CHARATERIZATION OF REDDISH EGRET FORAGING HABITAT AND BEHAVIOR IN THE LAGUNA MADRE OF TEXAS
ELIZABETH M. BATES*, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA
BART M. BALLARD, Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA
Abstract: The Reddish Egret (Egretta rufescens) is arguably the rarest species of heron in North America and little is known about its ecology. It is restricted to coastal habitat found primarily along the Gulf of Mexico. The majority of the breeding population occurs along the Texas Coast with greatest concentrations occurring in the Laguna Madre of Texas. Successful management of Reddish Egrets depends on having a clear understanding of habitat requirements. Our research objectives were to delineate foraging habitat based on water depth and substrate characteristics and evaluate the relationship between foraging tactics employed and environmental conditions. We recorded 20-min foraging bouts by 301 Reddish Egrets to assess types and success of foraging tactics used. Environmental variables measured at each site that we recorded foraging behavior included water depth, seagrass coverage, ambient light, and wind speed. We also recorded age and color morph of each individual. The average water depth was 4.70 inches and average seagrass coverage was 17 percent. There was no difference between color morphs for water depth or seagrass coverage. Eight foraging behaviors were identified. We modeled foraging behavior in relation to environmental variables using canonical correlation analysis for 36 individuals. The habitat variates created in the canonical correlation analysis were not effective at explaining the variation in the foraging behavior data suggesting other variables may be better indicators of foraging behavior.
RAINFALL EFFECT ON CATCH RATES OF BUFF-BELLIED AND RUBY-THROATED HUMMINGBIRDS
BRENT ORTEGO*, 202 Camino Drive, Victoria, TX 77905
BRON ROREX, 122 Cedar Ridge, Rockport, TX 78382
Hummingbirds were captured using mist-nets during 100 days each year from 2004 thru 2008. Netting effort was consistent at baited sites which contained 25 hummingbird feeders during summer, 50 during migration periods and 75 during winter. We averaged banding 142 Buff-bellied (Amazilia yucatanensis) and 1852 Ruby-throated (Archilochus colubris) per year at out banding station in Victoria County, TX, near the central Texas Gulf Coast. The Buff-bellied Hummingbird is a year-round resident species with different populations using the site during winter, summer and migration. The Ruby-throated Hummingbird is primarily a migrant at this site with only a few individuals trying to breed each year. January – May and annual rainfall accumulations were negatively correlated with capture rates of both species. Amount of precipitation is also directly related to availability of hummingbird flowers in the area which consisted primarily of red sage (Salvia coccinea), morning-glory (Ipomoea spp.) and Turk’s cap (Malvaviscus drummondii). Victoria County averages about 40 inches of rain annually, and commonly has very dry seasons which limits floral production. It was our experience that we received less visitations to the banding station as the availability of native flowers increased across the landscape. It is difficult to use capture rates of species at baited sites to accurately monitor population trends.
BIRDS AND VEGETATIVE CHARACTERISTICS OF NATIVE AND EXOTIC GRASSLANDS ON U.S. NAVY FACILITIES IN SOUTHERN TEXAS.
MARC C. WOODIN*and MARY KAY SKORUPPA, U.S. Geological Survey, Corpus Christi, TX.
Beginning in the 1800s and extending into the first half of the twentieth century, a large number of exotic grass species have been introduced into southern Texas to improve cattle forage. The effects of exotic grasses on grassland birds wintering in southern Texas have not been investigated. During 2002-2008, we collected data on measures of vegetation structure, density, floral diversity, seed resources, and bird use of native and exotic grasslands on five U.S. Navy facilities in southern Texas. Exotic grasslands were characterized by more grass cover, greater vegetative density, and greater seed biomass availability than native grasslands, whereas native grasslands were characterized by greater forb cover, more bare ground, greater seed diversity, and higher plant species richness than exotic grasslands. Bird surveys along transects in native and exotic grasslands showed that bird species richness was greater in native than in exotic grasslands, although bird numbers, at least in some winters, can be greater in exotic grasslands. Our results suggest that native and exotic grasslands may be contributing in different ways to maintaining winter bird populations in southern Texas.
2009 WINTER TEXAS GULF COAST AERIAL SHOREBIRD SURVEY.
BRENT ORTEGO*, Texas Parks and Wildlife Department, 2805 N. Navarro, Suite 600B, Victoria, TX 77901
MARC EALY, Texas Parks and Wildlife Department, 1700 7th Street (Room 101), Bay City, TX 77414
As part of a cooperative effort of southeastern states, we conducted an aerial survey from 9-17 February 2009 to determine major winter concentration areas for shorebirds along the Texas Gulf Coast. Shorebirds were surveyed from a Partenavia P-68 based out of Victoria with two observers viewing on either side of the airplane while flying at an altitude of 30 m (100 ft.) and flight speed of 185 km/h (100 knots). Shorebirds were placed into size categories when counted because of difficulty of identifying the birds to species under the conditions of the survey, but were tallied to species where possible. All likely high shorebird concentration areas within tidal zones were searched between the Sabine and Rio Grande Rivers. Approximately 1/3 of the major tidal marsh areas were
surveyed due to limitation of available air time. Only freshwater wetlands adjacent to tidal marshes were surveyed. Five airplane hours were used surveying Sabine Lake to High Island, seven hours surveying Galveston and Matagorda Bays, six hours surveying San Antonio Bay and Matagorda & San Jose Islands, three hours surveying Nueces & Corpus Christi Bays, and Mustang Island, and nine hours surveying Baffin Bay and Laguna Madre. Five K (thousand) shorebirds were found between the Sabine River and High Island, 45 K in the Galveston Bay complex with 16 K at Bolivar Flats, 11 K in the marshes west of Texas City and 7 K at the mouth of the Trinity River. Thirty-eight K were found near Matagorda Bay with 11 K being at the mouth of the Colorado River. Forty-six K were counted on Matagorda & San Jose Islands, and San Antonio Bay with 16 K on Matagorda Island. The Nueces & Corpus Christi Bays, and Mustang Island only had 2500 during the survey. The Laguna Madre system had the vast majority of birds with 89 K being on the Upper Laguna Madre and Baffin Bay with 60 K being concentrated in the “9-mile Hole” and 11 K along Baffin Bay. The Lower Laguna Madre had 95 K with 68 K using tidal areas between Port Mansfield and the Arroyo Colorado. The 330,000 shorebirds were comprised of 257 K small sized, 33 K medium sized, and 1 K large sized. There also were 14 K American Avocets (Recurvirosta americana), 4 K Willet (Catoptrophorus semipalmatus), and 1200 Marbled Godwit (Limosa fedoa). Ground surveys conducted during the same time indicated that the bulk of the small shorebirds were Western Sandpiper (Calidris mauri) and Dunlin (Calidris alpine), and the medium shorebirds being comprised of mostly dowitchers (Limnodromus spp.). The density and distribution of wintering shorebirds found during this survey contributes greatly to the knowledge of conservation planners to assist in focusing their efforts on habitat conservation.
INTERNATIONAL SHOREBIRD CONSERVATION PLANS
BRENT ORTEGO, 2805 N. Navarro, Suite 600B, Victoria, TX 77901
As North America moves forward in “All Birds” conservation international plans are developed for individual species. Shorebird planning is much more advanced at this time than other species groups. Of the 39 species of shorebirds that occurs in abundances large enough to be considered for conservation in Texas, international plans have been developed for 18 of these (http://www.whsrn.org/conservation-plans). Plans identified that there are huge information gaps in our knowledge of these species and Texas is not represented very well in many of these plans because not much research has been devoted to shorebirds in Texas. Status and information needs of Wilson’s Plover (Charadrius wilsonia), Piping Plover (Charadrius melodus), Mountain Plover (Charadrius montanus), Long-billed Curlew (Numenius americanus), Red Knot (Calidris canutus) and Buff-breasted Sandpiper (Tryngites subruficollis) will be discussed.
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