Browsing by Subject "Waterfowl -- Texas"
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Item A time budget study of mallards on the Texas High Plains(Texas Tech University, 1985-08) Lee, Sang DonThe playas of the Southern High Plains (SHP) are important habitat for wintering waterfowl. In years of adequate rainfall, wintering waterfowl populations can exceed 1 million birds on the SHP. However, the recent trend toward playa modification for agricultural use is threatening waterfowl habitat in this region. Diurnal activity budgets of wintering mallards were conducted (1 October-31 March, 1983-1984;1984-85) to test differences among activity patterns at 3 habitat types; steep-sided pits, terraced pits, and open lakes. All seven activity patterns were different (P <0.05) among the 3 habitat types for wintering mallards on the SHP of Texas. Terraced pits had the greatest feeding activity (27.8%) and were higher (P <0.001) than steep-sided pits (11.2%) or open lakes (2.6%) even though the latter have an abundance of macroinvertebrates. Hens fed more than drakes (P <0.05). Locomotion (32.2%) and alert (2.8%) behavior across the 3 habitat types showed the highest level during the early morning. Paired mallards rested more (37.9%) than unpaired mallards (25.8%) (P <0.05). Agonistic activity was highest (2.4%) in terraced pits throughout the season. This study suggests that wintering mallards will feed in lakes if food is available, thus potentially balancing a high corn diet.Item Factors associated with waterfowl botulism in the Southern High Plains of Texas(Texas Tech University, 1985-05) Thompson, G. KevinThis study was conducted on the Southern High Plains of Texas between 1 June 1982 and 1 November 1983 to monitor Clostridium botulinum type C toxin production, botulism in waterfowl, and populations of macroinvertebrates in playa lakes. Eight and 14 birds were found sick or dead on study lakes in 1982 and 1983, respectively. Six ducks, 3 in each year, were positive for botulism type C toxin. All study lakes had at least 1 duck that was positive for botulism. Four pintails (Anas acuta) (66%) one green-winged teal (A. crecca) (17%) and one mallard (A. platyrhynchos) (17%) contained C. botulinum In this study, most ducks died of botulism during September and October. However, one duck contracted botulism as early as 8 July in 1983. Thus, botulism has been observed during a 131-day period (8 July-15 November) in the Southern High Plains. Mean values for temperature, dissolved oxygen, and pH ranged between 11.0-32.0 C, 2.6-8.1 ppm, and 5.3-8.7, respectively, in playas with botulism-positive birds. One of 145 invertebrate samples tested for botulism was positive for toxin. Major invertebrate taxa collected included Chironomidae, Corixidae, Dytiscidae, Baetidae, Hydrophilidae, Gastropoda, and Oligochaeta. Although shorelines fluctuated throughout the most critical botulism periods (August-October) for this region, this was not associated with a drastic decline in numbers of a taxon or in total invertebrate abundances. Each lake contained 13 to 15 taxa of invertebrates during the study. The index for combined taxa abundance showed no significant (P>0.05) difference between years. Chironomids were the most dominant and influential constituent of playa benthic fauna. However, on one lake mayflies were the most abundant taxon. Except for Oligochaetes and leeches, no taxa showed significant differences between years. Abundances of several taxa (Chironomidae, Ephemeroptera, Gastropoda, Hydrophilidae, and Hirudinea) and total abundances had significant differences between playas while others (Chironomidae, Dytiscidae, Hydrophilidae, and Ephemeroptera) had abundances that differed between vegetation zones.Item Field-feeding ecology of waterfowl wintering on the Southern High Plains of Texas(Texas Tech University, 1982-08) Baldassarre, Guy AThe ecology of field-feeding dabbling ducks wintering on the Southern High Plains of Texas was studied on a 50 km2 study area in Castro County, from September-March 1979-82. Ducks relied primarily on waste corn that averaged 364 ± 12 kg/ha/field. Fields harvested at 14-21% moisture lost more than twice the corn as fields harvested at 22-36% moisture. Therefore, moisture content of corn at harvest provided a useful measure to predict initial waste. Waste cornfields underwent a variety of agricultural treatments that affected the abundance and availability of waste corn to waterfowl. Burning stubble maximized abundance and availability, whereas deep plowing reduced abundance by 97%. Disking and grazing reduced abundance by 77% and 84%, respectively. However, landowners tended to graze cattle on fields where initial waste was high and thus substantial amounts of waste corn remained when grazing was terminated. Manual salvage by migrant workers removed 58*^ of initial corn waste. Field-feeding waterfowl conducted 2 flights daily to cornfields near playa lakes where the birds concentrated. The average morning flight was initiated 52 ± 1.5 min before sunrise and terminated in 23 ± 1.4 min. The average evening flight began 25 ± 2.0 min after sunset and terminated in 37 ± 4.2 min with duration increasing as the season progressed. Dabbling ducks fed longer and participated more in evening as compared to concurrent daily morning flights. Minimum temperatures were correlated negatively with duration of evening flights, but not morning flights. There was no correlation between the amount of waste corn in, or the condition of, a field selected by feeding ducks with duration or initiation of feeding flights. However, the amount of corn present was correlated negatively with duration of the evening flight. Snowfall was positively correlated with duration of evening flights, but not morning flights. Feeding flocks selected fields based on an abundance/availability hierarchy, apparently attempting to minimize foraging time. Burned fields were preferred most when available, followed by disked fields, especially those containing >60 kg waste corn/ha. Field-feeding is an adaption to widespread agriculture, but also is a learned response to changes in wetland habitats.Item Numerical response of wintering waterfowl to macrohabitat in the southern High Plains of Texas(Texas Tech University, 1982-12) Obenberger, Susan MPopulations of pintails (Anas acuta), American wigeon (A. americana) , mallards (A. platyrhynchos) , and green-winged teal (_A. crecca) were studied on 10 23.04-km^2 plots in the Southern High Plains of Texas during September-March 1980-1981 and 1981-1982. Peak total populations occurred in November and February, largely because of massive influxes of pintails during these months. Mallard and wigeon populations were relatively stable after peak numbers arrived on the wintering areas and before spring migration. Sex ratios observed in this study were similar to those reported in other portions of the Southern High Plains. The estimated percentage of males was similar (P>0.05) each month during October-March for mallards and wigeon but was lower (P_< 0.05) in December 1981 (58%) than in January 1982 (70%) for pintails and in October-November 1980 (47-49%) than in December-March 1980-1981 (72-80%) for green-winged teal. Availability of waste corn in disced fields was relatively constant throughout the winter because as fields were plowed the stubble in other fields was disced. Less than 3% of the corn stubble was burned. Multiple regression models that predicted monthly waterfowl use of plots based on hectares of macrohabitat were acceptable for total ducks, wigeon, and pintails but were not acceptable for mallards and green-winged teal. Hectares of water, corn, and wheat positively affected waterfowl use whereas hectares of sorghum, cotton, and other land uses negatively affected waterfowl use. The models can be used to determine the most effective and cost-efficient management measures to increase or decrease waterfowl populations on wintering areas in the Southern High Plains of Texas.