cerc.usgs.gov
Over the last five years the Brazos Field Research Station research with swallows along the Rio Grande has resulted in the following four projects:
• Cave and Cliff Swallows as Indicators of Exposure and Effects of Environmental Contaminants on Birds from the Rio Grande, Texas (1999-2001) Master’s Thesis by: Daniel Musquiz, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, 77843-2258.
Cave (Petrochelidon fulva) and cliff swallows (P. pyrrhonota) were collected during 1999 and 2000 along the Texas segment of the Rio Grande and were used as potential indicators of local environmental contamination. Cave and cliff swallows were obtained from 8 sites along the Rio Grande from Brownsville to El Paso, Texas, and 1 reference site in Burleson County, 320 miles north of the nearest site on the Rio Grande. Blood samples were analyzed for variations in DNA content by flow cytometry, a technique that allows the detection of DNA damage in blood or other tissues. Plasma samples were analyzed for thyroid hormone (T3 and T4) levels using a radioimmunoassay technique. There were no sex-related differences in chromosome damage in both cliff and cave swallows. Cave swallows from the Del Rio area had the highest levels of DNA variation, which may be indicative of DNA damage. PAHs may have been a potential source for DNA damage; however previous studies indicate that sediment samples from tributaries near Del Rio have had the second highest chromium levels compared to other sites along the Rio Grande. Cliff swallows from El Paso had the highest levels of DNA variation, probably due to historic exposure to trace metals and possibly PAHs, while the reference site near Somerville had the lowest. T3 levels in birds from Llano Grande Lake were 3-fold higher between sampling years, while the neighboring site in Pharr-San Juan maintained identical levels. The only sex-related differences in thyroid hormone levels were found in El Paso birds, where female cave swallows exhibited higher levels of T3 hormones, and cliff swallows had higher levels of T3:T4 ratios. The causes for these results are currently unknown and merit further investigation. These data were also useful in establishing baseline data and evaluating several patterns that were evident from flow cytometry results. Areas of concern based on hormone and genetic data obtained in this study include Brownsville, Llano Grande Lake, Pharr-San Juan, Del Rio, and El Paso.
• Regional Variation and Relationships between DDE and Selenium and Stable Isotopes in Swallows Nesting along the Rio Grande and one Reference Site, Texas, USA Manuscript to be submitted to “Isotopes in Environmental and Health Studies”
Collaborators: Thomas W. Boutton, Department of Rangeland Ecology and Management, Texas A&M University, College Station, Texas.
Daniel Musquiz, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX.
Cave and cliff swallows were collected during 1999 and 2000 from eight locations along the Rio Grande (same swallows collected in previous study) to determine if δ15N and δ13C values could be used to predict DDE and Se contaminant burdens in insectivorous birds nesting across a geographic gradient in the Texas-Mexico border and to discern if stable isotopes could help discriminate between local versus non-local acquisition of contaminants. We analyzed δ15N and δ13C in liver and muscle, and DDE and Se in swallow carcasses. Within individuals, δ15N was higher in liver than in muscle of both species by an average of 1.34 ‰, whereas δ13C was 0.145 ‰ higher in muscle than in liver. Significant differences occurred among locations in δ15N and δ13C values in liver and muscle of both species. Cave swallows from three locations in the lower Rio Grande Valley were more enriched in δ15N than swallows from other sites. In general, swallows nesting in more northern latitudes along the Rio Grande had lower δ15N and δ13C values than those nesting farther south. Concentrations of DDE were significantly greater in swallows from El Paso, Llano Grande, and Pharr than in those from Brownsville, Falcon Lake, Laredo, Del Rio, and a reference site outside the Rio Grande. All swallows (N=21) from El Paso, Llano Grande and Pharr had DDE concentrations ≥ 3 µg/g ww, a value three times greater than the estimated threshold in avian prey that could cause potential reproductive failures in raptors. Concentrations of Se also were significantly greater in El Paso and Del Rio than at other locations. Most Se concentrations were not of concern for direct effects on birds or their predators. Principal component analysis indicated some positive correlations between δ15N and δ13C values in tissues and contaminant concentrations in carcass; however, analysis of covariance suggested a stronger effect of location on concentrations of DDE and Se. At the local level (Llano Grande and Pharr) there was a significant positive correlation between δ15N in liver and DDE concentrations in swallow carcasses; however, Se concentrations were not significantly correlated with isotopes even at the local level. Our results provide a good database of δ15N and δ13C values for insectivorous birds nesting along the Rio Grande. Similar ecologies for cave and cliff swallows and their abundance and wide distribution along the Rio Grande, make them ideal indicators of environmental pollution of this portion of the U.S.-Mexico border.
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Biomarkers and Environmental Contaminants in Swallows Nesting along the Rio Grande and a Reference Site, Texas, USA This is a manuscript that contains some data from the previous thesis above but also inorganic and organic data and cholinesterase measurements in brain.
Collaborators: Daniel Musquiz2, John W. Bickham2, Duncan S. MacKenzie3 Michael Hooper4, Judi Sabo4, and Cole Matson2 2 Department of Wildlife and Fisheries Sciences, 2258 TAMU, Texas A&M University, College Station, Texas, 77843-2258, USA 3 Department of Biology, Texas A&M University, 3258 TAMU, College Station, Texas, 77843-3258, USA 4 The Institute of Environmental and Human Health, Texas Tech University, Lubbock, Texas
This manuscript presents information on flow cytometry, thyroid hormones, cholinesterase activity, inorganic and organic contaminants in swallows. We analyzed differences among locations and relationships between biomarkers, morphometric values and contaminants. One of the most important findings of this study is that swallows and other birds nesting along the Rio Grande east of El Paso may be impacted by contaminants as reflected by a decrease in spleen mass (relative to other locations) and significant relationships with higher concentrations of DDE and most of the metals and metalloids.
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Environmental pollution of the Rio Grande: Are Current Pollutant Levels Affecting DNA and P-450 Aromatase Activity in Swallows? Master’s Thesis project by Megan Sitzlar, Department of Wildlife and Fisheries Sciences, 2258 TAMU, Texas A&M University, CollegeStation, Texas, 77843-2258, USA
Collaborators: Fuller Bazer, Department of Biochemistry, Texas A&M University, College Station, Texas John Bickham, Department of Wildlife and Fisheries Sciences, 2258 TAMU, Texas A&M University, College Station, Texas, 77843-2258, USA
We collected swallows in the Lower Rio Grande Valley during the 2003 breeding season. We analyzed P-450 aromatase activity in gonads and DNA damage by flow cytometry. We detected some gender and location differences in P-450 aromatase activity. The results are analyzed and writing is in progress. Master’s thesis is in preparation.
