Impacts of Bridge Design and Land Cover Characteristics on Cliff Swallow Nesting
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The Texas Department of Transportation (TXDOT) and the Texas Commission on Environmental Quality (TCEQ) were concerned with the possible contamination of water resources resulting from animals roosting on bridges, particularly, from Cliff Swallows (The Texas Department of Transportation, 2012). Considering there are approximately fifty thousand bridges currently in Texas, these potential contamination sources could be an environmental problem. These bridges can offer thousands of potential nesting sites to Cliff Swallow colonies, which vary in size from 2 to 3700 nests (Brown & Brown, 2004). An assessment of 108 bridges was made to develop a model for predicting total Cliff Swallow nest density based on bridge characteristics and geographical information systems (GIS) land cover and soil data. Backwards step-wise regressions were run and then evaluated based on Akaike’s Information Criteria adjusted for small sample sizes (AICc) to determine the best model for analysis. This model indicated the number of nest scars, twenty-five degree bridge skew, average sand and silt percentages within the bridge surroundings, the number of spans, span length, and the percentage of water within the bridge surroundings is positively correlated with Cliff Swallow nest density, while bridge length, bridge orientation, fifteen degree bridge skew, bridge design, percentage of developed open land within the bridge surroundings, and percentage of shrubs within the bridge surroundings have a negative correlation.