Theses and Dissertations - UTB/UTPA
Using the spot-mapping censusing technique to assess changes in breeding bird communities at Santa Ana National Wildlife Refuge, Alamo, Texas, 1940-1996
Date of Award
Master of Science (MS)
Dr. Timothy Brush
Dr. Robert I. Lonard
Dr. Terry C. Allison
Results of breeding-bird censuses done by Davis in 1940 and by Gehlbach between 1973-1978 at Santa Ana National Wildlife, Alamo Texas, were compared to a 1995-1996 bird survey done in Gehlbach's study area. According to the Wilcoxon rank-sum test, bird densities in 1940 and 1995-1996 were similar, while 1973-1978 densities were lower. The 1995-1996 bird community was 76% similar to both the earlier studies. However, the communities studied in 1940 and 1973-1978 had only a 60% similarity. Negligible differences in bird densities and species composition were found between the 1995 and 1996 communities. Differences are attributed to changes in vegetation structure due mainly to habitat type and the effects of drought and freezes. Vegetational sampling revealed a decline in numbers of large trees in 1995-1996 compared to 1973-1978. Changes in vegetation have allowed birds that prefer thornscrub to increase their numbers, while those that rely on taller trees have decreased.
University of Texas-Pan American
Copyright 1996 Alberto Cantu. All Rights Reserved.