Evaluation of White-tailed Deer Response to Precipitation and Vegetation in McMullen County, Texas
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The purpose of this study was to examine vegetation and white-tailed deer (Odocoileus virginianus) responses to precipitation in McMullen County, South Texas. Understanding how deer respond to drought is especially important in a drought-prone region. Vegetation was assessed using the Normalized Difference Vegetation Index (NDVI) from level 1 Landsat 5 imagery, and deer records were donated from seven anonymous ranches on Managed Lands Deer Permit (MLDP) programs within the county. The variables analyzed from the deer records were fawn-to-doe ratios (fawn crop/recruitment), body weights, and antler measurements. Results indicate that fawn crop was strongly related to spring NDVI (r = 0.9; p ≤ 0.05) and summer (r = 0.9; p ≤ 0.05), spring-summer (r = 0.9; p ≤ 0.05), March-July (r = 0.9; p ≤ 0.05), and July-August (r = 0.9; p ≤ 0.05) rainfall. This positive relationship may be attributed to enhanced nutrition and fawning cover. Mature male body weights were related to summer (r = 0.9; p ≤ 0.05), spring-summer (r = 0.9; p ≤ 0.05), March-July (r = 0.9; p ≤ 0.05), and July-August (r = 0.9; p ≤ 0.05) rainfall. Additionally, mature males demonstrated a connection between Boone and Crockett score and summer (r = 1.0; p ≤ 0.01) and July-August (r = 1.0; p ≤ 0.01) rainfall. Spring NDVI was related to spring rainfall (r = 0.9; p ≤ 0.05), though summer NDVI did not indicate a relationship with summer rainfall. Spring NDVI was also strongly correlated to mature male body weights (r = 0.9; p ≤ 0.05) and main beam length (r = 1.0; p ≤ 0.01). Because of incomplete harvest records, analysis of physiological characteristics such as body weights and antler measurements was limited to the combined ranch averages. Also because of a low number of time-series, five years, a nonparametric statistical analysis using the Spearman r was the analysis performed for every relationship. The Spearman calculated strength of relationship by using ranks of values. Understanding how deer respond to periods of drought or periods of high rainfall in this part of Texas may provide landowners and land managers a more accurate assessment of what their herds will look like months in advance.