Survival and mammalian predation of Rio Grande Turkeys on the Edwards Plateau, Texas.



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Texas A&M University


Trends in Rio Grande wild turkey (Meleagris gallopavo intermedia) abundance on the Edwards Plateau (EP), Texas, have been either stable or in decline since the 1970s. Four study areas, 2 each within stable (Stable Area A, SAA; Stable Area B, SAB) and declining regions (Declining Area A, DAA; Declining Area B, DAB), were delineated to examine (1) both annual and seasonal survival, (2) relative mammalian predator mean abundance (RMA), and (3) potential effects of lunar phase on scent-station visitation. During February 2001-March 2003, 257 turkeys were captured and instrumented with radio transmitters. Survival probabilities were generated using a Kaplan-Meier product limit estimator; a log-rank test tested for differences among sites. Annual survival was statistically different between regions (stable 0.566 ? 0.081; declining 0.737 ? 0.094; X2 = 3.68, P = 0.055) in 2002. Seasonal survival differed between regions (stable 0.812 ? 0.103; declining 0.718 ? 0.130; X2 = 3.88, P = 0.049) in spring 2003. Annual survival results during 2002 were counterintuitive with turkey trend data. Scent-station transects were established on non-paved ranch roads within study regions. Scent-station indices revealed higher (H = 19.653, P ? 0.001) RMA of opossum (Didelphis virginiana) and skunk (eastern spotted [Spilogale putorius], striped [Mephitis mephitis], or western spotted [S. gracilis]) (SAA, x? = 0.0148; SAB, x? = 0.0151; DAA, x? = 0.0042; DAB, x? = 0.0065) on stable areas. Higher RMA of coyotes (Canis latrans) on declining areas (SAA, x? = 0.0067; SAB, x? = 0.0022; DAA x? = 0.0234; DAB x? = 0.0434) suggested a possible causative factor of the decline, but abundance indices were not verified by empirical data though. Lunar phase was not a significant (T = -0.225, P = 0.822) covariate in scent-station visits by raccoons, opossums (new, x? = 0.0111; full, x? = 0.0324), or unidentified tracks (new, x? = 0.0649; full, x? = 0.0375). Nightly precipitation and wind speed probably influence mammalian use of scent stations more so than lunar illumination.