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

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.