Table 2.

Logistic regression models for dichotomous antipredator behaviors of mainland (N = 20) and Santa Catalina Island (N = 10), California, USA, populations of the southern Pacific rattlesnake (Crotalus helleri).

Predictors a	B	SE	Wald	p-Value	Odds Ratio (95% C.I.)
Rattle before grasping (χ23 = 2.55, p = 0.47, Nagelkerke R2 = 0.11, 56.7% predicted correctly)
Population	1.08	1.24	0.93	0.336	2.95 (0.33–26.70)
Snake length	−0.09	0.07	2.05	0.153	0.91 (0.80–1.04)
Duration captivity	0.002	0.05	0.00	0.961	1.00 (0.91–1.10)
Rattle during grasping (χ23 = 2.51, p = 0.47, Nagelkerke R2 = 0.15, 86.7% predicted correctly)
Population	2.50	2.16	1.33	0.248	12.12 (0.18–838.97)
Snake length	−0.12	0.12	0.94	0.333	0.89 (0.70–1.13)
Duration captivity	−0.05	0.08	0.42	0.518	0.95 (0.82–1.11)
Rattle during extraction (χ23 = 1.11, p = 0.78, Nagelkerke R2 = 0.06, 76.7% predicted correctly)
Population	0.30	1.18	0.06	0.800	1.35 (0.13–13.51)
Snake length	0.02	0.07	0.10	0.754	1.02 (0.89–1.17)
Duration captivity	−0.05	0.06	0.70	0.402	0.95 (0.85–1.07)
Cloacal gland discharge (χ23 = 1.33, p = 0.72, Nagelkerke R2 = 0.08, 86.7% predicted correctly)
Population	−0.60	1.74	0.12	0.729	0.55 (0.18–16.65)
Snake length	0.08	010	0.79	0.374	1.09 (0.90–1.31)
Duration captivity	−0.05	0.07	0.56	0.456	0.95 (0.83–1.09)
Attempted to bite (χ23 = 10.55, p = 0.014, Nagelkerke R2 = 0.41, 80.0% predicted correctly)
Population	−4.06	1.81	5.06	0.024	0.02 (0.00–0.59)
Snake length	0.11	0.10	1.21	0.272	1.12 (0.92–1.35)
Duration captivity	−0.01	0.06	0.04	0.837	0.99 (0.88–1.11)

^a Snake size and duration in captivity were treated as continuous variables.