SEXUAL SELECTION AGAINST HYBRID MALES

For pooled values, the pairing success rate for male Golden-winged Warblers was 83% and for male Brewster’s Warblers was 54% (Table 3), a highly significant difference (χ2 = 44.35, p< 0.0001). When analyzing individual study areas male Golden-winged Warblers also had higher pairing success than male Brewster’s Warblers (Table 3; two-tailed, paired t -test: df = 8,t = 3.25, p = 0.012). The pairing success rate for male Blue-winged Warblers at 77% also was highly, significantly greater than for male Brewster’s Warblers (Table 3; χ2 = 19.16,p < 0.0001). This difference was also present when analyzing individual study areas (Table 3; df = 7, t = 2.53,p = 0.039). The proportion of male Brewster’s Warblers that did not form a social pair (46%) is 2.7-fold greater than for Golden-winged Warblers (17%), and 2-fold greater than for Blue-winged Warblers (23%). Consistent with these data, we found evidence for sexual selection against hybrids overall (mean: 0.138; lower 95% CI: 0.045; upper 95% CI: 0.294). See Fig. 2.The strength of sexual selection against hybrids varied across study areas (range: 0 - 0.409), although this variance would be expected as a consequence of the very small sample of hybrids in each study.