Sample sizes: S. Miguel, n=31; S. Rosa, n=10; S. Cruz, n=5; S. Catalina, n=6; S. Clemente, n=24; S. Nicolas, n=43; all islands, n=119; gray foxes, n=44; Isle Royale wolves, n=36. See also Table S5. (A) Incidence of congenital defects in gray and island foxes (this study), compared to Isle Royale wolves *[15]. (B) Incidence of traffic-related pathologies in gray and island foxes. **Absence of traffic-related pathologies in gray foxes possibly due to ascertainment bias against retrieval of mainland fox road kill.