Island plants and animals often differ from their mainland relatives. Why? In general, isolated islands lack top predators and large herbivores, which can influence food chains and traits of island organisms. In addition, differences in human interactions and threats posed by pathogens and parasites can also contribute to variances in traits. In a case study involving eastern bluebirds, (Sialia sialis) researchers show just how island life shapes the physiology and life history of a species.