What code navigation strategies do developers use and what mechanisms do they employ to find relevant information? Do their strategies evolve over the course of longer tasks? Answers to these questions can provide insight to educators and software tool designers to support a wide variety of programmers as they tackle increasingly-complex software systems. However, little research to date has measured developers’ code navigation strategies in ecologically-valid settings, or analyzed how strategies progressed throughout a maintenance task. We propose a novel experimental design that more accurately represents the software maintenance process in terms of software complexity and IDE interactions. Using this framework, we conduct an eye-tracking study (n=36) of realistic bug-fixing tasks, dynamically and empirically identifying relevant code areas. We introduce a three-phase model to characterize developers’ navigation behavior supported by statistical variations in eye movements over time. We also propose quantifiable notion of “thrashing” with the code as a navigation activity. We find that thrashing is associated with lower effectiveness. Our results confirm that the relevance of various code elements changes over time, and that our proposed three-phase model is capable of capturing these significant changes. We discuss our findings and their implications for tool designers, educators, and the research community.