The continuous evolution of Android operating system necessitates regular API updates, which may affect the functionality of Android apps. Recent studies investigated API evolution to ensure the reliability of Android apps; however, they focused on API methods alone while ignoring API fields. This paper presents an empirical study on the API field evolution and its induced compatibility issues. Our experimental results yield many interesting findings, e.g., on average two API field compatibility issues exists per app, different types of checks are preferred when addressing different types of compatibility issues, and fixing compatibility issues induced by API field evolution takes more time than fixing compatibility issues induced by API method evolution. These findings reveal the importance of incorporating API fields in future studies on API evolution, and will help developers and researchers in better understanding, detecting, and handling Android compatibility issues induced by API field evolution.