Final answer:
If a browser does not support the HTML5 search field, it defaults to displaying a standard text field.
Step-by-step explanation:
When a browser does not support the HTML5 search field input type, it defaults to displaying a text field instead. This behavior is part of HTML5's specification which promotes graceful degradation; this means that if a newer feature is not supported by a browser, the page will still work, but with a more basic functionality. In this case, the browser will show a regular text input because a text field is the default state for input tags when the specified type is not recognized.