Bootstrap Site Needs Menu animated

We're looking for a developer to help animate a navigation. There are two images attached to this post. The [login to view URL] is what our menu looks like currently and is our start position. [login to view URL] is what we'd like it to look like, our end position. [login to view URL] is actually the mobile version of the navigation menu which you can view from any mobile device or you can resize your browser. Here's what we'd like to happen. The page first loads and the menu appears as normal. When the user starts scrolling downward, the menu will collapse itself. This has to be animated somehow. Maybe have the menu collapse from the start position and when it gets small enough, the end navigation appears. We’ll leave it up to the developer to determine the best way to do this. If we like it, we will keep it. This change only applies to desktop view (not mobile view). Please do not affect current mobile navigation/behavior. This is a bootstrap site. Coding must be clean. At the completion, developer must let us know which files were edited. We will provide source files. Animation must work on all major browsers.