I found the following information about choosing which operating system functions as the default:
10. How do I choose which operating system will start up my Mac?
After running Boot Camp Assistant and installing Microsoft Windows and Boot Camp drivers, press and hold the Option (Alt) key while you start up your Mac to switch between Microsoft Windows and Mac OS X operating systems. Use the Startup Disk control panel in Windows or Mac OS X Startup Disk preferences to set the default operating system to use each time the computer starts up.
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