If you have many different calendars in the Calendar app, your screen might appear cluttered, making it difficult to find what you are looking for. For instance, you might want to see only all upcoming birthdays for the current month and not all of the other events on your calendar. To quickly hide all the calendars except for one, hold down the ⌘ key and then click the checkbox for any calendar to deselect all of your calendars. Then, click the checkbox for the calendar you want to display. Events only for that calendar will appear.
To redisplay all of your other calendars, hold down the ⌘ key again and click the checkbox next to any of the other calendars. All of your other calendars will once again be selected.