daily knowledge: in the days when twitter was still young, twitter's official logo was a bubbly blue wordmark spelling out the name of the service. however, the image of a blue bird was adopted by the community as a way to represent the service prior to the company ever designing a bird logo officially. this idea was solidified by twitterrific, a 3rd party mobile client for twitter developed by the iconfactory. it came out early in the site's lifespan and quickly gained notoriety as being the defacto twitter client prior to twitter ever shipping one themselves. 
Fun Fact
Not only did Twitter not have an official client originally, but the client in use today can be traced back to another popular client, Tweetie, which Twitter bought and rebranded. Twitter never technically shipped a client at all when the Twitter app was released.
In fact, if you ever find a way at poking around at the iOS bundle, or view its info manifest via the Mac app, it still calls itself com.atebits.Tweetie2. Due to how iOS apps work, you can't rename an app's bundle identifier whilst maintaining the same listing, so to this day the Twitter app is internally labeled Tweetie 2 on Apple devices.
