The "Larry the Bird" mascot was introduced, and the wordmark revised, in September 2010.
A new bird was introduced in June 2012 which was facing up, and the name was lacked from the logo, leaving the icon to stand out on its own, the word "Twitter" and the lowercase letter "t" are now no longer used. The bird is now referred to as the "Twitter Bird".
The first Tweet icon used the "t" from the logo's wording. Still exists on some websites.
In 2010, the Tweet icon was revised with Larry the Bird in place of the "t".