Websites that shorten URLs have become a hot category over the past few weeks, mostly due to the increasing popularity of Twitter and their use to fit URLs in tweets without going over the 140 character limit. One website, TinyURL has dominated this category and was the default URL shortening service for Twitter, until today when many noticed that TinyURL has been replaced by bit.ly. This switch is likely to have a strong and immediate impact upon the category where TinyURL was consistently the leader and captured 5.5x the volume of visits of bit.ly in April 2009.

The 2nd and 3rd ranked URL shortening services bit.ly and ow.ly both experienced significant growth in visits during April, with an increase of 200% for both websites as compared to the previous month. Visits to TinyURL also increased 6% during the same time frame. The reduced growth rate may be partly attributed to the fact that only half of TinyURL’s traffic was from new visitors (those who haven’t visited in the past 30 days) in April 2009, down from 65% in March 2009.

Overall it will be difficult to measure the impact of the new Twitter and bit.ly partnership due to the use of plug-ins within browsers and desktop applications, thus eliminating the need to visit the bit.ly website. However, Twitter is typically the top driver of traffic for the top URL shortening websites, so the new partnership is likely to reduce the share of referrals for several of the players. For example, ow.ly received 57% of their traffic d from Twitter in April 2009, which may need a workaround in the future to maintain growth.