The founder of Bird, a year-old scooter rental service that has attracted $450 million from investors, including Sequoia Capital, already has sold some of his shares, according to people who were briefed on the unusual move. A regulatory filing suggests that the founder, Travis VanderZanden, might have received at least several tens of millions of dollars from the sale, but the exact size of the sale couldn’t be learned.

Since June 1, the number of Bird shares described as “founders preferred stock” has dropped by one-third, to nearly 7.5 million shares from 11.25 million previously, according to a filing made Friday, provided by financial firm Lagniappe Labs. As Mr. VanderZanden is the sole founder of the company, he is the most likely holder of the founder-preferred stock. The drop would be equivalent to about $44 million if the shares were sold at the same price as the company’s most recent fundraising round, or $11.75 per share. Founder-preferred stock now accounts for about 4% of the company, down from about 7% as of June 1.