There are several areas where variants on the Bowdler surname have occurred.
Baldwin who came to England in 1105 was from the Flemish town of Boelare so he was Baldwin of Boelare. His name has been recorded in a number of spellings in a Norman form. The preceding 'De' is simply the Norman for 'of', the main surname was then Norman phonetic variations of Boelare.
In the 15th century, a branch of the Bowdler family who lived on a Ridge, then adopted this as their name. Later in the 17th century their descendants moved back to the Bowdler name and these are the Marton/Meadowtown Bowdlers.
In the 17th century, brothers John and Thomas Bowdler from Shropshire emmigrated to the Maryland Colony. Over time, they and their descendants dropped the 'r' and became the Bowdle family.