late 14c., prollen, "move about in search of something," of unknown origin, with no known cognates. Meaning "go stealthily in search of prey" is first recorded 1580s. The noun, in on the prowl, is attested from 1803. Prowler is attested from 1519.
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with on the prowl
Actively looking for something, as in Their underpaid computer programmers are always on the prowl for better jobs. This idiom transfers an animal's search for prey to human pursuits that are usually less bloodthirsty.
[ c. 1800