The scaling back of Project Wing’s efforts is reportedly part of wider budget cuts being made to X, the experimental unit of Alphabet that focuses on so-called “moonshot” projects.

After Vos left, Alphabet did not name a successor. The project now reports to Astro Teller, the longtime chief of X. Vos did not immediately respond to emails seeking comment on Tuesday.

A sign at the Googleplex in Menlo Park, Calif., on Nov. 4. Google’s parent, Alphabet, has pushed out two leaders of its drone-delivery project. Photo: JOSH EDELSON/Agence France-Presse/Getty Images ...