If they are noticeably smaller than honeybees, they might be a solitary native bee species. My solitary bees are nesting now in my boxes, busily going back and forth, bringing in pollen. They are dark and fly fast and have a very hearty BUZZZ! So sweet!I was watching some bees flitting around various blossoms yesterday and again this morning. Small, dark bees with a hearty buzz to intimidate the non-admirers. Some had gathered quite a bit of pollen, a nice orange/brown. Are they satisfying some other beek? Ferals? Who knows.