I know that normal nocturnal bats can be seen flying at daytime sometimes during rare circumstances. But are there any flying mammals that have evolved to fly around during the day? Or have they all just decided not to compete with the birds in this regard?
I’d say flying foxes (giant bats/megabats) that are all around the Indian Ocean fit the definition of flying during the day. You can see them fly over Sydney at dusk every day. Also, I think some aren’t even considered nocturnal.