-a is the ending that carries best of all: it is open, it is loud, and it does not clip. 2,198 names here finish with it. It also reads as feminine to most English speakers, which the female dog names counts bear out — though the registers hold plenty of male animals with -a names.
Why do so many pet names end in A?
Because an open vowel at the end survives being shouted. It is the same reason -y and -ie endings are common: the last sound stays audible at a distance.
Are names ending in A always female?
No. The ending reads as feminine in English, but this catalogue records gender from how real animals were sexed, and plenty of -a names come back male or unisex.
Every count on this site is a tally of real registrations: pet licences and shelter intakes published as open data by New York, Seattle, Austin, Montgomery County, Cambridge, Zurich, Basel and three Australian councils. Popularity here is the average share a name holds across those registers, so a name common in a small city is not buried by one common in a large one. Nine of the eleven sources are North American, so read the ordering as naming in those places rather than worldwide. Browse the whole catalogue or read how the data is put together.