Rattata, Pidgey now appear less often in Pokémon GO
Server-side changes have been applied to Pokémon GO which make common Pokémon appear less frequently.
Additionally, Rattata and Pidgey can now no longer hatch from newly obtained Eggs. 5 km Eggs can now hatch into Eevee; previously it could only be hatched from 10 km Eggs. The distance needed to walk to obtain Candy with Rattata, Pidgey, or Eevee as the Buddy Pokémon (which corresponds to Egg distance) remains unchanged.
These changes are now live, and do not require an update.