Pokémon Nests

Pokémon Nests are areas in specific geographical locations where an increased number of the same species of Pokémon appear for a short duration.

Nest migrations
Nest migrations are regular events in which a Pokémon nest changes to another location. A migration occurs every other Thursday between 0:00 UTC and 0:30 UTC. The migration is scheduled to occur on May.

In the early weeks of the game, the migrations occurred about once a month. Since October 2016, migrations have occurred bi-weekly on a regular schedule. When a batch of new Pokémon species are released, nests are usually changed immediately.

Below there is list of nests migrations that have previously occurred.

Trivia

 * Pokémon Nests are not clearly visible during the gameplay, but they are in places where the higher amount of spawnpoints for one specific Pokémon species occurs more than once.