Every couple weeks, the creators of "Pokemon Go" spice things up by shuffling around Pokemon spawn points - also called "nests" - to keep players guessing. Nests are areas located in the real world where a large number of a specific species of Pokemon will appear. For instance, if you arrive at a location and are suddenly surrounded by five or six Charmanders, that would mean you've wandered into a Charmander nest.

"Pokemon Go" creator Niantic Labs has tried to keep their augmented reality, free-to-play mobile game as realistic as possible by keeping in mind Pokemon types - which is why water-type Pokemon like Tentacool can be found near bodies of water. On the other hand, nests can pop up anywhere regardless of their real-world location or the Pokemon type.

The nests change every 22 to 24 days otherwise, there wouldn't be much challenge to hunting and finding specific Pokemon. "Pokemon Go" players call them migrations, and it's not uncommon for completely different Pokemon to take over old nests.

Here we go trainers! The 10th Migration went live an hour or so ago! Shoutout to the team @TheSilphRoad for the updates! #PokemonGO

— Pokémon Go Chicago (@PokemonGOChi) December 29, 2016

Knowing which Pokemon will replace what is not an exact science, but Heavy managed to list some of the more common changes through culled player reports via the "Pokemon Go" subreddit. For instance, Bulbasaurs seem to have taken over Pidgey nests, while Digletts have been spotted where Ghastly, Jynx, and Mankey used to spawn. Some players have also reported Voltorb spawning in known Magnemite nests.

Again, the list is based on player reports and not an official announcement. The actual migration changes may depend on where in the world you're located. The best way to get an idea of which Pokemon went where, you can check out The Silph Road - a location-based global nest atlas that records data from thousands of users to give players a more accurate map of real-world spawn points and nest behavior.

"Pokemon Go" may not be experiencing the same level of hype it garnered when it first launched, but it's still going strong. As one of the most-downloaded mobile games of 2016, loyal fans remain supportive and religiously await the next big update.