"It seems some nests only appear every other migration"

#PokemonGO: I apologize if this has been discussed before. I tried searching before posting, but it's possible I didn't get the keywords right.I have been following the nest closest to my house for the past 7 migrations. I noticed that the area is only a nest every other migration. It went Doduo > no nest > Pinsir > no nest > Scyther > no nest > Magnemite. Has this been observed anywhere else? Could there be other patterns for nests out there?I thought about the possibility that the off-times were just nests of commons, but that didn't seem to be the case. I didn't see any increase in a specific common during those times. They were spawning with a pretty even mix. via /r/TheSilphRoad http://ift.tt/2gFqtPX