According to /r/TheSilphRoad, multiple players reported catching Dragonites near Clefairy nests and/or habitats. We went on to discover more on the matter.
A player living in Juiz de Fora, Brazil (elevation: 715 m) reported that he caught 6 Dragonites in the last 7 days. Presumably, Clefairy is very common in Juiz de Fora. Another player also confirmed his suburban findings:
More users have reported seeing the same correlation in the thread comments:
“I can confirm dragonites spawn where clefairys spawn. The only place I’ve seen dragonites is the same place I go to farm clefairys. Here’s the army https://imgur.com/a/KpA0u 2 of these were evolved but the rest all caught at Clefairy area. Doesn’t match your biome type, it’s just a neighborhood but the same type of Pokemon spawn as you say – Barbaric_Emu“
“I’ve noticed that as well. The most popular spot for Dragonites to spawn is Browns Island in Richmond VA. Clefairy spawn there very frequently as well. – BorisLevin“