Where to Find and Catch Decidueye
From Pokemon Go Wiki
Decidueye are found and captured in Nest and Habitat locations.
Nests
Decidueye Nests are locations that consistently spawn Decidueye.
Habitats
Decidueye Habitats are spawn locations where Decidueye is likely to be encountered, but not guaranteed the way a Nest is.
Additional Tips and Information
Best Nests
If you know a really good nest or any of the nests above is really good, list them here: