Since it wasn't seen, how can European Starling be eliminated. Ash-throated Flycatchers are not regular in the Denver area anytime, and the earliest migrants in Colorado don't appear until April, and usually not very early April.
Any very early migrants, really need to be seen, as Starlings are making lots of noises right now and imitate many species, throughout the year.
Brandon Percival
Pueblo West, CO