All -
I believe Joe meant to say "This is the first CO eBird record away from the Front Range and the Arkansas Valley in December." as the eBird map clearly shows many Pine Warbler records on the eastern plains on the year-round map, but change the date range to December and the data is confined to the front range and Ark Valley.
But, Steve's point is extremely valid as eBird is a relatively recent phenomena and there are many observations of notable occurrences that are not reflected in eBird (and many will never make their way to eBird). Additionally, there are recent records of birds which do not appear in eBird as not every birder uses eBird. Heresy indeed ;-)
Good birding,
Kathy Mihm Dunning
Denver