I like to make regular use of the Colorado Breeding Bird Atlas II text. One plus for eBird is that it is readily at hand for anyone, and (as far as the mapped distributions go) it has much more data and is more current. For the Red-bellied, both atlas and eBird sort of show the same thing (RBWO occur mostly in the NE part of Colorado, but eBird gives a richer picture, especially in showing the general river corridor patterns
Colorado Breeding Bird Atlas II
eBird species map for the nesting months of May, June and July
David Suddjian
Littleton