Birds that frequently travel up tree trunks and peck holes into tree bark to obtain insects and sap. They often drum on hollow branches or metallic surfaces.

https://www.flickr.com/photos/ericbegin/3834792603/
Author: Eric Begin. Creative Commons Attribution-Noncommercial-No Derivative Works 2.0 Generic

• Small woodpecker, common in urban and suburban settings
• Male has red spot on head (female pictured)
• Has high-pitched, squeaky, angry-sounding voice: sharp chirps and a descending "laugh"
• Will come to suet feeders in winter

Remember those old Woody Woodpecker cartoons with the musical laugh? Woody was inspired by an Acorn Woodpecker but modeled in part on the Pileated Woodpecker. Alas, the Pileated doesn't range into Colorado.

https://commons.wikimedia.org/wiki/File:PileatedWoodpeckerOnLog1.jpg
Author: AndrewBrownsword. Public Domain.
Woody Woodpecker image from https://www.polyvore.com/use_woody_woodpecker/thing?id=26992094 used to modify public domain image.

Listen to its high pitched laughing call and compare with Woody Woodpecker, not to mention the red crest.

https://commons.wikimedia.org/wiki/File:Northern_Flicker_%286089627647%29.jpg
Author: Mike's Birds. Creative Commons Attribution-ShareAlike 2.0 Generic

• Formerly considered two species, now one: Western form is “red shafted”, with red under wings; Eastern form is “yellow shafted”
• White rump flashes during flight
• Ants are a significant portion of diet
• Although the Flicker is a woodpecker, it's often seen feeding on the ground, sometimes in the company of robins
• Vocalizations include a resonant, maniacal cackle; a sharp descending "chew"; and a squeaky glass-rubbing sound. Also drums on wood and metal with its bill.