A 5 pound yorkie outside by itself is a very bad idea! Sadly, it may take Darwin to show them.
https://www.google.com/#q=Brighton,%20CO%20weather
Ritght now, temps aren't too bad but CO is know for extreme temps seasonally.
"Prairie dogs, 1-3 pounds, are an important food source to predatory birds such as Ferruginous Hawk and Golden Eagle (Giovanni et al. 2007)."
That's a quote from a report from just north of you a bit. Page 15
http://rmbo.org/v3/Portals/0/Documen...l%20Report.pdf
Obviously the point is, you have raptors in the immediate or close proximity. It's only a matter of when he'll be a bird meal, not if.