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Streptopelia decaocto
Has a white, long tail, with black/brown feathers surrounding the rest of the body.
Likes warm temperatures, and subtropic Asia, and lives in all places of America.
Those are doves. White-Tailed Hawks do not really go so far as Utah. I am not sure which species, but you can look at this list to help you out: https://en.wikipedia.org/wiki/List_of_bi...
Please fill out the habitat section with a description of the habitat you spotted these in, not the general habitat of the overall species. Hopefully someone else can help narrow it down to species. Good luck!