Sources:
  1. Utah Birds: A Revised Checklist by Behle, Sorensen & White  [sightings before 1985]
  2. Great Basin Naturalist Memoirs, #1 (1976 BYU Press)  [sightings before 1976]
  3. Utah Birds, Guide, Check-list and Occurrence Charts by William H. Behle & Michael L. Perry  [sightings before 1975]
  4. The records of the Utah chapter of the Union of Field Ornithologist  [sightings between 1980 and 1987]
  5. Christmas Bird Count records after 1972 have been checked. [sightings after 1972]
  6. The reports of the Utah Bird Records Committee of the Utah Ornithological Society   [mainly sightings after 1984]
  7. Records reviewed by the Utah Bird Records Committee [sightings since the last Records Committee report]
      

"Documented" and "unconfirmed" sightings:

"Documented sightings" are those that have been accepted by the Utah Bird Records Committee and have come from the sources listed above. The "unconfirmed sightings" are those from hotline reports, Christmas Bird Count reports, records received by the Records Committee by not reviewed and from records that were not accepted by the Records Committee, but that may have been a sighting of that species.
The "Comprehensive Sightings List" contains both types of sightings and indicates the "documented sightings" with the symbol  "⌂ ."
  

Abbreviations:
   UOS - Utah Ornithological Society
   UFO - Utah Field Ornithologists
   CBC - Christmas Bird Count (sponsored by the Audubon Society)
  

Birds seen in Utah that are not on the Utah Checklist:

There are several sightings of bird species that do not appear on the official checklist of the birds of Utah.  Here is a list of those birds with some comment:  

New Birds on Utah Checklist:

See "Recent changes in the Review Species List." Look at the "additions" sections to see the bird species recently added to the state checklist.

There's also a list of "First State Records", which has links to the first accepted sight records for Utah.

Gunnison Sage-Grouse:  "There is a small population in the Monticello area (~100 birds) that have been studied for a number of years by Utah Division of Wildlife biologists and others. Clait Braun, who did the taxonomic work on the Gunnison's, talked about the two species and the proposed changes (now adopted by the AOU) at a Utah Wildlife Society meeting 3-4 years ago. Most of the Gunnison grouse are in Colorado and Colorado has developed several management plans to protect the grouse and hopefully prevent it from being listed. I haven't checked but I suspect there are a number of specimens of Gunnison grouse in the collections at U of U, USU, and BYU."  ~ Steve Hedges  [year 2000]

Cackling Goose:  As of 1994, a new species, Cackling Goose has been split off of the Canada Goose species.  Here's an article on "The New Goose" by Mark Stackhouse.