One resource that might be useful in answering the question of rarest Ohio bird, based on breeding status, is the Partners-In-Flight population estimates database.  http://rmbo.org/pifpopestimates/
The data output can be broken out by Bird Conservation Region (BCR), State or Province, and even BCR within a state or province. 
These population estimates are based on Breeding Bird Survey route data.  So you can view the population estimates for birds that breed in Ohio.  Likewise you can view what percentage of a species' global population breeds in Ohio.  For example it's estimated that 12.6% of the global population of Cerulean Warblers, or about 80,000 individuals out of a total estimate of 600,000 individuals, breeds in Ohio.  Note the colors are data quality ratings, not population trends, where green is the highest quality followed by beige, yellow and so forth. 
Hope this helps,
Casey Tucker                                      
______________________________________________________________________

Ohio-birds mailing list, a service of the Ohio Ornithological Society.
Please consider joining our Society, at www.ohiobirds.org/site/membership.php.
Our thanks to Miami University for hosting this mailing list.


You can join or leave the list, or change your options, at:
listserv.miamioh.edu/scripts/wa.exe?LIST=OHIO-BIRDS
Send questions or comments about the list to: [log in to unmask]