The birding codes used on this web site describe how likely an experienced birder (one who is familiar with the local birds, by sound as well as by sight) is to find a particular species during a morning of serious birding, in the proper habitat. This is not the same thing as describing how common a bird is.
The birding codes used on this web site are based on the codes developed by David Styer and Ned Keller for the Cincinnati Nature Center’s checklist. Codes A through D are the ones used there; Keller has added Code E for the less frequent, but still regular, species. The codes are:
A. Easy to find; should find on over 90% of your trips.
B. Usually find; should find on over 50% of your trips.
C. Usually miss; should find on under 50% of your trips.
D. Hard to find; should find on under 10% of your trips.
E. Very hard to find; may not be present at all at this time in some years, but has occurred often enough to form a pattern.
We derived these codes by examining the database for reports of each species for each quarter-month of the year, using only what appeared to be (at least nearly) complete trip lists, rather than isolated sightings. For each quarter-month, we then computed the percentage of trips on which each species was found. The actual percentages which we found were much lower than the 90/50/10 percent categories, since many field trips did not go to the right habitat. For example, a field trip to the Oxbow in mid-March would not report any forest birds.
Although there were some surprises, the results were about what we would have expected for most species. We made some minor adjustments to the codes where data were sparse, but for the most part the codes that you see here match our results quite closely.
However, it is important to remember that any attempt to represent how easy it is to find a bird, throughout the year, with a single code, has to be a gross oversimplification.
Also, be aware that this checklist was last updated nearly a decade ago, and could stand to be revised.