| Code | Description |
| OB - O | Observed - no breeding behavior |
| PO - H | Possible - male or female in suitable habitat |
| PO - X | Possible - less than 7 singing males in suitable habitat |
| PR - M | Probable - more than 7 singing males in suitable habitat |
| PR - P | Probable - obvious male and female pair |
| PR - T | Probable - territoriality - chases, defense |
| PR - C | Probable - courtship - copulation, food exchange, displays |
| PR - V | Probable - adult visits probable nest |
| PR - A | Probable - agitated adult |
| PR - N | Probable - nest building by Bald Eagle, House/Marsh Wrens, woodpeckers |
| CO - NB | Confirmed - nest building by all other species |
| CO - DD | Confirmed - distraction display, injury feigning |
| CO - CF | Confirmed - carrying food by adults but young not seen |
| CO - ON | Confirmed - occupied nest by adult |
| CO - NE | Confirmed - nest with eggs |
| CO - NY | Confirmed - nest with young seen or heard |
| CO - FF | Confirmed - feeding recently fledged young by adult |
| CO - FL | Confirmed - recently fledged bird observed |
| CO - FS | Confirmed - fecal sac carried away by adult |
| CO - UN | Confirmed - used nest or eggshells, carefully identified |