Breeding Evidence Codes and Categories
Category Description  (see handbook for full description & use suggestions)
OB Code – Observed: not breeding evidence
O Species (male or female) observed within safe dates with no evidence of breeding. Not in suitable nesting habitat.
PO Code – possible breeding evidence
X Species (male or female) observed in suitable nesting habitat during its safe dates.
PR Code – probable breeding evidence
P Pair observed in suitable nesting habitat within safe dates.
S Singing male present (or breeding calls heard) on more than one date, a week or more apart, at the same place. The second observation must be within safe dates.
T Permanent territory presumed through defense of territory (e.g. chasing individuals of the same species).
D Courtship of display between a male and a female or 2 males, including courtship feeding or copulation.
N Visiting probable nest site.
A Agitated behavior or anxiety calls from adult.
B Nest building by wrens or excavation of holes by woodpeckers.
CO Code – confirmed evidence of breeding
CN Bird carrying nesting material (sticks, hay, not feathers), not heading outside of block.
NB Nest building by any species except wrens and woodpeckers.
PE Physiological evidence of breeding, e.g. highly vascularized, edematous brood patch or egg in oviduct based on bird in hand. (For banders.)
DD Distraction display or injury feigning.
UN Used nests or egg shells found. Must be carefully identified, if they are to be accepted.
PY Precocial young. Flightless young of precocial species restricted to the natal area by dependence on adults or limited ability.
FL Recently fledged young (of altricial species) incapable of sustained flight or downy young (of precocial species) restricted to the natal area by dependance on adults or limited mobility.
ON Adults entering or leaving a nest site in circumstances indicating occupied nest. To be used for nests which are too high (e.g. the tops of trees) or enclosed (e.g. chimneys) for the contents to be seen.
CF Adult carrying food for young.
FY Adult carrying food for recently fledged young.
FS Adult carrying fecal sac.
NE Nest with egg(s), undisturbed nest with a bird in incubation posture, or eggshells found below nest.
NY Nest with young seen or heard.