O
Species heard or observed within safe dates, and in suitable breeding habitat.
S
Territorial behavior, including counter singing males
PR
Pair (male and female) of a species interacting non-aggressively and in close proximity to one another, within safe dates, and in suitable breeding habitat.
TE
Singing male or another territorial behaviour at the same location at least twice.
KT
Courtship behavior (aerial displays, courtship feeding) or copulation
OM
Repeatedly visiting probable nest site or nest building by wrens, woodpeckers, kingfisher...
NP
Agitated behavior and/or anxiety calls from an adult, suggesting presence of nearby nest or young (Note: does not include response as a result of 'pishing', tape playback, or presence of predator)
PL
Gravid condition (egg observed in oviduct) or highly vascularized, fluid-filled (edematous) brood patch (Note: code only applies to birds observed in hand and is reserved for experienced birder only)
BU
Nest building observed at nest site (Note: for nest building by wrens, woodpeckers, kingfisher...)
UDA
Distraction display (especially injury feigning, such as broken wing display) or attacking/dive-bombing humans in defense of unobserved nest or young
GNS
Used nest; includes inactive nests, but only those built during atlas period
MŁO
Recently fledged young that are incapable of sustained flight
ZAJ
Occupied nest, but contents not observed; adults entering and remaining for a period of time, then leaving or exchanging duties
POD
Adult carrying food for young within safe date
WYS
Nest with breeding adult observed
PIS
Nest with young seen or heard
Only if not any case above is applicable
NOBS
Not observed despite active search