Atlas 1 Breeding Criteria
A set of standardized criteria, similar to those used in most other atlases, was used to establish the breeding status of species recorded during the Atlas 1 period. Species were classified as either "possible," "probable," or "confirmed" breeders by classifying their behavior. A list of the breeding criteria codes and the definitions of the accompanying behaviors that were used during Massachusetts Breeding Bird Atlas 1 follows.
Bird recorded in the breeding season in possible nesting habitat, but no other indication of breeding noted.
S - Singing male present (or breeding calls heard) on more than one date in the same place
T - Bird (or pair) apparently holding territory
D - Courtship and display; or agitated behavior or anxiety calls from adults, suggesting probable presence of nest or young nearby; brood patch on trapped female or cloacal protuberance on trapped male
N - Visiting probable nest site
B - Nest building by wrens and woodpeckers
DD - Distraction display or injury feigning; coition
NB - Nest building by any species except wrens and woodpeckers
UN - Used nest found (use this criterion with caution)
FE - Female with egg in oviduct
FL - Recently fledged young
FS - Adult carrying fecal sac
FY - Adult(s) entering or leaving nest site in circumstance indicating occupied nest
NE - Nest and eggs or bird setting and not disturbed or eggshells found away from nest
NY - Nest with young or downy young of waterfowl, quail, waders, etc.