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Breeding Bird Atlas Breeding Codes

The New York State Breeding Bird Atlas uses three categories to record breeding behavior: Possible (PO), Probable (PR), and Confirmed (CO). Within each of these categories are Breeding Codes that describe the breeding behavior. These codes are listed in order of increasing certainty.

Breeding Behavior Categories and Breeding Codes
Breeding Behavior Breeding Code Description
Possible
Breeding
(PO)
X Species observed in possible nesting habitat, but no other indication of breeding noted; singing male(s) present (or breeding calls heard) in breeding season.
Probable
Breeding
(PR)
S Singing male present (or breeding calls heard).
P Pair observed in suitable habitat in breeding season.
T Bird (or pair) apparently holding territory. In addition to territorial singing, chasing of other individuals of same species often marks a territory.
D Courtship and display, agitated behavior or anxiety calls from adults suggesting probable presence nearby of a nest or young; well-developed brood-patch or cloacal protuberance on trapped adult. Includes copulation.
N Visiting probable nest site. Nest building by wrens and woodpeckers. Wrens may build many nests. Woodpeckers, although they usually drill only one nest cavity, also drill holes just for roosting.
B Nest building or excavation of a nest hole.
Confirmed
Breeding
(CO)
DD Distraction display or injury-feigning. Agitated behavior and/or anxiety calls are
Probable-D.
UN Used nest found. Caution: These must be carefully identified if they are to be counted as evidence. Some nests (e.g. Baltimore Oriole) are persistent and very characteristic. Most are difficult to identify correctly.
FE Female with egg in the oviduct (by bird bander).
FL Recently fledged young (including downy young of precocious species - waterfowl, shorebirds). This code should be used with caution for species such as blackbirds and swallows, which may move some distance soon after fledging. Recently fledged passerines are still dependent on their parents and are fed by them.
ON Adult(s) entering or leaving nest site in circumstances indicating occupied nest. NOT generally used for open nesting birds. It should be used for hole nesters only when a bird enters a hole and remains inside, makes a change-over at a hole, or leaves a hole after having been inside for some time. If you simply see a bird fly into or out of a bush or tree, and do not find a nest, the correct code would be Probable-N.
FS Adult carrying fecal sac.
FY Adult(s) with food for young. Some birds (gulls, terns, and raptors) continue to feed their young long after they are fledged, and even after they have moved considerable distances. Also, some birds (e.g. terns) may carry food over long distances to their young in a neighboring block. Be especially careful on the edge of a block. Care should be taken to avoid confusion with courtship feeding (Probable-D).
NE Identifiable nest and eggs, bird setting on nest or egg, identifiable eggshells found beneath nest, or identifiable dead nestling(s). If you find a cowbird egg in a nest, it is NE for Cowbird, and NE for the identified nest's owner.
NY Nest with young. If you find a young cowbird with other young, it is NY for cowbird and NY for identified nest owner.

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