Breeding Codes

Unlike a typical bird list, simply recording a species at a location is not the final step. A bird’s behavior can be recorded and used as evidence of breeding, and the status of that evidence can be grouped into one of four confidence levels:

Observed – non-breeding species (such as a migrating Sanderling) will only ever receive Observed status. This is the default status for each species, and you do not need to select it; a blank breeding code equals an Observed status. In fact, the only actual code that falls under this status is ‘F = Flyover’, which is regularly misused and has special restrictions associated with it. Code F is not used for any flying bird. Instead, code F is only to be used for flying birds that are not using the habitat below them. For example, a Red-tailed Hawk soaring over a field would not be a code ‘F’ because it is foraging over the field, while a Great Blue Heron flying across the highway would be, because it is probably travelling between foraging sites. This code is used by eBird to distinguish birds not using a particular habitat from those using the habitat, so code F should be used sparingly and deliberately. You can read more about code F in the article Using the “Flyover” code in eBird (

Possible – this is the lowest breeding evidence status, and essentially only indicates a bird was present during the breeding season. A block should have no more than 25% Possible codes; most can be upgraded to Probable by making a note of the precise location a bird is singing from and revisiting those sites a week later. If the bird is still singing at that precise location a week or more later, it establishes territoriality and upgrades their status to Probable (code S7). It is important that the recorded location of the bird be precise; a Northern Parula singing at Jug Bay on two different weekends is not precise enough. However, a Northern Parula singing on two different weekends from the small woodlot northeast of the Jug Bay visitor’s center would be. If you have access to one, a handheld GPS is ideal for recording these locations, but a notebook or the comment box in your eBird checklist are also good options.

Probable – most breeding behaviors that do not directly involve nests, eggs, or chicks indicate Probable breeding status. The majority of the species in your block will likely fall under this category, and that is okay. While confirming every species in a block would be great, it is also time consuming. Your atlasing efforts are better spent getting as many species as you can to Probable status, rather than finding nests. The best ways to upgrade birds to Probable status are to return a week after initially finding a singing male and find it singing from the same precise location (code S7) or to find a male-female pair of the same species (code P). Please note that this must be a male-female pair, not just a pair of birds.

Confirmed – confirmed breeding is the highest breeding status, but it can be time consuming to get. Some species are simple; a Canada Goose on a lake with goslings is immediately Confirmed (code FY), but a Common Nighthawk will likely remain Probable without a lot of searching (and potential disturbance). The easiest way to confirm breeding in your block is to watch for species that are carrying food to their chicks (code CF).


Code Behavior Definition
(Blank) Not breeding If a bird is outside of its breeding season or not displaying any behavior indicative of breeding, do not apply a breeding code. Leaving the breeding code blank automatically assigns it ‘Observed’ status, and no further action is required.
F Flying over only This is not necessarily a breeding code, but can be a useful behavioral distinction. Do not use this code for any flying bird. Instead, only use this code when a bird is not using the habitat, as described the article Using the “Flyover” code in eBird (
H In suitable habitat Adult in suitable nesting habitat during its breeding season.
S Singing male Singing male present in suitable nesting habitat during its breeding season.
S7 Singing male present 7+ days Use only if you have observed a singing male at the exact spot (likely to be the same individual) one week or more earlier in the season. Do not use if you have observed a singing male a week earlier elsewhere on the same transect covered by your checklist.
M Multiple (7+) singing males At least 7 singing males present in suitable nesting habitat in the same block on the same day during its breeding season.
P Pair in suitable habitat Male-female pair observed in suitable nesting habitat during their breeding season.
T Territorial defense Permanent territory presumed through defense of breeding territory by fighting or chasing individuals of the same species.
C Courtship, display, or copulation Courtship or copulation observed, including displays and courtship feeding.
N Visiting probable nest site Visiting a probable nest site (primarily hole nesters).
A Agitated behavior Agitated behavior or anxiety calls from an adult. This does not include responses elicited by “pishing” or playing recordings, or mobbing behavior that species engage in year-round (e.g., mobbing an owl).
B Wren/ woodpecker nest building Wrens and woodpeckers may build dummy nests or roost holes and thus nest-building behavior cannot be considered confirmation. Use this code in those cases.
PE Physiological evidence Physiological evidence of nesting, usually a brood patch. This will be used primarily by bird banders.
CN Carrying nesting material Adult carrying nesting materials; nest site not seen.
NB Nest building Nest building at apparent nest site (should not be used for wrens and woodpeckers that build dummy nests; see code “B” for these species).
DD Distraction display Distraction display, including feigning injury.
UN Used nest Nest is present but not active. Use only if you are certain of the species that built the nest. Use 0 to describe the number of birds if none were seen.
ON Occupied nest Occupied nest presumed by parent entering and remaining, exchanging incubation duties, etc.
FL Recently fledged young Recently fledged or downy young observed while still dependent on adults.
CF Carrying food Adult carrying food for young (should not be used for corvids, raptors, terns, and other species that may move many miles from the nest site; often supersedes code “FL”)
FY Feeding young Adult feeding young that have left the nest, but are not yet flying and independent (should not be used with raptors, terns, and other species that may move many miles from the nest site; often supersedes code “FL”).
FS Carrying fecal sac Adult carrying fecal sac.
NE Nest with eggs Nest with eggs.
NY Nest with young Nest with young seen or heard.