Breeding and Behavior Codes provide a way for birders to document the breeding activities of birds around the world, providing crucial information for research and conservation globally. Our goal is to collect information about the timing and locations of bird breeding behavior on a year-round and worldwide basis.


Piping Plover by Kyle Tansley/Macaulay Library the Cornell Lab (ML162730121)


Quick Links

Entering Breeding and Behavior Codes

Breeding and Behavior Code Definitions

Breeding Behavior Code Reinterpretation

Breeding and Behavior Code FAQ


Entering Breeding and Behavior Codes

To enter these codes on eBird Mobile, tap a species name to pull up the “Observation Details” menu, tap “Breeding Code” to access the menu, and then choose the highest-ranking code from the list (the lower down, the higher-ranking). 


You can also add these codes from the eBird website as you enter data on Step 3 or by clicking the “Edit Species” button. Once you’ve found the species you want to enter a code for, click the "Add Details" button next to the species in the checklist, select "Breeding Code" from the tabs that appear, and then choose the highest-ranking code that you observed for that species on this checklist. 


Note: you can access your collected breeding code information from each checklist's observation report and through "download my data.” Using the download option allows you to see all breeding records that you have submitted to date.


Breeding and Behavior Code Definitions

These are the definitions for our breeding codes and how they should be used. These codes generally describe behaviors that signify breeding. Specific projects (e.g., eBird Atlases) may suggest using codes only during certain times of year or situations. Please refer to specific project guidelines if you are participating in that project. If you are unsure which code to use, do not record a code but put notes in your species comments.


  • NY Nest with Young (Confirmed) -- Nest with young seen or heard.
  • NE Nest with Eggs (Confirmed) -- Nest with eggs.
  • FS Carrying Fecal Sac (Confirmed) -- Adult carrying fecal sac.
  • FY Feeding Young (Confirmed) -- Adult feeding young that have left the nest, but are not yet flying and independent (for some projects should not be used with raptors, terns, and other species that may move many miles from the nest site; often supersedes FL).
  • CF Carrying Food (Confirmed) -- Adult carrying food for young (for some projects should not be used for corvids, raptors, terns, and certain other species that regularly carry food for courtship or other purposes).
  • FL Recently Fledged Young (Confirmed) -- Recently fledged or downy young observed while still dependent upon adults.
  • ON Occupied Nest (Confirmed) -- Occupied nest presumed by parent entering and remaining, exchanging incubation duties, etc.
  • UN Used Nest (enter 0 if no birds seen) (Confirmed) -- Nest is present, but not active. Use only if you are certain of the species that built the nest.
  • DD Distraction Display (Confirmed) -- Distraction display, including feigning injury.
  • NB Nest Building (Confirmed/Probable) --  Nest building at apparent nest site (should not be used for certain wrens, and other species that build dummy nests; see code "B" below for these species).
  • CN Carrying Nesting Material (Confirmed/Probable) -- Adult carrying nesting material; nest site not seen.
  • PE Physiological Evidence (Probable) -- Physiological evidence of nesting, usually a brood patch. This will be used only very rarely.
  • B Wren/Woodpecker Nest Building (Probable) -- Some species, including certain wrens (e.g., Marsh Wren), woodpeckers, and certain other cavity nesters (e.g., barbets) may build dummy nests and thus nest building activity cannot be considered confirmation. Use this category in those cases.
  • A Agitated Behavior (Probable) -- Agitated behavior or anxiety calls from an adult. This excludes responses elicited by "pishing", playing recordings, or mobbing behavior that species engage in year-round (for instance, mobbing an owl).
  • N Visiting Probable Nest Site (Probable) -- Visiting repeatedly probable nest site (primarily hole nesters).
  • C Courtship, Display or Copulation (Probable) -- Courtship or copulation observed, including displays and courtship feeding.
  • T Territorial Defense (Probable) -- Permanent territory presumed through defense of breeding territory by fighting or chasing individuals of same species.
  • P Pair in Suitable Habitat (Probable) -- Pair observed in suitable breeding habitat (for some projects only during breeding season).
  • M Multiple (7+) Singing Birds (Probable) -- At least 7 singing birds present in suitable nesting habitat (for some projects only during breeding season).
  • S7 Singing Bird Present 7+ Days (Probable) -- Use only if you have observed a singing bird at the same spot (not elsewhere) one week or more earlier in the season. 
  • S Singing Bird (Possible) -- Singing bird present in suitable nesting habitat (for some projects only during  breeding season).
  • H In Appropriate Habitat (Possible) -- Adult in suitable nesting habitat during its breeding season. 
  • F Flyover (Observed) -- Flying over only -- Use it only when all individuals are seen as flyovers; do not use it if just one bird stops or is located feeding on the ground or in vegetation. Raptors, swallows, and swifts that are flying overhead and not obvious migrants are not flyovers, since these birds are often using the habitat in ways not obvious to observers on the ground. This restriction depends upon the judgment of the observer, so when in doubt, do not use this code. 

Breeding Behavior Code Reinterpretation

When perusing breeding codes in eBird Breeding Bird Atlases, you occasionally may notice that a breeding code has been crossed out and replaced with a different breeding evidence level (Observed, Possible, Probable, or Confirmed). This is a reinterpreted breeding code. Breeding codes are reinterpreted when the behavior you reported has a different meaning than the default breeding evidence level.



If you have doubts about how to report a breeding behavior, add detailed written comments to your observation and include media if possible. This makes it much easier for the Atlas coordinator to decide how the code should be interpreted.


If you have a question about the reinterpretation or think something may have been reinterpreted in error, please contact your local eBird reviewer or Atlas coordinator (click here for a list of eBird Atlas portals). 


Here are a few examples of when this may happen:


Example 1 - Migratory songbirds singing in areas where they don’t typically breed

Say you're out birding on a nice May day somewhere south of the boreal forest and you hear a Cape May Warbler singing. You report the bird as "S Singing Bird (Possible)" even though it’s just a migrant at your location. So the behavior of singing is correct, but the interpretation is not that it is a "Possible" breeder. In eBird, this would then be reinterpreted as "S Singing Bird (Observed)", since the interpretation of the singing behavior is only that it was "Observed" at the location.


Example 2 - Raptors and terns feeding young away from the nest

It's late July and you find a group of Caspian Terns at your favorite shorebird spot. One of the adult Caspian Terns is feeding a younger bird - how cool! You report  "FY Feeding Young (Confirmed)". Normally this would be another Confirmed species for your Atlas totals. However, terns will often feed young many miles—sometimes many tens of miles—from the actual nesting site. So although the behavior was correctly reported as feeding young, it is not interpreted as Confirmed breeding at this site. Depending on the specific scenario and the likelihood of breeding in the block, it could be re-interpreted as a "Possible" breeder or as “Observed” instead.


Example 3 - Waterfowl performing courtship during non-breeding months

It’s late July again, but this time you’re in southern Argentina where it’s the middle of winter. While scoping an open lake you see a flock of Red Shoveler. Several birds are being unusually noisy, bobbing their heads up and down at each other - an obvious courtship display! You report “C Courtship, Display, or Copulation (Probable)”. However, even though Red Shovelers start forming pairs in mid-winter, it’s much too early for breeding. These shovelers may migrate to a different region to actually breed. So the courtship display is later re-interpreted as “Observed” instead of “Probable”. 


Why reinterpret breeding codes? 

Reinterpretation of breeding codes allows for the fact that the same behavior might have different meanings for different species or at different times of the year. This allows eBird Atlas coordinators to interpret the meaning of behaviors at larger scales throughout the dataset in a consistent, transparent manner. If you are taking part in an eBird Atlas, please follow the specific guidelines of that project for when to report breeding behavior codes.


How is this different from eBird review? 

Elsewhere in eBird, the data review process focuses on whether observations are publicly visible on species maps, scientific outputs, Explore pages, etc. Breeding code reinterpretation maintains the behavior you reported but allows the meaning of that behavior to be tailored for the specific Atlas you are contributing to - increasing its value to the project. When a breeding code is reinterpreted, the post-reinterpretation category is displayed on public Atlas species maps.


Breeding behavior code reinterpretation can only be done by an eBird Atlas coordinator. This functionality is currently limited to active eBird Atlases and only breeding codes are affected. The species, counts, and effort information on your checklist can never be changed by anyone but you.


Breeding and Behavior Code FAQ (Frequently Asked Questions)

If I see a nest of birds, should I include the count of the adults and the young in my eBird submission?

Yes! Any bird that has hatched from an egg should be counted in your eBird submission.


If I see a nest with eggs, should I count the eggs towards the count of the species in my eBird submission?

No! Eggs are not yet birds, so please do not count them. We encourage you to enter a species comment and upload a photo of the nest/eggs, but do not add them to the tally for the species. 


If I see baby grouse, baby geese, or baby shorebirds that cannot yet fly, what code should I use?

Use "FL". They are fledged in the sense that they have left the nest, which is typical for the young of “precocial” species. "FL" should be used until young birds become independent of their parents, since it is safe to assume that they are near the nesting site until that point.


How do I know when to use P and H?

These categories should be used whenever one or more birds are observed in appropriate breeding habitat and within breeding range. A Marsh Wren in a dry grass field would not qualify, nor would a Sedge Wren on its wintering grounds on the Texas coast, but a Pine Warbler in pine trees within its breeding range would. If you are unsure, do not record a code but put notes in your species comments.