Sierra Nevada Birds Occurrence, Residency & Breeding Status Terms

Occurrence Status Terms

Likelihood the species will be encountered in the proper habitat and time-of-year.

Common – Found in moderate to large numbers, and easily found in appropriate habitat at the right time of year.

Fairly Common – Found in small to moderate numbers, and usually easy to find in appropriate habitat at the right time of year.

Uncommon – Found in small numbers, and usually with some effort in appropriate habitat at the right time of year.

Rare – Occurs annually in very small numbers. Not to be expected on any given day, but may be found with extended effort over the course of the appropriate season(s).

Accidental – Five or fewer records in Stanislaus County and fewer than 3 in the past 10 years.

Irregular – Represents an irruptive species whose numbers are highly variable from year to year. There may be small to even large numbers present in one year, while in another year it may be absent altogether.

Residence Status Terms

Most likely time-of-year that the species is expected to be encountered

Year-round Resident

Winter Visitor (typically October to March)

Summer Visitor (typically May to September)

Spring/Fall Migrants (typically MAR – MAY and AUG – OCT)Vagrant (Can be any time, but more often late fall)

Breeding Status Terms


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 (


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.


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 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).