Occurrence and Residency Terms

Below is a breakdown of the common terminology used to describe the likelihood of finding a species (Occurrence) and when it is most likely to be found (Residency).

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 Transient (typically MAR – MAY and AUG – OCT)

Vagrant (Can be any time, but more often late fall)