The bar
graphs which follow represent approximate periods of occurrence of the
regularly occurring species of the state. These approximations are based
on our experience with most species, augmented by published records.
Bear in mind that there is year-to-year variation in both abundance and
arrival and departure times, so that a bar that begins in mid-May, for
example, simply means "usually arrives during the third week of May."
Each month is divided into fourths for this purpose.
Abundances of some
species are quite variable from year to year, and these species are
marked with an asterisk (*). "W" indicates occurrence west of the
Cascades crest. "E" indicates occurrence east of the crest. "WE"
signifies similiar occurrence in both regions.
We have used only three
categories of abundance:
Fairly common to common (thick bar - 
)
Rare to uncommon (thin bar -
)
Very rare or absent"
(blank space)
A thick bar indicates periods when
there is a reasonably good to excellent chance of finding
the species in the appropriate
habitat and region, and a thin bar indicates periods when there is a
fair chance of finding it.
Thus, a thin bar represents either the occurrence of a rare
or hard-to-find species or a period when a common species is
considerably less common.
