 migration is a north-south oriented movement between a breeding and wintering range. But migrations may be very short such as down the slope of a mountain to a lower elevation (vertical migration).
Birds can be conveniently categorized by their migratory or non-migratory status in an area.
a. Residents: those birds that do not enter or leave the state/country/area during migration. Generally, these birds do not move very far during their lifetime.
b. Transients: migrate through in the spring and/or fall but do not nest in the area. Some are pure transients that merely pass through.
c. Winter visitors: are those birds whose breeding range is somewhere north.
d. Summer visitors: are those birds whose winter range is somewhere to the south.
e. Perennial visitors: are those of which individuals are always around.
f. Casual visitors and accidentals (occur unexpectedly). The remaining 6% defy categorization.