Here is the abstract from the May 98 issue of The Condor on the article
"Tricolored Blackbird Itinerant Breeding in California" by William J.
Hamilton III, of UC Davis.

To evaluate the abundance of Tricolored Blackbirds (Agelaius tricolor),
the schedule of breeding throughout the Central Valley of California was
determined in four years (1992-1994, 1997). By the end of April in 1994,
all observed Tricolored Blackbirds were in the immediate vicinity of
active breeding colonies. Only one colony of 600 birds was established in
the Sacramento Valley north of Sacramento County. During late May and
early June, more than 170,000 individuals settled in the Sacramento
Valley, while attendance at colonies in the San Joaquin Valley was
declining. Most breeding birds colonizing the Sacramento Valley in May
and June probably alreay had completed nesting efforts elsewhere. This
suggests that Tricolored Blackbirds are itinerant breeders. Surveys
conducted after initial settlement and before substantial movements from
one breeding area to another occur, have the potential to estiamte
overall numbers. Inclusion of late season breeding colonies in estimates
of overall abundance would result in substantial overestimates of the
global population. Local and regional declnes in the number of breeding
Tricolored Blackbirds of an order of magnitude or more resemble
population collapses but probably are attributable to itinerant breeding.




A couple of comments on historical notes on distribution of Tricoloreds.
Ralph Hoffman in his Birds of the Paciifc States, written around the
1920s, does not acknowledge Tricoloreds outside of California and the
National Geographic Field Guide's map only has birds in California. I'll
check Bent this weekend but my bet is that this movement has occured in
the last twenty years.

In terms of "seeing what you expect", I wonder how much of a factor it is
that observers have not seen Tricoloreds in Oregon and Washington
historically because they just didn't expect to see them. They are
reasonably easy to confuse with Red-wings. I would be very surprised if
this species only recently started to expand its territory.



Jim Rosso
Issaquah, Washington
jrosso at mediaseek.com
jlrosso at msn.com
(425) 392-8440