Hi Jonathan:

Interesting question ... that is, ignoring the range, but just looking at 
the field mark differences between the two. The BNA-online account was not 
all that useful. Below are excerpts from the "Identification" sections of 
the two species accounts from the following ...

         Jaramillo, Alvaro and Peter Burke, 1999. The New World Blackbirds. 
Princeton University Press.

Epaulet color, alone, is therefore not sufficient for identification. One 
needs to consider the size and shape of the bill, wings, and tail, as well 
a vocalizations.

 From New World Blackbirds ... (capitalized highlights added) ...

Red-winged Blackbird:
In North America, adult male Red-winged Blackbirds are basically 
unmistakable, outside of California. No other bird is black with red and 
yellowish shoulders. The closely related Tricolored Blackbird (62) poses a 
problem in California, Oregon, N Mexico and surrounding areas. Tricolored 
Blackbird differs in shape from 'Redwing', having a longer, thinner bill as 
well as a more squared-off tail. The rnain feature to look for is the white 
median coverts of Tricolored Blackbirds, rather than buff or yellow; note 
that fresh fall Tricolored Blackbirds may show a buff tone to the epaulet 
borders and that WORN RED-WINGED BLACKBIRDS MAY SHOW WHITE EPAULET BORDERS. 
However, fresh Tricolored Blackbirds have cold greyish-buff feather edges 
to the body plumage, unlike the cinnamon, warm buff, or chestnut colors of 
'Redwings'. The black plumage lacks a noticeable gloss on Red-winged 
Blackbird, but has a faint bluish gloss on Tricolored, which can be obvious 
in good light.

Tricolored Blackbird:
The identification of this species is complicated due to the overall 
similarity of this species to Red-winged Blackbird, in addition to the 
variability of that species. Tricolored Blackbird may be found, often in 
the same flock, with typical Red-winged Blackbirds and 'Bicolored' 
Red-winged Blackbirds (61X). Male Tricolored Blackbird is more similar to 
males of typical Red-winged Blackbird, while females are similar to female 
'Bicolored Blackbirds'. In general, Tricolored Blackbirds are 
slimmer-billed than their sympatric 'redwing' forms and tend to show more 
square-tipped tails. In addition, the wing formula differs, with Tricolored 
Blackbirds having a slightly more pointed wing (Figure 61.1), but this is 
difficult to assess in the field.
The males are more glossy than male Redwinged/'Bicolored' Blackbirds, but 
this is only obvious in direct comparison. ... TYPICAL RED-WINGED 
BLACKBIRDS WITH THEIR BUFFY YELLOW MEDIAN COVERTS MAY CAUSE AN 
IDENTIFICATION PROBLEM EARLY IN FALL WHEN TRICOLORED BLACKBIRD'S MEDIAN 
COVERTS ARE LIGHT BUFF. Note that on Tricolored Blackbird, the red of the 
epaulet is more intense, the median coverts are buff without a yellow tone 
and the upperpart fringing is greybrown rather than rusty-brown.


Also, FYI  ...

         http://www.sdnhm.org/research/birdatlas/focus/blkbirds.html

         http://pick4.pick.uga.edu/mp/20q?search=Agelaius+tricolor&guide=Birds

         http://audubon2.org/webapp/watchlist/viewSpecies.jsp?id=205


Hope this helps! Maybe someone that has lived in the west can provide 
addition information.

Phil


At 16:40 03/04/2006, Jonathan Balcombe wrote:
>Dear birders,
>How much variation does one see in the yellow epaulette of Red-winged
>blackbirds? I read in my guides that it can appear buffy. The one I saw
>today behind my house (through a spotting scope from the upstairs window)
>looked clearly white, esp compared to the yellow one on the male next to
>him.
>
>I'm not suggesting that there is a tricolored blackbird in Maryland! But I
>would appreciate any input from others who may have experience/knowledge
>with the subtle differences btw RWBBs and TBBs.

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Phil Davis      Davidsonville, Maryland     USA
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