I think the most commonly noted difference between the female Bullock's
Oriole and Western Tanager would be the bill shape. The tanager has a
thicker blunter appearing bill while the oriole has a more angular sharp
I also think the tanager's dark rounded eye stands out more as it is circled
with the greenish yellow head color and therefore appears quite centered in
the bird's head. The oriole has a hint of an eyeline that tends to give the
eye a more oblong, squinted look giving the impression that the eye is very
close to the bill.
The tanager's tail is also darker than it's back/body color while the
oriole's tail closely matches the back/body color. This is most noticeable
in flying birds.
Habitat can also be a key but in fall migration both birds will be turning up
in odd areas. Vocalizations may also be an aid but doesn't help those of us
who do not hear well. Behavior and feeding can help tip the scales. I have
observed tanager's along the Greenway actively flycatching from perches in
But the biggest key for someone of my limited skill is simply getting a
better look. My 8X binocular was limiting me to birding at 30 yards or less
for the tougher birds. A scope really helps to answer a lot of questions for
me. But the birds have to be cooperative enough to remain posed while I
fumble through the aim and focus drill.
I have to admit also that the strategy of waiting for the male to show up is
one of my weaknesses. However, during migration many species split into
groups based on sex rendering this method to be a very time consuming
practice...plus you need clothing to cover two full seasons.
Your question was phrased to lead me to believe that you have all ready
consulted a field guide. I think this is one of the neatest things about
birding ID. Our questions and failures should spur us to do a little
research to help prepare us for the "nest" time we encounter a bird or
situation. If you have more than one reference, use them all. There is a
lot of info on the Internet and our local library has numerous books
available...including some in the reference section that are for use "in" the
I also hope that some of our more skilled Yakkers can find the time to help
answer your inquiry. The Q & A portion of BirYak is one of my favorite
features. Questions left unanswered discourage me.