Sean and others,

I am curious as to where you heard that they were impossible to differeniate because that is certainly something I have not heard before.  I think this is a case of where using only one field mark for identification can be a major pitfall.  The yellow throat often cited as a feature of YB Fly can also be seen on young Acadians, but never to the same extent in my opinion.  Also, YB and Acadian are close to the same overall color, which is very green.  These similar features can lead to confusion, but the structure of these birds is quite different.  YB Fly is more similar to Least Flycatcher in structure, with a small build, short primary extension, and large rounded head.  Acadian is more elongated, with a long primary extension, and head that appears the right size for the body.

Of course this is not the full story and some birds can not be identified without great looks.  I recommend studying Kaufmann's Advanced Birding book for more detail and birding often in August, when many empids are moving through.  I also learned a lot from banding at Chino Farms seeing empids of all ages.


Matt Hafner
Bel Air, MD