Comments enbedded below.  For orientation, my current position is that
silent Yellow-bellied Flycatchers probably can be identified but not by
all active observers and surely not by everyone who is currently
reporting them.

Matt Hafner wrote:

>Sorry for the delay in responding, I haven't quite had the time to sit down and write a long post.
>
>
>Sean wrote:
>"I also
>find it interesting that the number of Yellow-bellied reports increase in the fall. Of course it could
>be as simple as a different route in fall migration compared to spring migration,
>and because of nesting there is just more birds. I wonder, does anyone else ask the
>same question as this? Is there an answer for this. Did you notice a difference in banding in
>the spring compared to the fall?"
>
>
>A different migration pattern is exactly the case here.  It is quite common for birds to use the central flyway in the spring and use a more easterly route in the fall.  This is case for many circum-gulf migrants.  Personally, I have never worked at a banding station in the spring, but from the information that I know, Yellow-bellied Flycatcher is a more predominant migrant in the fall.  This is the case for several other migrants, Tennessee Warbler, Lincoln's Sparrow, Baird's Sandpiper, Buff-breasted Sandpiper, and many others.  Spring birding in Texas is enjoyable to me because I get to see a ton of birds in the spring that I would never have had the opportunity to see in MD.
>
>
>

But the question is not whether this pattern is possible, it is whether
the different migration routes are in fact used by Yellow-bellied
Flycatchers.  Is there evidence for the change in routes other than the
increased number of sight records in the fall?  If the bulk of the
reported fall sight identifications are not reliable because of the
difficulty of the identification and the overconfidence of some
observers, how do you determine what the migration routes are?  Do
speciment records agree?  Do banding records agree, and are the banding
ids known to be based on reliable measurements?  Of course, the answer
may be that no one has checked the records; not all interesting
questions have yet been studied.

Sight records are the best way to settle most occurrence and even
abundance questions simply because there are so many sight records
reported.  But observer bias is a serious problem with sight records and
has to be considered case by case.  After all, if you are really naive
you can conclude that "the majority of migrants arrive on week-ends."
The Yellow-bellied Flycatcher problem is a lot more subtle, but more
subtle simply means more tricky.

>...
>
>With a group such as empids, the birds are so similar that some should not be identified without good looks.
>
Agreed, with emphasis on "should" as opposed to "can't," and I would
omit the "without good looks."  Moreover, the observer should have
appropriate experience with birds of known identity.  I expect you would
agree with the second assertion.

>However, other than Willow/Alder and Pac-slope/Cordilleran, I have never heard anyone say that silent empids are unidentifiable.
>

That just shows that you are still young  :-).  [Sorry, I couldn't
resist]  Knowledge and fashions change.  There was a long period in
which many observers identified Yellow-bellied Flycatchers and none were
using the current criteria, because the current criteria were not
known.  Some of these observers were quite experienced -- and quite
wrong.  Many people during this period said that Yellow-bellied
Flycatchers could not be identified by sight.  By the criteria of the
time, the skeptics were correct.

>I've spent a long time studying calling migrants and singers on the breeding grounds and feel that many of the differences are consistent enough to use on non-calling birds in the fall.  I will also reiterate that banding birds is a fabulous way increase your experience.
>
>
>
I don't know about Sean, but I am tentatively convinced that a person
who has studied Empids that are identifiable by voice or measurement can
also identify them visually.  I am also convinced that in the process of
learning how, they will make many mistakes, and having those mistakes
corrected by hearing the voice or making the measurements is part of the
learning process.  There are also a lot of people who have not gone
through this process who have convinced themselves incorrectly that they
also can make the identifications.  As a result, sight ids of at least
the more difficult Empics probably should not be used to determine the
status of the species in migration.

It would be very instructive for several people who bird together
regularly and see Empids to make a practice of not discussing the birds
they are looking at until they have made up their minds about the
identification, and then keep track of how often their identifications
agree and how often they disagree.  Agreement would at least indicate
consistent use of criteria.  It would be important to say nothing about
what you see on the bird before comparing ids in order not to give each
other subconscious hints about what you are thinking.  It is also -- to
be fair -- important to realize that the disagreement rate is roughly
twice the error rate if the error rate is small.

>...
>This has been a fun discussion.
>
>

Very much so.  I hope it continues.

>Matt Hafner
>Bel Air, MD
>
>
>


--
Maurice Barnhill
  [Use ReplyTo, not From]
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Department of Physics and Astronomy
University of Delaware
Newark, DE 19716