[CT Birds] The role of probability in bird identification

David.F.Provencher at dom.com David.F.Provencher at dom.com
Fri Jan 9 09:56:34 EST 2009

Every time a birder is in the field, he or she is using probability in
identifying some of the birds seen. The degree of probability is what
really counts. To use the example Mark mentioned, if a flock of 500
American Robins passes over and we call them 500 American Robins without
identifying each and every one, we are probably correct. The probability
that a Fieldfare was mixed in is quite small but it is not zero, there
might have been one. Even less probable would be a Carolina Chickadee among
the 200 Black-capped Chickadees reported in a Christmas count area in CT.
So even though this identification requires close scrutiny, it is so
improbable to be an issue here that the question virtually never raised. So
when does probability no longer help us? Well that can't really be defined
in absolute mathematical terms, it is an admittedly nebulous point that is
essentially defined by each birder based on his/her personality,
experience, and beliefs. In my opinion, an example of poor reliance on
probability would be finding a small empidonax flycatcher in CT in December
and calling it a Least based on the fact that they breed here. In fact it
would probably, indeed almost certainly, not be a Least Flycatcher based on
historical data.

I do know this, being a member of the Avian Record Committee, if you submit
a report of a Western Meadowlark in CT , the committee will essentially
require you prove it isn't an Eastern. This will be true no matter what
time of year the sighting occurs. As I said, it is a question of
probability, or another case of Occam's Razor. Whenever trying to identify
a rare bird, one must first assume it probably is a commonly found species
and then try to acquire adequate proof it is not.


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