By collision, we mean a case where
two or more names would have the same code while applying
the rules. For example, Blackburnian Warbler and
Blackpoll Warbler would both be encoded as
BLAWAR. In that case we devise substitute
codes that still suggest the original names: in this
BKBWAR for Blackburnian
BKPWAR for Blackpoll
We feel very strongly that in all collision cases, the “collision code” must not be used. This allows automatic detection of encoding errors by computer programs. Having a computer detect an error takes a lot less time than catching it in proofreading, assuming you have time to proof it at all.
BLAWAR, and the
other collision forms, are not allowed, even in cases
where one of the names is extremely unlikely to occur.
For example, American Goldfinch collides with an ancient
and obsolete name for Common Goldeneye, “American
Goldeneye.” We disallow the collision code
AMEGOL and require the use of
the substitute codes
AMEGEY. This is a necessity in
the Christmas Bird Count database because so many old
names occur in the early days of that census.
The author's long career working with banding data has convinced him that the four-letter codes devised by the US Fish & Wildlife Service's Bird Banding Lab are highly error-prone. Roughly 100 names are involved in collisions in this system!
Most banders work with a fairly small set of local
species: a bander on the East Coast may encoded Carolina
CAWR, not realizing that
this code is a three-way collision with Cactus Wren and
Canyon Wren. When the code
shows up on a banding sheet, it is not always clear
whether it means Cerulean Warbler or Cedar Waxwing. The
BBL also generally does not use the collision form. In
this case they supply substitute codes
that the appearance of code
on a banding sheet is always an error.
However, they violate this rule in a few cases where one
of the colliding names is highly unlikely to occur on a
banding sheet. For example, because Barnacle Goose is
quite rare, code
BAGO is allowed
for Barrow's Goldeneye, with code
BRNG used for Barnacle Goose. The author
feels that this is risky, since it assumes that everyone
working with bird records knows something about bird