Different countries have different committees. Here in the
USA the Americian Ornithological Union (AOU) does the lumping
and splitting. The official list rules are set by the American
Birding Association and the follow the taxonomy layed out by
the AOU. The AOU is fairly conservative and is much less likely
to split taxonomic forms. And there are many taxonomist in
North America who don't agree with or follow the AOU, including
most recently Beadle and Rising who treat Fox Sparrows as four
species and Jeffery Groth who insists there are 8 kinds of
crosbills.

Many European countries have a much more liberal view of species.
The Dutch for example have split large-form and small-form Canada
Geese, many of the gulls, etc.

Joseph Higbee ponders:
>
> I have recently seen on another site where the 'American' Mew Gull (larus
> canus brachyrynchus) and the European Mew or Common Gull (Larus canus) have
> been separated. They are now apparently Common Gull (larus canus) and Mew
> Gull (Larus brachyrynchus). Who makes these decisions and where are they
> recorded? I have searched the web but must be missing something as I have
> turned up no link or reference so far.
>
> Joseph Higbee
> Puyallup,WA.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Half-a-bee, philosophically must ipso-facto half not-be.
But half the bee, has got to bee Vis-a-vis its entity...
d'you see?
But can a bee be said to be or not to be an entire bee
When half the bee is not a bee due to some ancient injury?
-Monty Python

http://www.pacifier.com/~mpatters/bird/bird.html