according to the USFW NBS official code book:

Trumpeter Swan = TRUS
Tree Swallow = TRES

The rule is: If two birds have the same 4-code, one picks the next easiest
combination IN BOTH SPECIES that resolves the conflict.


>
>With all this talk about Trumpeter vs Tundra Swans I have noticed that
>everyone seems to use TRSW as the code for the Trumpeter. There is a
>conflict with that code and the Tree Swallow. It is my understanding that
>TRSW is used for the Tree Swallow and TMSW for the Trumpeter Swan.
>
>Hugh Jennings
>Bellevue, WA
>
>

--
*********************************** I was of three minds
* Mike Patterson, Astoria, OR * like a tree
* mpatters at orednet.org * in which there are three blackbirds.
*http://www.pacifier.com/~mpatters* -Wallace Stevens