GWWA is the 4-letter code for Golden-winged Warbler.
There are two sets of such codes: the USGS BBL (Bird Banding Lab) codes, and the IBP (Institute for Bird Populations) codes. The latter codes are more complete, and are the codes used by eBird to speed up data entry (i.e., you can enter WCSP and it will recognize that is the code for White-crowned Sparrow).
The rules for constructing these codes from bird names are pretty straightforward, so if you'd like to learn these codes I'd recommend learning the rules and memorizing the list of exceptions, and not trying to memorize all the codes individually!
Here are some "cheat sheets" to get you started.
Download in PDF or Word format at
https://people.mbi.ohio-state.edu/hurtado.10/birding.htmlWhile they're for Ohio birds, so list of exceptions isn't complete, the rules are still pretty helpful.
One of these days I'll get around to making a Colorado version! If someone else wants to take a crack at it, I'd be more than happy to format the info into similar "cheet sheets" and make them available online.