Well this Question Has much to do with the structure of a Palm Application. I can offer an explanation of this. And mabey this may be something to add to the iziBasic Manual because it does lack in this area.

First lets look into the structure of a windows application (in Basic For example). First you have a Folder in the hard drive that stores the .exe and many other items including Program Data, Updates, Images, Sounds, Video, sub programs and other Interface tools... When you run the application it looks for the folder to find the approiate images to dispaly and correct sub programs(Otherwise known as Resources) to launch.
Low looking on the other end of the spectrum, we find the PalmOS. The Palm has no triditional "Windows Style" file structure. Instead of folders there are PRC files(Otherwise known as a Palm Executible File) But if you look at the PRC File with an Editor like BIRD, You see that a Palm Application is nothing more then a "Folder" The Palm Resources are bundled in the application and all numbered (0001-9999) the Palm Application calls these resources to display images, Play sounds, run sub Programs and store Data. Resource Files have special "extensions". I have listed some of the most common below...

tbmp-----Compare it to a Bitmap in Windows
taib-----Icons there can only be 2
taib 1000---Large Icon
taib 1001---Small Icon
code----Compare to .dll in Windows
code----Can also be executiable Code
code----This is whare PP-lets are stored
tver----Version in Palm Launcher

Now to answer the question as to What is BIRD. BIRD is a resource editor. If you want to create your own custom image to show in your iziBasic application, you would use BIRD to draw a resource with a tbmp extension(i.e. tbmp 100) and use the standard IMAGE Command in izibasic to call the image with that name(refer to the iziBasic Manual for more help on this}.