You can mount the iPod as an external hard drive, which allows you to keep any data you like on it. Here's how you do it:
1. Connect your iPod.
2. If it appears on the desktop, then you can just drag any files you want to it like a hard disk.
3. If it doesn't appear on the desktop, open iTunes and select the iPod in the left sidebar.
4. Click the button with the picture of an iPod at the lower right corner of the iTunes window.
5. In the dialog box, check the box labeled "Enable FireWire Disk Use."
6. Your iPod should now show up on the desktop. Drag whatever files you want to it.
7. When you're done, drag the iPod to the trash (which will become an "eject" icon) and disconnect it.
If, however, you want to store data on the iPod that you can view on the screen whenever you want, you'll need to use a special program to make a special vCard. A vCard is just the type of file used to store contact information on the iPod, for viewing with the Contact list included in the latest versions of the iPod software.
There are a couple different ones on VersionTracker:
PodWriter: <a href="http://www.versiontracker.com/moreinfo.fcgi?id=14121&db=mac
PodNotes: <a href="http://www.versiontracker.com/moreinfo.fcgi?id=14156&db=mac
PodNews: <a href="http://www.versiontracker.com/moreinfo.fcgi?id=14261&db=mac
Some have extra features. PodNews, for example, will allow you to download news from hundreds of news websites for later viewing.
I think the limit is 1000 characters for a text entry, so you'll have to have a separate entry for each species.