@Christian: [spoiler]Look around Mt. Jemison at night for both bionts.[/spoiler]
Conversely, if you want some up-close-and-personal photos, they each have napping spots where they can be found throughout the day. Although they seem to be restless sleepers, the rover's presence doesn't seem to disturb them.
Once you catch a few images of them at night (which typically will show them at a distance), you'll get a better feel for each of their territories, which in turn will help you narrow down their day locations.
Depending on how many night shots you've taken thus far, it's quite likely that you have already gotten some photos of them at a distance (but perhaps have not identified them as such). The XRI identification algorithm often will not be able to identify them at a distance, but if you look carefully, you can tell what they are.
If you haven't already, you can check some of the images on the Spot the Critter
thread for examples of what they look like at night from afar.
I don't want to spoil this part of the investigation for you (it can be a lot of fun trying to track them down), but if you need more help, let me know.