Audubon apps act weird. Not sure how they work, but it's defiantly different then most apps.
What they seem to do is automatically installs part of the program onto the SD card. If you link it with Link2SD, it seems to take up more internal space then leaving it alone.
I've tried moving the app from the SD to internal and then linking it with Link2SD, but it seems to not gain any more internal memory then if it was the original install on the SD card.
I've found that any of the Audubon just take up space. If the app is 25 megs, you lose that much internal memory.
It stinks because I have 4 or them, but only have 3 installed because they eat so much space. Also right now they are on sale at Google Play for $4.99 ea. There is 2 more I'd buy, but would not fit anyway.
They also do not install on my 7" tablet, which is a bummer. It would be nice since I have 7 Audubon books, and having them on the tablet with a larger screen then my phone would be great.
If you have Link2SD set up correctly, you should be able to free up tons of space by moving your other apps. There is a tutorial in the rooted section that can help get it set up.