Check the boxes

Can you find a common theme shared by these three photo mosaics?

Here's the first one:

 

Any ideas yet?  

Here's the second one: 

 

Need a hint?  Consider the first letter for each organism, starting in the upper left corner and reading like a book.

The third mosaic:

 

I know this is tricky.  And the theme is?

For the first mosaic: Veliger, Otter, Tern, Echinoderm

For the second mosaic: Vulture, Octopus, Trifolium, Eagle

For the third mosaic: Vermetid, Owl, Toad, Egregia 

Thanks so much for playing.  Don't miss your chance to use your voice in the elections on Tuesday!