"I want to discuss why in most books illustrations are used instead of photos (this is way common for birders)"

Isn't this mainly due to tradition from Darwin and Audubon?

This is such an awesome project! That's a very interesting subject too, I've wondered about the whole illustration thing before as well. I always assumed it had to do with the variation in plumage from juvenile to adult and male to female, as well as regional variations that would be too difficult to amass a collection of photos for. David Allen Sibley is my hero and his North American bird guide is probably my most well used book.

As for the illustration part of it, my paint of choice for birds is watercolor/gouache, but I hardly consider myself much of a scientific illustrator. You could do a basic ID type illustration (I did a male and female Magnificent Frigatebird for one assignment back in the day). or maybe a simple interaction. I LOVE this one done by Sibley of some crows mobbing a GHO :P http://1.bp.blogspot.com/-2kp4HvuoIuc/Ur9baCN46GI/AAAAAAAADLI/aGP8h7uzgSM/s1600/mobbing%2Bcrows.jpg

I found this - http://studiokayama.com/photography-vs-illustrations-birds/ I hope it helps. and this might also be useful http://books.google.co.uk/books?id=gD8pWkA6TcwC&pg=PA419&lpg=PA419&dq=scientific+bird+illustrations+or+photos&source=bl&ots=as2ufzhAvM&sig=pCY1Z-rX4LPrwSfWg3SKLw4ub9Y&hl=en&sa=X&ei=U5TrUs-CC-2h7Aaf8YGwAQ&ved=0CG4Q6AEwDg

as for the illustration i quite like this idea - http://www.thisiscolossal.com/wp-content/uploads/2012/01/birds-1-600x765.jpg where you do the painting on top of the birds description.

I think it's because ornithologists are technophobic.

You can actually use Wikipedia to find sources! Go to the corresponding Wiki articles you think will help your paper, but then go to the bottom of the page and look through their sources and citations. If not, you can always try using your school's online library database. Often, they have access to peer-reviewed journals and all kinds of research documents.