That conclusion was to use the first letter of the animal's name hidden on each side of any given page and connect it to the corresponding letter opposite it. Like you said, on most pages the intersection point designated a letter, but on some it didn't. We got this sequence: O, A, W, blank, L, G, blank, blank, E, D, E. This combination of letters made little sense.
However, we did find the word EAGLE within the letters, which seemed the only promising idea yet. That left the letters OWD (and three blanks). We noticed that if the D were an L it could spell EAGLE and OWL. The page the D came from (the Lily Pond), does have an L nearby, although I still think the intersecting point is more clearly over the D. Anyway, this is the only solution we found, and I am inclined to think it might be what Adshead intended, for these 4 reasons:
1) Adshead likes birds, a lot
2) There is actually an owl called an Eagle Owl
3) One of Adshead's next books is called the Odd Old Owl and features an owl which might vaguely resemble an eagle owl.
4) There were too many obviously devised clues present for there to be no answer (unless Adshead gave up halfway through creating a puzzle or else has a dark sense of humor, which I doubt), and since I can't find anything else (and I don't want to go crazy looking!), the Eagle Owl answer seems satisfactory.
So, my belief is that Adshead went to all that work to let us know that the Eagle Owl exists and is pretty cool. Plus, it's other name is the Bubo Bubo, which is kinda similar to Dodo. Anyway, thanks for getting us to think. It was an interesting exercise, and I haven't found anyone else on the internet who discovered as much as you did.