Great but flawed resourced
While its great to have access to the quality information available in the app, the presentation needs improvement and falls far short of the paper book (while it should be the other way around). The main shortcoming Ive run into is that when trying to browse in order to identify a bird, the index view shows only one variation. For example, I saw a dark-eyed junco in Colorado. The main image for that bird shows a variation completely unlike the pink-sided variation I was seeing, leaving me confused until later I used the book, which displays all the variations on the page. Identification was the easy and immediate. Also the images are way too small when searching through the taxonomic or alphabetical indexes. My other complaint is that the list feature is tragically primitive. No location support, so you have to clumsily label places instead. Im glad I have the resource available on my phone and iPad, but it could/should be so much better and more useful.
Sintactic about
The Sibley eGuide, v1.8