I've been to The Gambia six times (going again later this year) and Senegal twice. I took my first copy of this book with me on the first trip and realised immediately what a boon it was, being able to quickly check IDs, behavourial habits, etc..
If ever there were a Bible of Gambian birding, this would be it.
Have to say, it got a bit heavy to carry all day so I ended up cheating a bit! I carefully separated the plates (images) and basic info section at the front from the more detailed information in the back half of the hardback book, created a new soft cover (laminated with Transpaseal) for that plates section and now just carry that out in the field, with the rest of the volume back at my accommodation to use more thoroughly at the end of the day.
Our guides always have their own copies with them anyway, so we often have a few minutes of perusing, heads together, just to confirm we saw what we thought we saw!
I do have a pristine copy on my bookshelf at home but my now rather dog-eared travel copy has been the best few pounds I've spent on holiday preparation and has made the difference between absolute involved enjoyment and vague wondering what that was flying past...