The early bird tome is a book received after completing The Elder Kiln in the 2 weeks following its release. Reading it provides 50,000 Magic, 30,000 Agility, and 100,000 experience in the combat skill of your choice (as long as the skill is over 75).
Trivia[]
The examine text mentions rubbing it, which is usually for the case of xp lamps rather than tomes.