James Blish 
Midsummer Century [EPUB ebook] 
A Haertel Scholium Book

In the year 25, 000 ADWhen John Martels returned to consciousness he found himself the Delphic Oracle of a world far different from the Twentieth Century. Humanity has risen and fallen three times and was back once again in a semi-primative state.He shared his oracular powers with a mind and a device left over from the last Rebirth, but the real problem was not rebuilding civilization, it was that another genus of creatures had arisen to claim inheritance of the world – the evolved. Strangely intelligent birds, whose priority was the elimination of the world’s former masters.The problem of man versus bird, complicated by the question of John’s personal survival, presents a canvas worthy of the diverse talents of the author of A Case of Conscience and Cities in Flight.