Daphne du Maurier:

It is a very cold winter and there are many more birds around than usual. Nat is afraid, for the birds keep coming in their thousands and they are hungry. They want to kill. "Penguin Readers" is a series of simplified novels, film novelizations and original titles that introduce students at all levels to the pleasures of reading in English. Originally designed for teaching English as a foreign language, the series' combination of high interest level and low reading age makes it suitable for both English-speaking teenagers with limited reading skills and students of English as a second language.