The Dark Half, by Stephen King

At age 11, two things happened to Thad Beaumont. He received praise for a story that he entered in a contest, and, after terrible headaches & seizures, had something removed from his brain that the doctors called a tumor. Now he is in his late 30s, married, father of twin babies & author of several books. His more successful books were written under the pen name George Stark. In 1989 he decides to bury the pen name & go back to writing as himself. Soon he becomes suspect in several murders, where his fingerprints are found. Thad knows he didn't do it, but has a good idea who it is: George Stark, a man who never was. George calls Thad on the telephone & demands that he begins writing another George Stark novel or he & his family will not survive. At first, Thad is very reluctant to do so, but as the story goes on & the deadline is reached, he agrees to meet with George to start a new book. George convinces him of this by kidnapping his family & holding them at Thad's lake cottage. By now he has discovered that George is some part of his own twin, who died before Thad was born & was removed from his brain during the operation when he was 11. Throughout the story, thousands of sparrows land near & around Thad's location whenever there is trouble. These sparrows are now surrounding the lake cottage as George & Thad are inside writing. George doesn't know about the sparrows, but Thad does. He realizes that he is the commander of them. They fly into the windows by the thousands, smashing into the house, flying up to Thad's office where he & George are, while Thad's wife, kids & the local sheriff wait downstairs. The sparrows peck at George until he's not much more than a skeleton, then carry him off to the end of the earth, leaving the family safe behind.