What is Titmice?

At the beginning of the novel there are several birds, called Titmice, that are banging themselves against the window trying to get into the cabin. Trond is confounded at what they are trying to get from him. These birds represent memories from his past that have been kept at bay for long enough, and with his move to the cabin, are not going to be ignored. But like birds, his memories are fragile and if he doesn't deal with them soon, it will be too late.