There would be tits in the Duchy of Grand Fenwick (if it existed), but not a titmouse. Tufted titmice are members of the same family of birds as the tits of the Old World, including one known as the great tit, and the chickadees of the New World. And while they don’t quite roar, they certainly make themselves heard bellowing their “peter, peter, peter” song from the tops of trees - especially in the spring.
Why the mouse part of the name? Superficial speculation suggests that it’s due to those prominent, black and somewhat beady eyes - resembling the eyes of a mouse. But that would be incorrect. Even though the tufted titmouse is a New World bird, it’s name derives from Old English - “tit” meaning something small and “mose” meaning bird - a small bird. I’m still skeptical because I don’t think there has ever been a lot of Old English spoken in the Americas. The source of the “tufted” part should be obvious from the photos.
The tufted titmouse is a non-migratory bird found widely across the the United States and Canada east of the Rocky Mountains. During the past 50 years, its range has shifted northwards perhaps in response to climate change and changes in habitat. While they will flock up with other similar songbird species like chickadees, they tend to also pair up with a specific mate throughout the year. A group of titmice is called a banditry. Most tufted titmice remain within 100 miles of their birthplace throughout their lifetimes. Like certain contemporary humans, juvenile titmice will often remain with their parents into adulthood even occasionally helping with the rearing of future nestlings. They eat insects and seeds in the wild and appreciate sunflower seeds and suet at feeders. Like chickadees, they will select a single sunflower seed, return to a tree branch, hold the seed with their feet, and pound it open with their sturdy round beaks. Then, they will either eat the meat of the seed or carefully deposit it in a tree crevice for later dining. Tufted titmice nest in cavities created naturally or by woodpeckers or in nest boxes and like to line the nest with hair from animals including raccoons, opossums, mice, squirrels, house pets, and even humans. None of my sources indicate how these hairs are obtained though it is amusing to imagine.
By the way, The Mouse that Roared is an outrageously funny cold war satire adapted as a late-1950s movie starring (in three separate roles) Peter Sellers. The novel, written by Leonard Wibberley, was published in 1955 (the British edition was titled The Wrath of Grapes, which is understandable if you know the plot).