Short answers, pulled from the story.
The "chick-a-dee-dee" call of North American chickadees in the genus Poecile serves as both an alarm and a rallying signal to mob a predator. The number of "dee" syllables at the end of the call increases with the level of danger the predator poses, giving flock members a graded warning.
The family Paridae contains 62 species in 13 genera, according to the AviList checklist. They range across most of Europe, Asia, North America, and Africa.
The European blue tit holds the record, having laid as many as 19 eggs in a single clutch under favorable conditions. Typical clutch sizes for the blue tit run from 10 to 14 eggs.
Tits rank among the most intelligent birds after corvids and parrots. Studies on the Japanese tit (Parus cinereus) showed that their calls encode specific messages whose meaning changes with order, a structure researchers have compared to syntax and grammar. Tits have also been shown to form mental images in response to calls signaling a snake's presence, a cognitive ability previously documented only in humans.
The name titmouse is recorded from the 14th century, combining the Old English bird name mase (related to Proto-Germanic maison, Dutch mees, and German Meise) with tit, meaning something small. The spelling shifted from titmose to titmouse during the 16th century under the influence of the word mouse.
Tits settled North America twice, probably during the Early-Mid Pliocene. The ancestors of the genus Baeolophus arrived first, and the chickadees came somewhat later.