Short answers, pulled from the story.
A finch is a small to medium-sized passerine bird in the family Fringillidae, known for stout conical bills adapted for eating seeds and nuts and often colourful plumage. The family contains more than two hundred species divided into fifty genera, including canaries, siskins, redpolls, serins, grosbeaks, euphonias, and the Hawaiian honeycreepers.
Finches and canaries were used in the coal mining industry in the UK, US, and Canada to detect carbon monoxide. The practice ran from the eighteenth to the twentieth century and ceased in the UK in 1986.
No, Darwin's finches of the Galapagos islands are not true finches. They are now considered members of the tanager family, Thraupidae, rather than the finch family Fringillidae.
The family Fringillidae contains 235 species divided into 50 genera and three subfamilies. The subfamilies are the Fringillinae with the chaffinches, the Carduelinae with 183 species across 49 genera, and the Euphoniinae with the Euphonia and Chlorophonia.
The largest finch is probably the collared grosbeak, Mycerobas affinis, at up to 24 centimetres and 83 grams. Among the smallest classical true finches are the Andean siskin at as little as 9.5 centimetres and the lesser goldfinch at as little as 8 grams.
The name Fringillidae was introduced in 1819 by the English zoologist William Elford Leach in a guide to the contents of the British Museum.
Hawaiian honeycreepers were once placed in their own family, Drepanididae, but DNA analysis found them closely related to the Carpodacus rosefinches. They are now placed within the Carduelinae subfamily of the finches and are famous for a wide range of bill shapes produced by adaptive radiation.