Exercise 1 solution

(a) 1901 - 1889 = 12 years between Bailey's Birds through an Opera Glass and Selous's Bird Watching.
(b) 1934 - 1901 = 33 years between Selous's book and Peterson's guide.
(c) 1934 - 1889 = 45 years between the first US field guide named in the chapter and Peterson's guide (12 + 33 = 45).

Meaning: the guide, the name and the boom came in that order. A field guide existed before the hobby had its familiar name, and the largest North American growth came decades later.