From the introduction:
"The studies included in this book have diverse histories. Some, such that of the Ringed Kingfisher, were made long ago and withheld from publication in the hope of adding to them – a hope that was never fulfilled. Others, including those of the Pauraque and the Tawny-bellied Euphonia, have grown slowly over the years. Still others, among which are those of the White-fronted Nunbird, the Black-faced Grosbeak, and the Bronzy Hermit, were made rather recently. [...] About half of these studies were made in the Valley of EI General, at the head of the Río Térraba drainage on the Pacific side of southern Costa Rica, and especially on our farm, "Los Cusingos," situated at about 2 400 feet above sea level beside the Río Peña Blanca, an affluent of the Río Térraba."