TOUCANS are among the most characteristic birds of tropical America, and for well over a century they have probably been depicted, in drawings and words, more frequently than any other neotropical family except hummingbirds. Yet even today there is a dearth of information about their habits, especially their nesting. Beebe (Beebe et al., 1917) described the nests, eggs, or nestlings of several toucans of British Guiana. Van Tyne (1929) made a careful study of the breeding habits of the Keel-billed Toucan (Ramphastos suiphuratus) in Panama, but his observations were cut short by the destruction of the nestlings. Wagner (1944) published notes on the breeding of the Emerald Toucanet (Aulacorhynchus prasinus) in southern Mexico. Apparently the earliest account of all stages in the nesting of a toucan, from laying to the departure of the nestlings, was my life history of the Blue-throated Toucanet (A. caeruleogularis) (Skutch, 1944). Important details of the nesting of this small highland toucan were added in a later account (Skutch, 1967). Observations on the breeding and general behavior of two species of middle-sized ara~ari toucans were recorded in another paper (Skutch, 1958). The present contribution to the natural history of toucans is based largely upon studies made at Finca La Selva in 1967 and 1968. This property, largely covered by primeval rain forest but with extensive riverside plantations of cacao, lies along the left bank of the Rio Puerto Viejo just above its confluence with the Rio Sarapiqui, a tributary of the Rio San Juan in the Caribbean lowlands of northern Costa Rica. Slud (1960) has well described the lofty, epiphyte-burdened forest with an undergrowth consisting largely of small palms, and given an account of its avifauna remarkably rich in species. Including their enormous bills, adult Keel-billed Toucans (which in other writings I have called Rainbow-billed Toucans) range from about 17 to 22 inches in length. Even without the many-hued bill, this toucan with contrasting areas of white, yellow, red, and black would be a spectacular bird; attached to a boldly patterned body, the delicately tinted bill makes it one of the most colorful inhabitants of the Central American forests. In the southern race (R. s. brevicarinatus), the greater part of the swollen upper mandible is yellowish green; there is an elongated patch of bright orange along the basal half of its cutting edge; and the terminal fifth (approximately) is dull red. The lower mandible is green at the base, then light blue, then dull red on approximately the terminal eighth. Both man-