From 1936 to 1998 I kept notes on the Riverside Wren (Thryothorus semibadius) in southern Pacific Costa Rica. Early in this interval, the wrens lived chiefly along the shores of wider streams flowing through the forests and around marshy openings in the lowlands. With widespread deforestation, they tended to forage and nest farther from the watercourses. Their short, ringing songs sound above the clamor of mountain torrents. They eat small invertebrates. At all seasons they sleep alone or two or three together, in well-enclosed nests such as they occupy for breeding. Only the female incubates the two eggs, taking long sessions and long recesses. The incubation period is 18 or 19 d. Both parents attend the young. The nestling period is 16 d. The parents lead newly emerged fledglings to sleep in a nest with their mother. For a year and a half, I followed the activities of a family of four that lived in our garden.