Part (a) is a photo of rufous hummingbird in flight. It has long, straight and very narrow beak, a white breast, reddish-brown face, upper parts, flanks and tail. Part (b) is a plot of oxygen consumption over the course of a day, from pre-dawn to post-dusk. Dawn, noon and dusk are marked on the horizontal axis and grey shading marks the two periods of darkness. The oxygen consumption scale along the vertical axis is non-linear and is marked from one to 50, in units of nanolitres of oxygen per gram per hour. In the hours before dawn, oxygen consumption is at a constant low level of one nl per gram per hour; it then rises rapidly, reaching 20 nl a couple of hours into the day. By noon it reaches 30 nl, and peaks at around 40 nl in the late afternoon. Then, just before dusk, consumption falls very rapidly and is back to the baseline level of around one unit as soon as darkness descends.