A buzzing note of inflection from one direction, followed by a fainter one in the distance. Only a shimmer of a silent shadow is seen, but where it lands a large red eye reflects brightly. Tiptoeing carefully to get closer, a mottled brown feathered ball comes into view. Most of the time it’s practically impossible to approach closely, but the damp grass allowed me to crouch right next to the bird and get a rare glimpse at its chocolate brown iris. Called the common paraque (Nyctidromus albicollis), this crepuscular bird belongs to a group (Strisores) that includes the extremely cryptic potoos and oilbird of the New World as well as the frogmouths and owlet-nightjars of the Old World. Potoos and frogmouths perch high in the trees, resting upright by day with the eyes closed to resemble a broken branch or trunk, whereas the oilbird (Steatornis caripensis) primarily hides itself along ledges within caves. Paraques, on the other hand, are generally terrestrial, only taking to the air when on the hunt. Even their nests are made on bare ground, with one or two pinkish eggs laid in a slight depression which prevents them from rolling away. Both the male and female incubate the eggs and take turns throughout the day and night.
Paraques have enormous eyes for their body size. Coupled with long thick rods in the retina and a tapetum lucidum, they have excellent vision under low light conditions. After the sun sets, they will sit out in the open, hopping around and snatching up flying insects that they detect against the backdrop of the night sky. Increasing light levels do improve their foraging success, and paraques extend the duration of their hunts on full moon nights. Artificial lights are also thought to influence their foraging patterns. In the U.S., I frequently observe nighthawks (Chordeiles minor), another caprimulgid, convene to forage around tall stadium lights. At rest, a paraque’s eyes are the most prominent facial feature, but perhaps even larger is what lies concealed — an enormous mouth — a characteristic shared with the potoos, frogmouths, and owlet-nightjars. Having a large gape increases the size of potential insect prey, and specialized rictal bristles (actually modified feathers) droop over the beak to protect the eyes from a flailing insect’s appendages in lieu of eyelashes. Among nocturnal Strisores, oilbirds are an outlier in being exclusively frugivorous, and even more unique in that they are the only species of fruit-eating nocturnal bird. Capable of flying around in caves under complete darkness, they remarkably use echolocation to navigate by emitting clicks like a bat, though much lower in frequency. Hopefully next time I explore caves in South America, I’ll be lucky to find one!
Paraques & potoo photographed in situ 
A common potoo (Nyctibius griseus) sits atop a tall broken tree in the rain, relaxing from a typical vertical posture to conserve body heat. Potoos are not only experts in camouflage, but are well attuned to detect movement from all angles. The eyes sit on opposite sides of the head, giving them a wide field of view, and they protrude outward to prevent obstruction from the surrounding feathers. Astonishingly, potoos also have two notches on the upper eyelids that enable vision even when the eyes are completely closed. Along with dilation of the pupils, this grants them very high sensitivity to light within those two very small apertures. Given potoos’ great reliance on remaining undetected to avoid predation, it’s uncertain what the benefits of the eyelid notches are, and this is further complicated by reports of them opening their eyes in response to a disturbance… revealing conspicuous yellow irises. Potoos remain enigmatic creatures due to their sedentary lifestyle and reluctance to perform behaviors while being observed; only their nesting ecology and vocal repertoire have thus far been described. It would be really interesting to discover variation among the seven Nyctibius species and how they compete with owls and nightjars for acoustic space and prey.