CAPRIMULGIDAE Nightjars and Nighthawks FAUNA PARAGUAY

CAPRIMULGIDAE - NIGHTJARS AND NIGHTHAWKS
Fifteen Paraguayan species in two subfamilies. Fossil Caprimulgids date back to the Upper Eocene. Nightjars are little-known and mysterious nightbirds, about which a great deal of negative legend has been created - not least the idea that they "suck goats", in fact the name Caprimulgid translates literally as goatsucker. Nightjars are mostly nocturnal and are most active at dawn, dusk and during full moon. They usually leave the roost after sunset and return prior to sunrise. They are vocal during the breeding season, but often quiet at other times of year. Some species are also capable of making mechanical sounds. Most species are solitary when not breeding, but some are more gregarious - especially amongst the nighthawks.
They are small to medium-sized birds with long wings, large heads and a small weak bill. Nightjars are renowned for their cryptic plumage which provides remarkable camouflage against the substrate. When approached, roosting nightjars close the eyes, shrink the neck and flatten the plumage to maximise camouflage and are ready to fly as soon as they deem necessary. The plumage is soft and easily displaced and many species are sexually dimorphic. White wing and tail markings often present in the male likely play a signalling role. The enormous gape is assisted by specialised jaw musculature which enables the bill to be opened both vertically and horizontally at the same time. Nightjars often roost in exposed positions and cope with heat stress by opening the bill, fluttering the throat and increasing blood flow to the gular area. Nostrils are raised and situated basally on the top or the upper mandible. Nightjars lack a crop, have a complex hypotarsus and small basypterygoid processes. Most species have long, slender wings, being more rounded in Nyctiphrynus and modified in Eleothreptus. Low wing-loading makes them agile in the air, the flexible tail being used as a form of rudder. There are 10 primaries, 11-14 secondaries and 10 retrices. Males of some species show elongated tail feathers, particularly exaggerated in Hydropsalis. The tarsi and are short and the feet small and weak. The tarsi are proportionately longer in terrestrial species such as Podager. Toes are partly webbed, there are four phalanges in the outer toe and two in the hallux. The claw of the middle toe is pectinate, likely with a grooming function. Nightjars are visual feeders and large lateral eyes give improved vision in low-light conditions. There are 14 cervical vertebrae and the metasternum has one notch on each side. Nightjars exhibit "eye-shine" when flashed with an artificial light source. This is a result of light reflecting from the tapetum which is located behind a layer of photoreceptors at the back of the eye. The tapetum acts to increase light entry into the eye for night vision.
Most nightjars are ground nesters with monogamous breeding systems. They are generally non-colonial breeders. Males establish and defend territories. The clutch is small, often two, smooth, elliptical eggs with pale colouration. The colouration likely assists with their location at night, but means that during the day incubating nightjars must sit tightly to avoid revealing the location of their nest to predators. Eggs hatch asynchronously, chicks having a downy covering on hatching but rapidly developing their first feathers. Moult is annual after breeding, some migratory species having a suspended moult that begins on the breeding grounds and reaches completion on the wintering grounds. Primary moult ascends, secondary moult descends and tail feathers are moulted from the central feathers outwards.

Subfamily Chordeilinae: "Nighthawks"
Includes the genera Lurocalis, Podager, Chordeiles and Nyctiprogne. Behaviour aerial, food being taken on the wing in a similar manner to swifts. They have a desmognathous palate and lack rictal bristles. Frequently active by day. Those that perch on branches tend to perch lengthways along the branch. Nighthawks appear to have originated and diversified in South America.
Lurocalis - Long-winged and short-tailed with bat-like silhouette. Short tarsi feathered on the front. Arboreal, nesting on bare tree branches. Lack white markings on wings.
Podager - Large with extensive white on plumage and sexual dimorphism. Gregarious, migratory and partly diurnal. Lays eggs directly onto the ground.
Chordeiles - Long-winged and slightly forked tails. Both species migratory. Sexual dimorphism indicated by extent of white markings on throat, tail and wings. Roost on perches or the ground, nest on the ground.
Nyctiprogne - Small with short bill and concealed nostrils. Gregarious. Lacks white wing markings. Lays eggs directly onto the ground.

Subfamily Caprimulginae: "Nightjars"
Includes the genera Caprimulgus, Nyctidromus, Nyctiphrynus, Hydropsalis and Eleothreptus. Nightjars are less aerial in behaviour and hunt by making short sallies from the ground or a perch. They have a schizongnathous palate and stiff rictal bristles around the gape attached to sensitive muscles in the skin. Mainly nocturnal. Those that perch on branches tend to perch perpendicular.
Caprimulgus - Long, pointed wings and feathered tarsi. Sexual dimorphism. Roost and breed on the ground, building no nest.
Nyctidromus - Long bare tarsi adaptation to terrestrial habits. Sexual dimorphism. Breeds and roosts on the ground.
Nyctiphrynus - Prominent tubular nostrils. Rictal bristles decurved. Dense crown feathers protrude forming a rim above the eyes. Unfeathered tarsi and rounded tail. Breed and roost on the ground, but perch freely in trees.
Hydropsalis - Elongated tail, especially in male. Strongly sexually dimorphic. Breed and roost on the ground.
Eleothreptus - Dumpy with large head and eye. Short, square tail and modified wing shape. Partially feathered tarsi. Broad bill and very long rictal bristles. Strong sexual dimorphism. Breeds and roosts on the ground. Males produce mechanical wing sounds during display.

REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Cleere N & Nurney D 1998 - Nightjars: A Guide to the Nightjars and Related Nightbirds - Pica Press.
Cleere N 1999 - Caprimulgidae Handbook of the Birds of the World Volume 5 - Lynx Ediciones.