Aerial insectivores feed on flying insects whilst on the wing. These birds are presented in two sub-groups; Diurnal feeders and Nocturnal feeders. They account for 313 of the worlds species.
Diurnal feeders.
Swifts (100 species) are probably the best known example of birds which feed almost exclusively on flying insects in an aerial habitat. They use their own saliva to make nests on vertical surfaces and even on the roofs of caves. In fact the place they choose to nest is one of the factors which enable one to differentiate one species from another. Swifts are found everywhere except the two Polar Regions and deserts, where few insects are available.
Swifts cling to surfaces rather than perch on them and they tend to do it in very inaccessible places, like behind water falls. Tom G kindly provided me with access to his birding photographs from a trip to Argentina in October 2011. The Great Dusky Swift (right) was photographed by Tom G at the Iguazu falls.
Treeswifts (4 species) are found only in the Indo-Malaysian region where they can be seen perched in tall trees waiting to catch insects which pass by.
Swallows and Martins (86 species) look quite like Swifts and nest in a similar manner but use mud instead of saliva. Africa and Central / Southern America each have many endemic species and a few are found worldwide. Their habitats tend to be over waterways and marshy land where insects are plentiful. They take insects at a lower height than the Swifts. Species have established niches which relate to the height at which they feed.
Wood Swallows (11 species) are endemic to Australia and New Guinea where they tend to favour eucalyptus forest and woodland. Although they are mainly insectivores they will eat some plant materials and perhaps nectar.
Nocturnal feeders.
Pratincoles (8 species) are Old World birds found mainly in Africa, Australia and Europe where they favour wetland and inland water areas. They are ground nesters and tend to feed at dawn and dusk.
Nightjars, Nighthawks, Potoos, Owlet-Nightjars (104 species) are all nocturnal birds found in most parts of the world, particularly in tropical regions which have abundant insect life. Habitats range from sandy scrubland, through fields with rocky outcrops, to woodlands, brush and forest edges.
They are ground and tree nesters which rely on camouflage as they sleep during the day. They are very agile and feed on flying insects at dawn and dusk.
All these birds blend in very well with their background when they are at rest as these two images of a Lesser Nighthawk (left) taken at Mc. Allen in Texas and the Common Potoo (right) taken in Tobago, illustrate.
Fossil evidence suggests that Swifts, Nightjars and Potoos probably evolved about 60mya with the Swallows evolving a different lineage much more recently.