See text Aerodramus is a genus of small, dark, cave-nesting birds in the Collocaliini tribe of the swift family.

Echolocation, DNA sequencing and parasitic lice have all been used to establish relationships, but some problems, such as the placement of the Papuan swiftlet are not fully resolved.

[3] Several of the species are restricted to small islands, and their limited range can make them vulnerable, like the Seychelles, Whitehead's and Guam swiftlets.

[3] Clutch size depends on the location and the food source, but generally Aerodramus swiftlets lay one or two eggs.

[10][11] The Aerodramus swiftlets' echolocating double clicks are within the normal human hearing range and up to 3 milliseconds apart, with the interval becoming shorter in darker locations.

[12] The use of echolocation was once used to separate Aerodramus from the other non-echolocating cave swiftlet genera Collocalia and Hydrochous (virtually nothing is known about Schoutedenapus).

However, recently, the pygmy swiftlet, Collocalia troglodytes, was discovered making similar clicking noises both inside and outside its roosting cave.

[13] It has recently been determined that the echolocation vocalizations do not agree with evolutionary relationship between swiftlet species as suggested by DNA sequence comparison.

[14] This suggests that as in bats, echolocation sounds, once present, adapt rapidly and independently to the particular species' acoustic environment.

Instead of incorporating twigs, feathers and straw like others in the genus, these two swiftlets make their nest only from strands of their gummy saliva, which harden when exposed to air.

Over the past twenty years, the high demand for the nests of these Aerodramus species has had an adverse effect on their populations.

[3] Early authors had doubts about the material used to make the nest, with whale and fish sperm and sea foam being proposed as the basis for construction.

Even in the 1830s, when the use of saliva had been fairly well established, it was believed that it was only a cement to bind a sea plant which provided the bulk of the gelatinous material of the nest.

[20] The survival of lice in most of these transfers was significantly reduced in proportion to the mean difference in feather barb size between the donor and recipient species of hosts.