Aerodramus francicus commonly known as the Mascarene swiftlet belongs to the Apodidae family, which superficially is similar to swallows, but are not closely related to any of the passerine species. Mascarene swiftlets measure 10.5 centimeters. They have a forked tail; dark brown upperparts with a whitish rump, and pale brown underparts. This species is native to Mauritius and Reunion and breeds in colonies in caves and lava tunnels.
The Mascarene swiftlet can be found over a wide range of habitats. It feeds on winged insects in flocks at approximately 20 meters above ground. It can be seen flying low over lakes and during cloudy weather. Breeding and nest building occurs year-round. The nests are bracket shaped and made using lichen filaments held together with saliva on cave roofs. The clutch is usually sized for 2 eggs and the incubation period varies between 21 to 23 days, while the fledgling period lasts between 45 to 55 days.
Its moderately small population and small range have warranted the species to be listed as ‘Near Threatened’ in the IUCN Red List. Although the population in Réunion has increased substantially, the population in Mauritius has declined, rendering the establishment of accurate population trends challenging.
In the 1970s, the species was much less common in Réunion than Mauritius, however the population numbers have declined noticeably in Mauritius in the last century, continuing through the last 20 years. Surveys in the 1990s revealed colonies in 34 caves, but with the complete removal of birds from a further 19 caves, the population is estimated at 2,244 to 2,610 birds.
The major threats to swiftlets are the vandalism of caves, solid waste disposal in caves and collection of birds’ nests for soup. These threats are exacerbated by a shortage of suitable nest-sites. No specific conservation actions are under way; continued surveys to monitor population trends have been recommended.
Non-breeding Mascarene swiftlets join nesting colonies and collaborate in building nests, although not using the nests themselves.