Justification of Red List Category
This species is listed as Near Threatened because it is thought to have a moderately small population within a small range. The population on Réunion has increased substantially but that on Mauritius has declined, so the overall population trend is difficult to judge. Any evidence that the population is smaller than this or is declining overall may qualify the species for uplisting to a higher threat category.
The population on Mauritius was estimated at 2,244-2,610 individuals (G. Middlteon per C. Jones in litt. 2000), and the population on Réunion is likely to be far larger, with some of the largest colonies thought to contain 5,000 pairs (St Denis à La Possession) and 1,000 pairs (Bras de la Plaine) (V. Tatayah, N. Laurent and F.-X. Couzi in litt. 2018). The overall population size has not been estimated, but based on these figures, it may be precautionarily placed in the range 10,000-19,999 mature individuals.
Over recent years, the population on Réunion has increased substantially (A. Cheke pers. comm. 2000), whilst that on Mauritius has declined, making it difficult to judge the overall population trend. While it may be possible to infer that the species is in decline as a result of the ongoing threats within its range, it is currently not possible to clearly quantify the rate of decline.
This species is endemic to Réunion and Mauritius, where it breeds colonially in caves and lava tunnels (Cheke 1987). In the 1970s, the species was much less common on Réunion than Mauritius (Cheke 1987). More recently, discoveries on Réunion of several large colonies indicate that the population has since increased substantially to over 10,000 mature individuals (V. Bretagnolle in litt. 1999, M. Le Corre in litt. 1999, A. Cheke pers. comm. 2000), including a small number of sites with more than 1,500 birds (Barré et al. 1996, A. Cheke pers. comm. 2000, Le Corre and Safford 2001). On Mauritius, numbers have declined markedly in the last century, continuing through the last 20 years, with surveys in the 1990s indicating habitation of 34 caves, but complete removal of birds from a further 19. The population was estimated to be a minimum of 2,244-2,610 individuals (G. Middleton per C. Jones in litt. 2000).
The species occurs over a wide range of habitats (del Hoyo et al. 1999). It feeds on winged insects (e.g. Diptera, flying ants and anthomyid flies) in flocks, usually 20 m above the ground, but lower over lakes and during cloudy weather. Nest building and breeding may take place virtually all-year-round. Nests are bracket-shaped and constructed using lichen filaments, held together with saliva on cave roofs, and even non-breeding individuals may join nesting colonies and build, but not use nests (Safford 2013). Two eggs are typically laid, rarely one, and the incubation period is probably 21-23 days, followed by a probable fledging period of 45-55 days (del Hoyo et al. 1999).
Human consumption and other activities at colonies are the principle threats on Mauritius (Cheke and Hume 2008). In extreme cases, caves are completely closed-off (C. Jones in litt. 2000, V. Tatayah in litt. 2019). Development and disturbance of caves for tourism may threaten colonies on both Mauritius and Réunion (V. Tatayah in litt. 2019). The largest known colony, occupying a railway tunnel in Réunion, has been under pressure from infrastructural work and may be vulnerable to the recommencement of train usage (V. Tatayah in litt. 2019). Use of insecticides, especially in Mauritius, may have an impact on food resources (V. Tatayah in litt. 2019).
Conservation Actions Underway
No targeted conservation action is known for this species.
Text account compilers
Symes, A., Taylor, J., Warren, B., Westrip, J., Pilgrim, J., Robertson, P., McClellan, R., O'Brien, A., Smith, D.
Bretagnolle, V., Cheke, R.A., Couzi, F.X., Jones, C., Laurent, N., Le Corre, M. & Tatayah, V.
BirdLife International (2021) Species factsheet: Aerodramus francicus. Downloaded from http://www.birdlife.org on 20/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 20/10/2021.