Data Zone
Justification of Red List category
This species is known only from a few specimen and sight records, but there is no clarity on the true extent of its distribution and hence on the population size or trends. Until the taxon is clearly delimited and it is possible to reduce the uncertainty over the range and consequently the plausible range of population size and impact of potential threats, it is classified as Data Deficient.
Population justification
The population size of this species cannot currently be quantified due to the uncertainty over the delimitation of the species' range. If it is restricted to the island of Bioko there are records possibly relating to this species from several high altitude sites, with maximum flock sizes of fewer than 50 individuals. Therefore there is the possibility that the population is small or very small. Equally, if individuals reported in Cameroon, mainland Equatorial Guinea and Angola (Dowsett-Lemaire and Dowsett 1999, Bowden 2001, Mills and Dean 2007, Cooper et al. 2016), currently treated as unidentified (Cooper et al. 2017), are this species, then the population is plausibly large and secure. There is no information on trends from any part of the potential range.
Trend justification
The population trend is unknown: there is no information even from restricted areas of the plausible range such as Bioko.
The occurrence of Apus sladeniae is clouded by the difficulty of identification and disagreement over its taxonomic status as a species. Specimen records come only from the island of Bioko, Equatorial Guinea (six collected in December 1903/January 1904 [Ogilvie-Grant 1904]), west Cameroon (one from Mount Kupe in the Bakossi Mountains [as 'Apus melanonotus' von Reichenow 1907]) (Brooke 1970), Angola (two from Mount Moco originally assigned to A. barbatus roehli) (Traylor 1960, Brooke 1970, da Rosa Pinto 1983) and south-east Nigeria (one collected in 1961 on the Obudu plateau and originally identified as A. apus) (Parker 1971, 1972, Elgood 1981, P. Hall in litt. 2016).
A population of swifts in northern Liberia considered to be A. barbatus may be of this form (del Hoyo et al. 2015, 2020).
Reported possible sightings have also come from mainland Equatorial Guinea, with c.10 birds at Moca in Monte Alen National Park in January 1998 (Dowsett-Lemaire and Dowsett 1999) followed by numerous sightings of all-dark Apus species thought most likely to be this species during ornithological surveys in 2013 and 2014 (Cooper et al. 2016, eBird 2022).
On the island of Bioko ornithological work in 2016 similarly resulted in numerous sight records of a dark Apus species around Moka in the south as well as at Caldera de Luba at c. 1000 m and near the summit of Pico Biao (c. 2000 m) (Cooper et al. 2017, eBird 2022), despite no records from the island since the specimens collected in 1903/4 (Pérez del Val 1996). These swifts are described as being vocally similar to African Black Swift A. barbatus and to match the phenotype of the specimens from which A. sladeniae was described (Cooper et al. 2017). It is assumed that these individuals represent the same form as the specimens from which this species was described, hence these areas are here considered the minimum current occupied range.
There were reports of A. barbatus from Mount Kupe in Cameroon in June 1990 and March 1998 ascribed to A. (b.) sladeniae by geography and their dark throats (Bowden 2001): there has been the suggestion that A. sladeniae may vacate Bioko during the non-breeding season and move to highland areas of adjacent mainland Africa. An observation of two individuals that may have been this species from Príncipe in August 1997 would surely have been migrants, but may not have been this species and remain unconfirmed (de Lima and Melo 2022). There is no further evidence for movements in the species. More recent reports from Cameroon have not attempted to assign individuals of this phenotype to a species, due to uncertainty in identification. This may also be the cause of the lack of any further reports from Nigeria, although this can also be interpreted as evidence that the 1961 record was actually a vagrant individual and it is not a regular part of Nigeria's avifauna (P. Hall in litt. 2016).
Investigations in Angola located a breeding Apus species ascribed to this species at Njelo Mountain above Kumbira forest along the escarpment, with the same form also present at Mount Soque (Mills and Dean 2007) close to the site of the previous records assigned to A. sladeniae at Mount Moco (Brooke 1970, Dean 2000, Mills and Dean 2007). The calls heard from a breeding adult here were however described as heard to call 'unlike those of the African Black Swift, and with some similarity to the Little Swift Apus affinis' (Mills and Dean 2007).
Further work is required to clarify the occurrence of this form and the relationships between the dark Apus species that occur in west Africa: the evidence presented here indicates the uncertainty over both extent of occurrence and the occupancy of this species as noted by Cooper et al. (2017). It may be a taxon restricted to the highest parts of the island of Bioko, where it may be resident or may migrate to the mainland in the non-breeding season, or it may be patchily distributed across highland areas south as far as Angola. Occupancy could be as little as a handful of suitable high elevation areas on Bioko, or extend to numerous montane areas over a large part of central western Africa.
It is probably primarily a mountain species: all records are from above 1,000 m although the specimen records from Bioko do not possess elevation data. Recent observations of Apus species assumed to be this species on the island have also been from above 1,000 m. The male specimens from Bioko had enlarged testes when collected at the end of December/early January, hence this is assumed to be the breeding season there. In Angola, individuals assigned to this species were found breeding in rocky crevasses above forest in August and October (Mills and Dean 2007).
Threats to the species are unknown.
Conservation Actions Underway
None is known.
Text account compilers
Martin, R.
Contributors
Mills, M., Hall, P., Symes, A. & Westrip, J.R.S.
Recommended citation
BirdLife International (2024) Species factsheet: Fernando Po Swift Apus sladeniae. Downloaded from
https://datazone.birdlife.org/species/factsheet/fernando-po-swift-apus-sladeniae on 23/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 23/12/2024.