Justification of Red List Category
This species is confined to three small islands where, despite its adaptation to artificial habitats, its population is suspected to be under threat as a result of successive droughts and an increasing human population. Its future on one island, in particular, is precarious, and the overall population trend is uncertain. The discovery of a relatively large population on Fogo, where it occurs commonly in plantations and crops, suggests that it may be less threatened than previously feared, and a re-assessment of its extent of occurrence using a minimum convex polygon means that the species now warrants listing as Vulnerable.
The population was estimated at c.500 pairs in the early 1990s, and was thought to number 1,000-1,500 birds based on its known range in 2007 (C. J. Hazevoet in litt. 2007). However, conservative estimates of 500 pairs on Fogo mean that the total population is likely to be higher, likely numbering 1,500-2,000 mature individuals, roughly equivalent to 2,200-3,000 individuals in total. Full censuses were never carried on Fogo or Santiago. The numbers on Santiago could be higher than previously thought because the bird is now known to occur in all vegetated areas of the island, whereas in the 1990s it was thought to be absent from the north of the island (H. Batalha in litt. 2016). On Fogo, a volcanic eruption in 2014 does not seem to have affected the extent of area occupied by the bird, but the bird is absent from areas where it had been previously found on the forest of Monte Velha following the forest fire of 2015. However, the size of the birds’ territories is unknown, and could be larger than in closely related species; this means that the numbers estimated based on replies to playbacks may or may not correspond to the actual numbers (in recent surveys, the same colour-ringed bird replied to playback lures from locations that could have considered two adjacent territories [H. Batalha in litt. 2016]). Surveys on S. Nicolau in three occasions in 2014 and 2016 found 12 – 13 territories each time, and the real number is not likely to be much higher. There are probably a minimum of 20 birds and a maximum of 50 on that island.
Despite the discovery of a large population on Fogo in 2004 and a report from Tarrafal on Santiago, the overall population was suspected to be declining owing to habitat loss, although substantive evidence of this is lacking (C.J. Hazevoet in litt. 2007). The Fogo population favours coffee plantations and introduced crops and the population may yet prove to be stable.
While the population on S. Nicolau seems to have decreased between the time of its discovery, in the 1860s, and the 1920s, the numbers seem to have stabilised, with approximately the same numbers of birds found in 1998, 2004, 2014 and 2016 (H. Batalha in litt. 2016). On Santiago, the bird was considered to be absent from the northern part of the island in the 1980s and 1990s, but currently it can be found in all latitudes (Batalha et al. 2016); it is not clear whether the birds was really absent on the northern part of the island in the 1980s/1990s or were simply undetected, so current population trends are difficult to infer (H. Batalha in litt. 2016), and it is possible that the species may have as much as doubled in population size (C. Hazevoet in litt. 2012).
Acrocephalus brevipennis was once believed to be confined to Santiago, Cape Verde Islands, where it was though to be locally distributed. It has most likely died out on Brava (no records since 1969 and formerly scarce) and was believed to have died out on São Nicolau (where it was formerly numerous). However, a previously unreported specimen collected on São Nicolau in October 1970 was discovered in the collection of the Centro de Zoologia, Lisbon, providing the impetus for a thorough search of the island (Hazevoet 1999a) and, in 1998, surveys located eight territories confined to the north-west of the island (though its long-term prospects for survival here are poor) (Hazevoet et al. 1999). In October 2004 a population was discovered on Fogo, and it has since been found to be widespread across the northern half of the island between 200-975 m, with the total population on the island conservatively estimated at 500 pairs (Hering and Hering 2005, Hering and Fuchs 2009). In addition, the species may have formerly occurred on Santo Antão (Hazevoet 1995). On Santiago, the species was recently reported from Tarrafal, far to the north of the species's known range (C.J. Hazevoet in litt. 2007). The total population was estimated at c.500 pairs in the early 1990s (Hazevoet 1995), and thought to number 1,000-1,500 birds based on its known range in 2007 (C.J. Hazevoet in litt. 2007). However the discovery of relatively large numbers on Fogo means that the total is probably considerably higher.
Surveys to detect this species were carried out in 2013, 2014 and 2016 in a joint project between the University of East Anglia, UK, and Cape Verde Natural Parks of Fogo (Fogo), Serra Malagueta (Santiago) and Monte Gordo (S. Nicolau). Currently, the bird is known to be absent from Brava and Santo Antão (Batalha et al. 2016); anectodal reports could not be verified despite extensive searches and could have consisted of vagrant birds (H. Batalha in litt. 2016). On Fogo, it can be found in densely vegetated areas between 299 and 1384m, including coffee plantations, inaccessible ravines covered in invasive Lantana camara and Furcrarea spp., and the forest of Monte Velha (Batalha et al. unpublished data). On Santiago, it can be found in densely vegetated areas across the island, between 6 and 1,039 m, and in various habitats, from lowland plantations (e.g., Praia, Cidade Velha, Chão Bom, Achada Tenda, Pedra Babejo) to mountain forests (Serra Malagueta and Monte Tchota), and sugar cane plantations in Praia to Prosopis spp. shrub thickets in Tarrafal (Batalha et al. unpublished data). On S. Nicolau, however, territories seem to be confined to a central humid area comprising part of the Natural Park of Monte Gordo and the valleys of Queimadas, Fragata and Covoada, between 162 and 733m (Batalha et al. unpublished data). Extensive, thorough surveys located only 12-13 confirmed territories, either in reed patches or mango trees, so the actual number is not likely to be higher than 20-30 in the entire island of S. Nicolau (Batalha et al. unpublished data). The bird is not present either in the forest of Monte Gordo, on the plantations of Fajã or in the far-east Prosopis spp. thicket of Carriçal (Batalha et al. unpublished data). Genetic data confirm that there have been no recent colonisations or re-colonisations of either of the islands (Batalha et al. 2016).
Its original habitat was probably scrub on mountain slopes and reedbeds in valleys (Hazevoet 1993). It is now found in a broad range of habitats up to 1384 m (H. Batalha in litt. 2016). The habitats occupied at lower elevations include well-vegetated valleys (especially with patches of reeds), reedbeds, woodland, agricultural areas, and gardens in villages and small towns, notably near running water (Hazevoet 1995). In 2004, a population in the interior of Santiago was noted inhabiting Eucalyptus forest with dense, bushy undergrowth at 800-1000 m (J. Hering and H. Hering in litt. 2004). On São Nicolau, it inhabits small, dense stands of cane Arundo donax along dry riverbeds, often with shrubs and fruit trees (Hazevoet et al. 1999). On Fogo, it inhabits coffee plantations with scattered fruit trees and maize fields with coffee bushes in areas characterised by narrow, shrub-filled ravines at 490-950 m, and the forest of Mount Velha (Hering and Hering 2005, Hering and Fuchs 2009, H. Batalha in litt. 2016). It may also in habit cultivated areas around dams (H. Batalha in litt. 2016). It breeds mainly in August-November, but the breeding season may be extended in response to local rainfall (Hazevoet 1995).
Habitat loss due to the combined effects of successive droughts and an increasing human population may be responsible for the population decline and restriction of its distribution on Santiago (C.J. Hazevoet in litt. 2000). This is almost certainly the cause of its decline on São Nicolau and extinction from Brava, where continuing desiccation has restricted agricultural productivity (Hazevoet 1993). In addition, disease and enviromental catastrophies are potential threats to these island populations (Hazevoet et al. 1999). A recent forest fire on Fogo destroyed a large part of inaccessible forest where the species possibly existed (H. Batalha in litt. 2016), and so forest fires, and any future increase in fire frequency could be very harmful to this species. The removal of invasive plant species, such as reed removal by farmers on S. Nicolau, could possibly reduce the available habitat for this species in areas where there is no natural habitat (H. Batalha in litt. 2016). There is suspicion that it may be predated by birds (e.g. kestrel, crows), possibly rats and even humans (H. Batalha in litt. 2016).
Conservation Actions Underway
Wildlife Protection Laws, proposed in the late 1980s, have still not materialised and, as of 2007, the species still has no legal protection (C.J. Hazevoet in litt. 2007). It is found in three protected areas: Parque Natural do Fogo, Parque Natural da Serra Malagueta and Parque Natural de Monte Gordo. It is considered a CITES species by national authorities, and any work conducted in the natural parks is subjected to permission by the local authorities. There is regular monitoring on Natural Parks of Fogo and Serra Malagueta, and on S. Jorge dos Órgãos. There is also a monitoring scheme in place at Natural Park of Monte Gordo, but it has been irregular over the last few years due to the lack of specialised staff (H. Batalha in litt. 2016).
14-16 cm. Medium-sized warbler. Dun-brown above with warm buff belly and flanks and creamy throat and breast. Long, pointed bill, black legs and toes. Sexes similar. Voice Loud, explosive song with clear whistles and blurred churring heard throughout the year, but most intense between August and November. Hints Small parties sometimes feed communally in fruiting fig trees Ficus spp., together with Blackcap Sylvia atricapilla (Hazevoet 1995).
Text account compilers
Ekstrom, J., Symes, A., Taylor, J., Shutes, S., Martin, R, Westrip, J.
Batalha, H., Hering, H., Hazevoet, C., Donald, P., Hering, J.
BirdLife International (2019) Species factsheet: Acrocephalus brevipennis. Downloaded from http://www.birdlife.org on 25/06/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/06/2019.