The Cape Verde Warbler: distribution, density, habitat and breeding biology on the island of Fogo Jens Hering and Elmar Fuchs ABSTRACT An expedition to the newly discovered breeding grounds of the Cape Verde Warbler Acrocephalus brevipennis, on the island of Fogo, Cape Verde, in October 2006, established that the species is widespread in the northern part of the island. Some 129 territories were mapped and the mean regional population density was 6.5 territories per 100 ha. A total island population of at least 500 breeding pairs is estimated. An analysis of the species’ habitat preferences showed that it occurs predominantly in coffee plantations, especially those intermixed with large fruit trees and bushes, and other introduced crops, especially maize. Spanish Flag Lantana camara is also an important habitat element, especially at higher levels and in inaccessible gorges. Cape Verde Warbler was not found in areas of introduced trees above the cultivation zone, although it breeds in similar habitat on Santiago island. Nine nests were found and described, and breeding behaviour at the nest studied.The species probably bred on Fogo prior to human settlement and has subsequently adapted to coffee plantations. If coffee crop management remains unchanged, the long-term survival of the Cape Verde Warbler on Fogo appears not to be under threat. rior to 2006, the breeding population Warbler was known from, it was last sighted in of Cape Verde Warbler Acrocephalus 1969 (Frade 1976; Hazevoet 1993, 1995), a Pbrevipennis, which is endemic to the Cape victim of desertification, habitat destruction Verde archipelago, was estimated at a maximum and increased predator pressure (from rats – of 500 pairs, and thought to be restricted largely both Black Rattus rattus and Brown Rats to the island of Santiago, where it is declining R. norvegicus occur on the island – and owing to habitat loss (BirdLife International domestic cats Felis catus). 2004; Clarke 2006). In 1998, the species was With this as a background, the discovery of rediscovered on the island of São Nicolau, Cape Verde Warbler on the island of Fogo in where it had last been recorded in 1924 October 2004 was all the more surprising. (Hazevoet et al. 1999). The eight pairs found During a three-day visit, 32 breeding territories there led to hopes that a healthier population were found in the northeast of the island, with may exist, but further studies in 2001 and 2003 males responding well to playback of song. One showed that the species probably occurs at only concentration was located in the coffee planta- three sites on the island, with a maximum of tions around the town of Pai António, at ten pairs (Hazevoet 2003; Donald et al. 2004). heights ranging from 490 m to 950 m asl, but a On Brava, the only other island that Cape Verde search in the northwest of the island failed to © British Birds 102 • January 2009 • 17–24 17 Cape Verde Warbler locate any birds. As only random searches were well as threats and possible conservation meas- possible in the short time available, it was ures, were key elements of the project, and most thought that more birds could be present in the effort was focused on territory mapping and fertile northern parts of Fogo, which is other- recording vegetation and habitat characteristics wise characterised by extremely dry conditions in breeding areas. (it is the hottest of the Cape Verde islands). Based on this initial survey, a total population Study area and methods for the whole island of more than 50 breeding The study area of some 2,000 ha lies in the pairs was estimated (Hering & Hering 2005, northern part of Fogo. Cultivated land, with 2006). During a short visit to the island in scattered village settlements and isolated habita- January 2006, the presence of the species was tions, dominates the landscape. The northeast again confirmed near Pai António (Hering trade winds ensure that this part of the island unpubl.). has a relatively moist climate (annual rainfall at The discovery of Cape Verde Warbler on 700 m asl is 1,100–1,200 mm), which creates Fogo prompted a more comprehensive survey ideal conditions for coffee cultivation. Coffee in October 2006, and that work forms the basis plantations, interspersed with fruit trees and of this paper. Current distribution, population bushes, extend from 300 to 1,000 m asl. The size and density, and habitat requirements, as area is extremely rugged and a number of steep gorges – the Ribeiras – make it difficult to negotiate. Line transects through representative sections of potentially suitable habitat were sur- veyed along passable tracks and existing trails between 19th and 31st October 2006. Singing males or pairs reacting to tape lures were mapped using a hand-held GPS unit, while nests and data on breeding biology were recorded where possible. The distribution of vegetation within each territory was recorded Territories and the degree of coverage for all plant species Fig. 1. Location of breeding territories, singing males or paired Cape Verde Warblers Acrocephalus brevipennis in the north of Fogo, Cape Verde, October 2006. 18 British Birds 102 • January 2009 • 17–24 Cape Verde Warbler was estimated following Braun-Blanquet (1964). 901–1000 Population 801–900 Population distribution 701–800 The October 2006 survey 601–700 established a core area of distribution in the region 501–600 surrounding Pai António height m asl 401–500 (fig. 1). Particular concen- trations were recorded on 301–400 the Monte Grande, in the 201–300 environs of Ribeira da Fajãzinha, and around 0 5 10 15 20 25 30 35 frequency of occurrence Ribeira Ilhéu. To the south- west of Pai António, birds Fig. 2. Vertical distribution of 129 records of Cape Verde Warbler Acrocephalus were recorded as far as brevipennis on the island of Fogo, Cape Verde Islands, in October 2006. Cutelo Alto, and west to Espia de Baixo and the spread, with the lowest territory at 222 m asl periphery of Ribeira Fonte Gatinha, with a rela- northwest of Feijoal, and the highest in Ribeira tively discrete area of distribution some 5 km Coxo, below Monte Velha, at 973 m asl. farther west, above Ribeira Ilhéu. The eastern Nonetheless, the main concentration of birds boundary lies close to Touril and Cova Lima, occurs between 300 m and 700 m asl. where a broad, bare tongue of lava stretches from Caldeira to the coast. An intensive search on the far side of the lava flow in the cultivated land around Corvo was unsuccessful. Three further territories, situ- ated between Monte Vaca and Ilhéu das Contendas in the northwest of Fogo, were unexpected and appear to be restricted to an isolated coffee plantation. Otherwise, all searches in the northwest of the island failed to locate any birds (Hering & Hering 2005), although further iso- lated occurrences in suitable Jens Hering areas cannot be ruled out. 11. Singing male Cape Verde Warbler Acrocephalus brevipennis in a coffee This possibility is supported bush near the nest, Pai António, Fogo, October 2006. Cape Verde Warbler by sightings near Atalaia and superficially resembles Reed Warbler A. scirpaceus but shows distinctly different proportions: a longer tail and bill, rather longer legs and larger feet, close to Ribeira Boga. and a short rounded wing with a fairly long first primary. Studies by Leisler However, no Cape Verde War- et al. (1997) established that it belongs with a subgroup of closely related blers were found in appar- Afrotropical Acrocephalus which includes the widespread Lesser Swamp ently suitable habitat in a A. gracilirostris and Greater Swamp Warblers A. rufescens. Compared with 200-ha afforestation project those of Reed Warbler the upperparts are drab olive-brown with a greyish cast to the crown and neck and a warm tinge to the rump and uppertail- on Monte Velha, which lies coverts.There is a narrow greyish-white supercilium, which is fairly distinct above the zone of cultivated above the lores and connects with a narrow whitish eye-ring.The chin and land. throat are creamy-white, contrasting with the olive-brown sides to the head The altitude of territories and the light grey-brown wash to the breast and flanks.The species’ movements through the trees and bushes recall those of a Hippolais found is shown in fig. 2. This warbler rather than an Acrocephalus.The sexes are similar in appearance reveals a wide altitudinal (birds were sexed in our study on the basis of song deliverance). British Birds 102 • January 2009 • 17–24 19 Cape Verde Warbler Population density Breeding habitat A total of 129 territories was located. Between Bannerman & Bannerman (1968) and Snow & Pai António and Ribeira Ilhéu, Cape Verde War- Perrins (1998) described the breeding habitat of blers occurred at an average density of 2.5 terri- Cape Verde Warblers on Santiago and São tories/100 ha (39 territories in 1,584 ha). In the Nicolau, as well as on the formerly inhabited core area, in coffee plantations near Pai António island of Brava. On Santiago, the species shows and farther east, the average density was 19 a preference for densely overgrown valleys and territories/100 ha (90 territories on 468 ha). watered plantations as well as small human set- This gave an average density for the whole study tlements with sufficient vegetation (Hazevoet area of 6.5 territories/100 ha. The preference for 1995). On São Nicolau, the species formerly coffee plantations interspersed with fruit trees is bred in orange groves and coffee plantations highlighted by the distance between nests with (Bolle 1856; Alexander 1898) as well as in culti- broods; the minimum distance between occu- vated sugar cane (Keulemans 1866); now it pied nests in such areas was just 30 m.