Raso Skylark Alauda razae Scientific name definitions

12–13 cm; 18–28 g, male average 24 g, female average 20 g. Small lark with heavy, slightly decurved bill giving front-heavy appearance, relatively short wings (no obvious primary projection), short tail, small erectile crest, strong sexual size dimorphism. Has pale area around eye  (sometimes slightly spectacled appearance), indistinct pale super­cilium; greyish with dull dark streaks above  ; wings and tail darker, blackish, wing-coverts  with pale tips, outer rectrix mostly white; throat white, rest of underparts pale creamy buff (whiter in worn plumage), breast  streaked blackish; bill blue-grey, base of lower mandible whitish; legs dull pinkish. Distinguished from A. arvensis by smaller size, longer and clearly larger bill, greyer plumage lacking rufous tones, in flight no white trailing edge of wing. Sexes alike in plumage; female significantly smaller than male in all measurements, wing average 80 mm (male 87 mm), bill 12·2 mm (male 14·6 mm). Bill length (especially of male) appears to vary seasonally, possibly through wear caused by digging. Juvenile has strong rufous tones, especially on ear-coverts and lower back, pale feather fringes above, breast markings more diffuse; very similar to juvenile A. arvensis.

Raso, in Cape Verde Is.

Found primarily on flat plain of decaying lava, mostly below 50 m. Strongly associated with dry streambeds (ribeiras) and scattered patches of sand, which support low vegetation after rain; also associated with grassy patches along tops of low cliffs on S coast of the island. Occasionally around rock pools at bottom of cliffs. In non-breeding season, a high proportion of population moves to a gravelly valley at E end of island.

Resident; ranges widely during non-breeding season, although distances involved are small. No records away from Raso.

Range of plant and insect species. In analyses of faecal samples of males during breeding season, all contained vegetable matter, c. 50% contained lepidopteran larvae. Other recorded items include seeds, beetles (Coleoptera) and marine gastropods; also takes discarded food scraps. Seen to chase small skinks (Scincus), although whether for food or to keep them away from nests is not known. Forages on ground  . Much feeding involves use of the bill to excavate holes up to 10 cm deep in order to extract bulbs of the nutsedge Cyperus bulbosus; c. 3 minutes of digging required to yield one bulb, although dominant males increase the rate of food intake by displacing digging birds from holes, and in some places vigorously defend a number of holes; in sandy areas, ground sometimes littered with worked-out excavations. In gravel areas, feeds by pecking seeds or invertebrates from ground or from low vegetation, and by turning over small stones; also takes invertebrates, and scraps left by visiting fishermen, around rock pools. Males spend more time in digging than do females, possibly because of sexual differences in bill structure; difference between sexes in feeding strategy may have arisen as a means of partitioning resources in an austere environment. Occasionally drinks seawater from marine rock pools (no standing fresh water exists on Raso).

Male song, in flight or from ground, variations on a liquid “chirr-irr-ipp” or “chirru-dirru”, given in bursts, with frequent intervals sometimes longer than song bursts, recalls that of Galerida cristata; simpler than song of A. arvensis, with more and longer gaps, but song during descent from flight faster, more complex and similar to latter’s. Usual call  “chirr-irr-ipp”, like note of song flight.

Most nesting activity in Oct–Dec, following rainfall (which generally in Sept/Oct), but rain can fall at any time of year and nesting recorded in most months; conversely, long droughts can prevent breeding, sometimes for several successive years. Monogamous; male closely guards mate. Song-flighting male rises vertically to c. 30 m, hovers, descends steeply, singing throughout, display lasting on average 2 minutes, maximum 15 minutes in sample of 150, longest by unpaired males (which defend a territory, once two territories). Nest a deeply grass-lined scrape on ground, similar to that of A. arvensis, often under the low plant Zygophyllum simplex. Clutch 1–3 eggs; incubation by female alone, fed on nest by male, period at least 12 days; nestling period not documented; if nest preyed on, immediately begins a new one, sometimes using lining from original nest. Extremely high rate of nest predation, probably by the near-endemic gecko Tarentola gigas.

CRITICALLY ENDANGERED. Restricted-range species: present in Cape Verde Islands EBA. Has one of the smallest ranges of any bird species, confined to the single uninhabited island of Raso (7 km²), lying c. 20 km W of São Nicolau, in Cape Verde Is. May have been more widely distributed previously, when islands were joined together during periods of lower sea-level. The only lark on Raso. Total population extremely small, fluctuates in relation to rainfall, dropping to as few as ten pairs after prolonged droughts: in Oct 2001 estimated at c. 130 individuals, c. 66% of which males (2 Donald, P.F., de Ponte, M., Pitta Groz, M.J. and Taylor, R. (2003). Status, ecology, behaviour and conservation of Raso Lark Alauda razae. Bird Conservation International. 13: 13-28. Close ); total of 98 birds, only 30 of them females, in Jan 2003 (3 Donald, P.F., Brooke, M. de L., Bolton, M.R., Taylor, R., Wells, C.E., Marlow, T. and Hille, S. (2005). Status of Raso Lark Alauda razae in 21111113, with further notes on sex ratio, behaviour and conservation. Bird Conservation International. 15(2): 165–172. Close ); in 2004 there were 65 individuals, 70% of which males, and in 2008 c. 175 individuals, including juveniles, and 58% of adults were male (4 Brooke, M. de L., Flower, T.P. and Mainwaring, M.C. (2010). A scarcity of females may constrain population growth of threatened bird species: case notes from the Critically Endangered Raso Lark Alauda razae. Bird Conservation International. 20(4): 382–384. Close ). In Nov 2011, population reached 1490 individuals, representing a remarkable twenty-fold increase over seven years, and the highest recorded since the species was discovered (5 Brooke, M. de L., Flower, T.P., Campbell, E.M., Mainwaring, M.C., Davies, S. and Welbergen, J.A. (2012). Rainfall‐related population growth and adult sex ratio change in the Critically Endangered Raso lark (Alauda razae). Animal Conservation. 15(5): 466-471. Close ). Strongly male-dominated sex ratio perhaps explained by differences between males and females in feeding strategy. Despite the very small numbers, densities in favoured areas can be very high. Desertification is greatest threat to the species in the long term, as its population level is determined largely by rainfall. Potential introduction of cats or rats (Rattus) a further serious threat; although cats have been present on Raso in the past, and as recently as late 1990s, they do not appear to have established a breeding population. Development of tourist facilities on nearby São Nicolau and São Vicente is likely to result in increase in numbers of people visiting Raso, with resulting threats of disturbance, trampling and the accidental introduction of mammal predators. Raso is designated a national park, requiring visitors to apply for permission, although this rarely sought. The species is protected under Cape Verde law. Current conservation initiatives  aim to increase capacity of Cape Verde authorities effectively to protect this lark and other important species in the archipelago.