Data Zone
Justification of Red List category
This species is confined to one very small island, where its population fluctuates in response to rainfall and appears to reach extremely small numbers. Climate change may increase drought in Cabo Verde, adding to the likelihood of extinction. As a ground-nester, the species is highly at risk from the accidental introduction of predators. For all of these reasons, it is classified as Critically Endangered.
Population justification
The population was estimated at 1,558 individuals in November 2011, before it declined to 855 in November 2015 (M. Brooke in litt. 2016). This equates roughly to 570 mature individuals. However, when the population is smaller it can be strongly male-biased, meaning the effective population size is smaller than it first appears (M. Brooke in litt. 2008, 2010, Brooke et al. 2010). Therefore, the population is placed in the band 250-999 mature individuals.
Trend justification
The population undergoes fluctuations due to varying rainfall levels on Raso (Donald et al. 2003, Donald and Brooke 2006, Brooke et al. 2012). It has increased rapidly since 2004, but it is uncertain whether this relates to a temporary fluctuation or a longer-term increase.
Alauda razae is restricted to the very small (7 km2), arid, uninhabited island of Raso in the Cabo Verde Islands, although evidence from sub-fossil bone deposits suggests that the species also occurred on Santa Luzia, São Vicente and Santo Antão prior to human colonisation in the 15th century, after which extinction on these islands appears to have been rapid (Mateo et al. 2009). It is likely that the species also occurred on Branco, which formed a single island with São Vicente, Santa Luzia and Raso during the last glacial low 18,000 years BP. Suitable breeding habitat covers less than half the area of Raso. The lark's population is believed to fluctuate in response to climate and continues to do so. From the mid 1960s to the early 1980s the population was estimated at only 20-50 pairs (Ratcliffe et al. 1999). In early 1985, however, a survey showed at least 150 birds to be present. Subsequent day visits resulted in the following estimates: 75-100 pairs in early 1986 and early 1988, c.250 birds in late 1988, c.200 birds in early 1989, c.250 birds in early 1990 and 1992. Complete censuses of the island in 1998 and 2003 found 92 and 98 birds respectively, restricted to the south and west of the islet (Ratcliffe et al. 1999, P. Donald in litt. 2003), but following rain in 2004 the population rapidly increased to 130 individuals in 2005 (Donald and Brooke 2006), 190 in November 2009 (M. Brooke in litt. 2008, 2010), and 1,558 in November 2011, before declining again to 855 in November 2015 (M. Brooke in litt. 2016). In November 2016, 908 individuals were recorded, in November 2017, there were 1,514 (Brooke, 2018), while in November 2019, the population on Raso was c.1,100 (M. Brooke pers. comm., 2020).
When the population is small, only a third of the birds are female (P. Donald in litt. 2003, Donald and Brooke 2006). A single bird near Ponta do Barril on the island of São Nicolau in March 2009 was previously the only record away from Raso (Hazevoet 2012), and it most likely represented a wandering bird from Raso. However, in 2018, 25 males and 12 females were translocated from Raso to Santa Luzia (Brooke et al., 2018). By 2019, there were 20 birds on Santa Luzia, comprising of 5 from the original translocation, birds raised on Santa Luzia, two ringed females that flew over independently from Raso, and other unringed birds suspected of doing the same. In April 2019, a further 19 males and 14 females were translocated to Santa Luzia (Brooke et al., 2019).
The species is found on level plains with volcanic soil and is associated with small vegetated patches along dry stream beds in which it feeds and breeds (Ratcliffe et al. 1999). There is a significant difference in bill size between males and females, enabling the species to exploit limited food resources, with both sexes having relatively larger bills than congeners (Donald et al. 2003, Donald and Brooke 2006). A number of desert-dwelling larks have evolved long bills, apparently to aid digging for food in a sandy environment (Donald and Brooke 2006). Flocks have also been observed feeding among rocks close to the sea, and the birds (particularly males) excavate holes in sandy soil to extract the small bulbs of nutsedges Cyperus bulbosus or C. cadamosti (Donald and Brooke 2006). Breeding is erratic and governed by the slight and irregular rains (Hazevoet 1995, Donald et al. 2003). The population changes rapidly in response to rain, which is a prerequisite for breeding, and has fallen to extremely low levels during droughts (Ratcliffe et al. 1999, Donald et al. 2003, Donald and Brooke 2006). At times the population has been strongly male-biased (P. Donald in litt. 2003, M. Brooke in litt. 2008, 2010, 2012). During the non-breeding season, birds aggregate into flocks (Donald and Brooke 2006) and can be found in other parts of the island. Adult survival is high, particularly during wetter years (Dierickx et al., 2019) and the species is thought to be relatively long-lived (Brooke et al. 2012). Breeding success is sometimes very low, due to high predation by the near-endemic gecko Tarentola gigas. The record from São Nicolau in March 2009 (Hazevoet 2012) perhaps indicates that the species has some limited dispersal capability.
Drought over successive breeding seasons reduces the population. Given the species's sensitivity to drought, long-term desertification in the Cape Verdes is clearly a major threat (Ratcliffe et al. 1999). In addition, nest predation (probably by a near-endemic gecko) is high in some years (Donald et al. 2003). Ground-nesting makes the species extremely vulnerable to the potential accidental introduction of rats, cats and dogs brought to the island by fishers (C. J. Hazevoet in litt. 1995). The danger of such introductions (and the potential impact of non-native plant introductions) is now exacerbated by increased tourist activity in the Cape Verde Islands. Evidence of cats (Ratcliffe et al. 1999, Donald et al. 2003) and dogs (Donald et al. 2003) on the island was found during surveys in 1998 and 2001 but these populations did not establish themselves and the island is currently mammal-free. Global climate change is likely to threaten this highly-restricted and precipitation-dependent species.
Conservation Actions Underway
Raso Lark has been officially protected under Cape Verde law since 1955 (Donald et al. 2003). In 1990, Raso was declared a national park (Hazevoet 1995). To date, there has been limited enforcement of these laws on the ground (Hazevoet 1999). Surveys have revealed the absence of cats on the island. Annual population monitoring has been carried out since 2001, and future research is planned to understand the conditions needed to enable successful breeding (M. Brooke in litt. 2008, 2010). In 2018, 37 birds were translocated from Raso to Santa Luzia (Brooke et al., 2018). The MAVA eradication programme reduced the number of cats on Santa Luzia to <10 by early 2019, so a further 33 larks were translocated in 2019 (Brooke et al., 2019).
18 cm. Small, heavy-billed lark. Thick-based heavy bill, particularly in males, imparts an upturned appearance. Body plumage heavily streaked with buff and black, short erectile crest. Heavily streaked on breast, paler underparts. Voice Described as similar to Common Skylark A. arvensis, given both from the ground and in display-flight.
Text account compilers
Clark, J.
Contributors
Benstead, P., Bird, J., Brooke, M., Donald, P., Ekstrom, J., Hazevoet, C., Hermes, C., Martin, R., Shutes, S., Symes, A., Taylor, J. & Westrip, J.R.S.
Recommended citation
BirdLife International (2024) Species factsheet: Raso Lark Alauda razae. Downloaded from
https://datazone.birdlife.org/species/factsheet/raso-lark-alauda-razae 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.