Raso Skylark

Raso larks are relatively small in size. The Raso larks can range from sizes between 14 and 18 cm. The adult population is mostly made up of males who are larger than the females. The body has black and brown short streaks and paler around the chest with an erectile crest. The bill is thick-based and robust, longer for the males. The Raso lark is considered an adult when it has developed a reddish-brown tone between the ears and tail, with a pattern on the crown and back. While in flight they display a short tail with short broad wings. The tail and edge of the wings are white.

The Raso lark is restricted in range to only Raso islet in the Cape Verde archipelago, although historically it is believed to have ranged over two other islands, Branco and São Vicente Island. All three of these islands were joined in the last ice age. Evidence from subfossil bone deposits reveal that the Raso lark once also existed on the islands of Santa Luzia, São Vicente, Santo Antão, and possibly Branco during the glacial times, before human colonization in the 15th century. Unfortunately, colonization was followed by a rapid extinction of local fauna. Raso islet itself has no permanent water and has never been inhabited by people, a fact that has probably saved the lark from extinction until now. The island consists mostly of rocky desert with sandy parts in the west. Most Raso larks are found on level plains with volcanic soil and are associated with small vegetated patches along dry stream beds in which it feeds and breeds. Suitable breeding grounds on the island of Raso cover less than half of the island. The barren island suffers from frequent droughts which create dry plains that force the Raso larks to move across the island in search for food. Their most common areas of habitation are near dry river beds, but due to the scarcity of water, only patches of vegetation remain for Raso larks to reside in. …

A number of desert-dwelling larks have evolved long bills to aid in digging for food in the sandy environment but the enlarged bill of the Raso lark has evolved for dominance displays among males. Flocks have also been observed feeding among rocks close to the sea, and the birds excavate holes in sandy soil to extract the small bulbs of nutsedges, which are perennial weeds in the sedge family that superficially resemble grasses.

Breeding. Breeding is very unpredictable, as it is dependent on the occurrence of rain. Courtship behaviour is similar to that of the Eurasian skylark. The male courts the female by singing softly, raising its chest, and hopping up and down while the wings are spread open. Once done mating, both the male and female collect dried grass in order to build a nest. The male defends the nesting site while the female finds a safe location to build a nest. The female Raso lark lays one to three eggs per clutch, usually a day apart. The incubation time is thought to be 15 days. During incubation the female sits on the eggs for ten-minute intervals and then goes off to find food. The Raso lark population changes rapidly in response to rain, and has fallen to extremely low levels during droughts (Ratcliffe et al. 1999, Donald et al. 2003, Donald and Brooke 2006). …