Critically Endangered lark rebounds after reintroduction success
Until recently, the entire global population of Raso Lark Alauda razae was confined to Raso islet, a small volcanic island in the Barlavento archipelago of Cabo Verde. On the islet, this little passerine bird had just 4 km2 of suitable area for breeding. Rain is very important for this bird: it depends on rainfall to get enough food to breed. During droughts lasting as long as several years, the Raso Lark population decreased drastically, touching the limits of extinction. By contrast, when the population was at its upper limit, the island was close to seeming flooded.
In the past 17 years, the Raso Lark population has fluctuated between 1550 and just 60 birds. Urgent action was needed for this Critically Endangered species and in 2018, a team comprising Biosfera (Cabo Verdean NGO), SPEA (the Portuguese Society for the Study of Birds, BirdLife Partner), and DNA (Cabo Verde’s environmental agency) with the support of the Raso Lark expert Dr Mike Brooke, decided to translocate (in other words, “move”) some birds to the neighbouring larger island of Santa Luzia in order to re-establish a new population of the species there.
Raso Lark, copyright Paul Donald, from the surfbirds galleries
Santa Luzia, an uninhabited island in Cabo Verde, was the chosen location due to its proximity to Raso islet, the presence of similar habitats, and the sub-fossil evidence that confirmed the presence of the species in the past.
After the abandonment of colonization attempts centuries ago, threats to the Raso Lark such as human activities and cattle trampling disappeared; but the presence of invasive alien species – feral cats and mice – still presented a major threat preventing a successful translocation (or in this case, a late reintroduction). As a ground-nester, the Raso Lark is highly at risk from invasive predators.
The ground-breaking reintroduction took place in April 2018, and a total of 37 birds, 25 males and 12 females were moved to two distinct locations previously identified in Santa Luzia. All the translocated birds were colour ringed, and monitored monthly to detect fluctuation changes and check how they adapted to their new environment. In late August 2018, a recently fledged bird was found being fed, thereby confirming the very first Raso Lark breeding on Santa Luzia!
Later in the year, the team recorded independent movements of other larks crossing from Raso to Santa Luzia, as well as others returning to the population source in Raso; confirming for the first time that the species travelled between the islands. Some other unmarked birds were sighted in Santa Luzia that could either have originated from Raso, or be other juveniles born locally.
By March 2019, the number of Raso larks on Santa Luzia was about 20: five from the original translocation, two other colour-ringed females that had flown themselves from Raso to Santa Luzia, and twelve unmarked birds. This last group included birds raised on Santa Luzia and, very possibly, other non-ringed birds that had flown from Raso to Santa Luzia. Although the Santa Luzia population seemed well established, the team decided to bring 33 more birds (19 males and 14 females) from Raso to Santa Luzia to boost the population and increase the chances of success.
After a very dry rainy season in 2019, we only found a single nest with a chick in Santa Luzia. This confirmed reproduction on the island, but at a very slow pace. By the end of the year, Santa Luzia’s Raso Lark population was estimated to be at around 40 birds. At that point in time, there were still some feral cats roaming on the island, although in much smaller numbers than the year before.
Checking in on the Raso Larks in 2020
The first preliminary population assessment in February 2020 was worrisome: abundant signs of feral cat were detected in the main area where the larks bred and fed, and not many birds were seen. Then, due to the travel restrictions related with the COVID-19 pandemic, monitoring was halted for more than six months.
It turns out the year 2020 also has some upsides, though. In October 2020 the team received amazing news: seven breeding pairs with 17 juveniles had been detected on Santa Luzia! Cabo Verde finally had a good rainy season, which caused an increase in the Raso Lark’s food resources. And in early November, they found a second laying: four nests with seven chicks were found in the northern area, all of them near their old nest. These results confirm the translocation’s success, and give hopes of a bright future for the Raso Lark – now officially a multi-island species again.
Dealing with invasive species
The project’s invasive species management measures seem to be producing results; the team haven’t registered any sign of feral cats since August. The mice population density is also very low, contributing to a successful breeding season for several native species:
- The Bar-tailed Lark Ammomanes cincture is now widespread around the island, contrasting with the few pairs estimated at the beginning of the project;
- Species such as the Cream-coloured Courser Cursorius cursor or the Common Quail Coturnix coturnix are sighted more frequently;
- Terrestrial reptile populations (Geckos and Skinks) are increasing and many juveniles are observed regularly all over the island;
- For the first time, not a single newly hatched turtle was attacked by cats.