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Because their relative isolation encourages speciation, oceanic islands are hotspots of biodiversity. Yet their relatively small size, atypically defenseless animals and plants, and ecological vulnerability to the effects of introduced species has also made them hotspots of extinction.

Jairo Patiño, José María Fernández-Palacios and colleagues chronicle every known terrestrial extinction in Macaronesia—an area in the Atlantic Ocean comprising the volcanic archipelagos of the Azores, Madeira, Selvagens, the Canaries, and Cabo Verde. The work is in PNAS Nexus.

The survey uncovered 220 extinctions representing 3.1% of the Macaronesian endemic species, of which 111 were land snails, 55 were arthropods, 27 were birds, and 15 were reptiles—including several species of giant tortoises. Half of the endemic birds of these islands are now extinct. Plants fared better, and lichen and fungi saw no recorded extinctions—although that result is likely influenced by a lack of records for these taxa.

Of the 220 extinctions, half are clearly associated with human arrival—particularly the arrival of the Portuguese and Castilian colonists and their domestic animals in the 15th century. Some extinctions were likely related to climatic changes or volcanic events before human arrival, but the rate of extinctions in the post-human period is more than 12 times higher than the rate before humans arrived.

Extinct birds include the São Jorge rail (Rallus nanus) from São Jorge Island in the Azores; the Madeiran Scops Owl (Otus mauli) from Madeira Island; the slender billed greenfinch (Chloris aurelioi) from Tenerife in the Canary Islands; and the São Vicente Quail (Coturnix centensis) from São Vicente Island in Cape Verde. According to the authors, conservation and habitat restoration are imperative to slow the rate of extinction in Macaronesia.

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