Vampire ground finch

The vampire finch is sexually dimorphic as typical for its genus, with the males being primarily black and the females grey with brown streaks. It has a lilting song along with a drawn-out, buzzing call on Wolf, a buzzing song on Darwin, and whistling calls on both islands.^[2]

This bird is most famous for its unusual diet. When alternative sources are scarce, the vampire finch occasionally feeds by drinking the blood of other birds, chiefly the Nazca and blue-footed boobies, pecking at their skin with their sharp beaks until blood is drawn.^[5][6] The boobies do not offer much resistance against this behavior. It has been theorized that this behavior evolved from the pecking behavior that the finch used to clean parasites from the plumage of the booby.^[7] Typically the boobies do not fight back because the interaction is relatively harmless for them and not worth abandoning their nest over. ^[8] Another reason for not fighting back is that the finches sometimes swarm in multiples which makes it impractical for the single booby to defend itself.^[9] The finches also feed on eggs, stealing them just after they are laid and rolling them (by pushing with their legs and using their beak as a pivot) into rocks until they break. Guano and leftover fish from other predators additionally serve as diet options.^[6]

Vampire ground finches drink more blood during dry seasons when seeds and other prey are scarce, resuming omnivory when the rainy season begins. There were also significant variations in the intestinal microbial community structure between species, with a clear separation between vampire ground finches and other finches. Vampire ground finches have intestinal microbial communities rich in peptostreptococcaceae, similar to vampire bats.^[10]

More conventionally for birds, but still unusual among Geospiza, they also take nectar from Galápagos prickly pear (Opuntia echios var. gigantea) flowers, at least on Wolf Island.^[5] The reason for these peculiar feeding habits is the lack of fresh water on these birds' home islands. Nonetheless, the mainstay of their diet is made up of seeds and invertebrates, like other members of their genus.^[5]

The vampire finch is classified as vulnerable by the IUCN based on its very restricted distribution and the impact of invasive species in its habitat.^[1] Conservation efforts that affect the vampire ground finch typically fall under ecosystem wide protection efforts of all of Darwin's finches on the Galápagos Islands, since all of these finches live in similar habitats and face similar problems often introduced by humans such as invasive parasites, newly introduced predators like cats, climate pressures, and habitat disturbances.^[11]

It is approximated that fewer than 1,000 individuals of the Vampire ground finch are endemic to the Wolf and Darwin islands of the Galápagos. This isolated population makes it vulnerable to potential threats such as the invasive avian vampire fly (Philornis downsi) and viruses like the avian pox.^[12] Originally spotted in the Galápagos in 1964, the avian vampire fly targets nests of Darwin's finches with their parasitic larvae. The avian vampire fly plants their larvae inside of the chicks' nares so that they can feed on the blood and tissues of the chicks, often leading to the nestlings' deaths.^[13] So far there have only been recorded instances of this happening to Darwin's finches on the Santa Cruz island of the Galápagos which is not inhibited by the vampire ground finch.^[14]