Wildlife Photographer of the Year: blood-loving birds of the Galápagos

By Emily Osterloff

First published 22 October 2018

Wolf Island, in the Galápagos, is remote and rarely visited. But this volcanic island is home to an unusual group of birds: vampire ground finches.

Photographer Thomas P Peschak had the rare opportunity to visit the island and witness the blood-drinking behaviour of these sharp-beaked birds.

'Wolf Island is truly wild,' says Thomas P Peschak, winner of Wildlife Photographer of the Year 2018 in the Behaviour: Birds category.

The isolated island, located in the northwest of the Galápagos archipelago, is often shrouded in mist, its rocky cliffs are exceptionally steep and there is no permanent freshwater source.

'This is a harsh place to survive, unless you are a seabird which can get food from the rich adjacent ocean,' he explains.

But finches are not seabirds and instead of a seafood diet, these small birds have to utilise other resources in their unforgiving environment. Dr Alex Bond, Senior Curator of Birds at the Museum explains the most extreme feeding strategy of all of Darwin's finches.

The vampires of Wolf Island

Nazca boobies (Sula granti) are abundant on Wolf Island (also known as Wenman Island), using it as a breeding ground. They feed by diving at high speed into the surrounding ocean to capture small fishes. When they return to the island, they live in large colonies and nest amongst the dense cactus thickets.

But survival on Wolf Island is tougher for the ground finch species, Geospiza septentrionalis. These small birds are unable to leave the safety of the plateau to find food, but on the island there is no permanent water supply and it rarely rains. This species is also resident on Darwin Island, one of the smallest and the most north-westerly of the Galápagos Islands.  

Galápagos finches are well-known - they are sometimes called Darwin's finches as they were first studied by the famous biologist during his voyage aboard HMS Beagle in the 1830s. Darwin's finches are a group in which each species has specially adapted beaks and behaviours to aid survival in their specific habitats, but are all descendants of a common ancestor.

The finches on Wolf and Darwin islands feed on seeds and insects. But their supply often runs out, especially during the dry season. This leaves them in need of another source of nutrition.

Finches may have once pecked at the feathers of Nazca boobies and other seabirds to feed on parasites, but this trait has developed into one that is unique to G. septentrionalis.

'They have become vampires,' says Thomas. 'I have seen more than half a dozen finches drinking from a single Nazca booby.'

The finches peck at the base of the seabirds' feathers until blood begins to flow, which they then lap up with their tongues. This behaviour has resulted in the common name of vampire ground finches.

The boobies appear tolerant of the vampire birds' behaviour, however. The beak-inflicted wounds and blood loss don't seem to cause the seabirds any significant or lasting damage.

Continued