Relentless, blood-sucking... finches?

Animals have always found purposes (also known as niches) in their environments and filled them in ways that seem incomprehensible; adapting their body almost perfectly to fill the said niche. A place that is a niche within itself is the Galapagos islands- remote, volcanic, biodiverse hotspots that call for an ‘adapt or die’ lifestyle for the animals that inhabit them. Darwin’s finches demonstrated this with their beaks perfectly adapting to exploit a change in their food source. A finch I was previously unaware of was introduced to me through Sir David Attenborough in his recent BBC series ‘Perfect Planet’ (well worth a watch) and their enigmatic nature fascinated me- so naturally, I had to share.

These finches are known as vampire finches and their name sums them up pretty well. They live on two of the most remote and northern islands of the Galapagos- Wolf and Darwin- where food and fresh water is scarce, and their only companions on the islands are the red-footed and Nazca boobies. It is thought that years ago the finches used to feed solely off parasites that lived on the boobies as a food source, creating a mutually beneficial, symbiotic relationship for the two- the boobies had a free parasite-removal team and the finches got access to a food source that wasn’t seasonally dependent. After parasitic removal, the boobies are often left with open skin lesions, which to one ground finch (the believed ancestor of the vampire finch), seemed too good of an opportunity to turn up. This was an easy, open route for the consumption of a new, highly nutritious food source-blood. But, this new exploitative habit of the finches had to remain unnoticed to ensure the upkeep of the trusting relationship they shared with the boobies. Over time these finches with sharper beaks and other adaptions survived more and reproduced more, in true natural selection style. It’s assumed that the boobies do not feel much pain and can live without the small amount of blood the finches take. The finches are benefited also; by only taking a small amount they have continual access and don’t break the now partially parasitic relationship they have with the boobies. It is believed many finches still eat parasites off the boobies and that the blood only makes up for 10% of their diet [1].

What amazes me most about this adaption is that it is not just a long, sharp beak these finches have- they now possess a whole range of tools to optimise their newly found vampirism. These fine-tuned tools include blood crops in their throat to collect the blood (as seen in the photo below) [1]. Another tool under their belt includes blood-digesting microbes found in their gut, a massive difference to microbiome observed in Darwin’s finches [1]. Even the behaviour of these birds has evolved and become parasitic in nature. The birds are thinking and acting like the parasites they once consumed, whereby they take just enough blood to ensure a meal but without causing damage to their host. Some believed these blood-suckers have mastered a perfect equilibrium, whereby they may bother the boobies slightly, it’s rarely enough to cause these boobies to react in aggression and provoke them to fly away. Some suggest that putting up a fight isn’t worthwhile for the boobies, especially if caring for their young. These critters never seem to kill and once they swarm you, your defence is futile [2].

Image taken by Daniel Baldassarre, 2021.

Blood isn’t all that’s on the menu for these tiny monsters. They also will find and roll eggs to crack to enjoy the yolk, drink up other birds’ vomit, and using their beak for the ground finches’ original purpose- piercing fruits for their juices, seeds and flesh [2]. Many call these birds ‘enterprisers’, finding a unique way to thrive off the unforgiving conditions of these islands- and I can see why.

These birds and everything they have become highlights how animals can adapt and change almost everything about themselves to fit a niche in an environment. It seems the harsher the environment is on the survival of an animal, the more extreme lengths, in terms of evolution, it will go to in order to survive- what could these animals become? I truly believe animals could evolve in any environment and will always outlive humans as their ability and desire to survive is much better than ours.