I have slowly been reading Bram Stoker’s Dracula over the past few months through Dracula Daily (it’s a great site that emails you parts of Dracula on the day they occurred in the novel). If you haven’t read Dracula, I highly recommend it. It’s a pretty good read!
Because of Dracula, I’ve been thinking a lot about vampires lately. Which of course led me to think about real-life vampires. I’d heard of vampire bats and insects like mosquitos and ticks, but were there other animals that drink blood?
It turns out there are.
Say hello to the vampire ground finch, or simply the vampire finch (Geospiza septentrionalis).
This little bird is one of Darwin’s finches, the group of about 13 species of birds that live on the Galápagos Islands and that played a critical role in Darwin coming up with his theory of evolution by natural selection. After their ancestor species arrived to the island, Darwin’s finches evolved into separate species that were adapted to the unique environment of the particular island they lived on. The birds also evolved different types of bills so that each species could specialize in a particular type of food (like seeds or insects).
This evolutionary divergence may still be going on. The vampire finch was only relatively recently considered to be a separate species from the sharp-beaked ground finch. However, the International Ornithologist’s Union has split the vampire finch from the sharp-beaked ground finch based on both genetics and differences in song between the two species.
Life in the Galápagos
The vampire finch lives a pretty isolated life in the Galápagos – they are found only on two tiny islands in the archipelago, Darwin Island and Wolf Island. These islands are remote even by Galápagos standards, and basically no humans except from the occasional scientist or diver really go there. In fact, the first visit to Darwin Island wasn’t until 1964 and only occurred with the help of a helicopter.
The two islands are also far from each other. Darwin Island is about 21 km (13 miles) north of Wolf Island. This separation may have led to slight differences in vampire finch song across the islands. While vampire finches on both islands have a whistling call, only the vampire finches on Wolf Island appear to make a buzzing call. In addition, Wolf Island vampire finches have a more melodious song while Darwin Island vampire finches have a more buzzing song.
Yes, they drink (bird) blood
Vampire finches have a relatively diverse diet. The bulk of what they eat are seeds and insects – their sharp beak may have originally evolved to eat insects. They’ll also eat nectar from Galápagos prickly pear flowers.
But in an action pretty rare among birds, vampire finches also eat (you guessed it) blood. To be fair, blood is not the preferred food source of vampire finches – they seem to only drink it when seeds and insects are less abundant. Scientists also think vampire finches started drinking blood as a way to stay hydrated on the dry and arid Darwin and Wolf Islands. You gotta drink something when it hasn’t rained and there’s no permanent source of water around.
Where did this blood-drinking behavior come from? We aren’t totally sure, but the theory is that it evolved from the habit of picking parasites from other birds. You see, some birds are helpful and will pick parasites like ticks off of others – the larger bird gets freedom from parasites, and the helpers get a free meal. It’s a win-win!
At some point, though, vampire finches decided to skip the parasite middle man and go straight to drinking blood from the source. They will peck at the base of feathers of large seabirds like Nazca boobies and red-footed boobies until the bird starts to bleed. Then it’s simply a matter of lapping up the flowing blood.
Do the boobies mind? I mean, it’s probably not very pleasant to get pecked at and have your blood drunk. But the boobies still seem to tolerate it – it’s probably like us getting bit by mosquitos. If the boobies get really annoyed, they’ll simply fly off and leave the vampire finches behind.
Vampire finches don’t stop at drinking booby blood, though – they’ll also go after booby eggs when they get a chance. The finches will steal the eggs from the nest right after they are laid. To crack them, the vampire finches will roll the eggs into rocks using their beak as a pivot and pushing with their legs. Once the eggs break, the vampire finch can drink all the liquid inside.
Gut Bacteria
Of course, not every animal can have a diet like a vampire finch. Blood is high in salt and iron, but low in essential nutrients like B vitamins. To stay healthy, vampire finches only drink blood when they have no water to drink and seeds and insects are scarce.
They are also adapted to blood-drinking and have a specific set of bacteria in their gut. Your gut microbiome is made of all the microbes that live inside your gut; it plays an important role in our digestion and may impact other behaviors. Your microbiome also plays a role in what you eat, since different bacteria can break down different types of food.
Now, most of Darwin’s finches have a very similar microbiome, which is a little surprising given that they live on different islands and eat different types of food. The microbiome of the vampire finch, though, is extra special. A 2018 study found that their microbiome had bacteria not found in any other of the Darwin’s finches. Some of the bacteria in the vampire finches were ones usually found in carnivorous birds and mammals
A 2019 study looked closer at the vampire finch microbiome and compared it to vampire bats. Although they weren’t super similar, the researchers did find one bacteria in common: Peptostreptococcaceae. This bacteria may be important for blood-drinking species, since it seems to help animals process salt and iron (you know, the stuff that is found in high amounts in blood).
Vampire flies
Unfortunately for the vampire finches, they aren’t the only vampire in the Galápagos – an invasive species of botfly called the ‘avian vampire fly’ has been wrecking havoc on finches throughout the archipelagos. While the adults are fruit- and nectar-eaters, the avian vampire larvae eat (you guessed it) blood. Adults will lay eggs in the nests of birds; when the eggs hatch, the larvae parasitize the young chicks and feed on their blood and tissue. Unfortunately, this can kill the young birds.
But there is hope! One solution for the invasion of the vampire fly is to help the finches help themselves with insecticide-infused cotton. This insecticide can kill the flies without harming the chicks. If finches are offered cotton with the insecticide, they can use it as a nesting material and kill 100% of the fly larvae in their nest.
Now, I normally think that humans should leave nature along and not meddle in the affairs of animals. HOWEVER, I make an exception for invasive species. Invasive species can wreck havoc on local ecosystems because the native plants and animals do not have any defenses to deal with the invaders. In addition, humans are usually the reason an invasive species made it to a new location; we should be the ones to help get rid of them.
With the help of some cotton, hopefully the vampire finches will stick around for a long time.
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