Vampire finches and oxpecker birds drink blood.

These Adorable Little Birds Will Drink Your Blood

These Adorable Little Birds Will Drink Your Blood

Wild Things
Slate’s animal blog.
Oct. 16 2015 11:10 AM

Vampire Birds Thirst for Blood

A red-billed oxpecker
An oxpecker's relationship with its host is not exactly "mutualistic." The bird is in it for the blood.

Courtesy of Flickr photographer Ian White.

Ticks, leeches, mosquitoes, vampire bats—when it comes to creatures that live by the vein, these are the usual suspects. But what if I told you there was a little blood-slurping birdy more diabolical than all of those guys put together?

Scientists call it Geospiza difficilis, but you can call it the sharp-beaked ground-finch or vampire finch for short.  

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Unlike bald eagles, harpy vultures, horned owls, and all the other big, scary birds that eat meat, the vampire finch looks like an animal that could be found at your backyard feeder. It weighs less than an ounce, has no vivid colorations or vicious talons, and generally just looks like any one of a dozen species flitting across your neighborhood as we speak.

Fortunately for all the birds of suburbia, vampire finches live only on the Galapagos Islands. It’s likely that the remoteness and harshness of this locale are what has driven the birds to draw blood. Their prey is boobies and other large seabirds that may be 50 times the finches’ weight.

“The Galapagos have an environment that fluctuates tremendously, and the birds go through droughts where there’s just not a lot to eat,” explains Ken Petren, an evolutionary ecologist and dean of arts and sciences at the University of Cincinnati.  “And it’s in that context that we see birds being very creative about what they can try to eat.”

Of course, what strikes an evolutionary ecologist as creative, the rest of us would probably call horrific. That’s because the vampire finch isn’t the least bit nice about its bloodletting.

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Vampire bats have teeth so surgically sharp, their victims can sleep through the ordeal. Mosquitoes and ticks anesthetize your skin before they suck. Leeches are aided by the numbing effect of cold water. Some of these bloodsuckers can go unnoticed indefinitely, so polite is their disposition. Who, us? Why, we wouldn’t think of imposing!

But the vampire finch of the Galapagos’ Wolf Island just hops right up onto a blue-footed booby’s back and jams its sharp beak into the seabird’s skin again and again until blood rains down. And once the vein is open, more finches arrive to the party like that blood-rave scene in Blade.

Why the boobies endure the abuse is up for debate. It might be that the boobies have no choice—Petren says Wolf Island has the highest density of vampire finches of any island, thousands and thousands of them in a very small area. It’s also quite far from the rest of the island chain, which means it’s extra remote. Add to that the fact that depending on the time of year, the boobies may be incubating eggs or caring for chicks, both of which the vampires are more than happy to peck at.

Interestingly, because the shells of booby eggs are too strong to penetrate using their beaks, the finches have developed a life hack that affords them yet another food source. Petren says the birds put their beaks on the ground in a sort of headstand, kicking the egg with their feet until it rolls off a cliff and breaks. Add a little Hollandaise and you’ve got Eggs Beelzebub.

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Obviously, I don’t mean to give the impression that vampire finches are in any way evil. They’re simply animals making the best of a bad situation. On a string of islands in the middle of the Pacific, nutrients are hard to come by and an open wound might as well be an oasis.  

After all, the finches of the Galapagos are sort of famous for adapting. There are now more than a dozen finch species on the islands, and each has a special way of surviving. Some eat seeds, others eat insects, and some have devised several different ways to carve up cacti. There’s even a Tim “The Tool Man” Taylor finch that hops around the island grunting and using sticks, cactus spines, and other tools to pry insect larvae and spider eggs out of tree cavities.

Whatever their mode of survival, the finches of the Galapagos have over time developed beaks to match each enterprise. These birds are some of the first and most famous avatars of evolution, which is why they are sometimes called Darwin’s finches.

Vampire finches aren’t even the only blood-drinkers on the Galapagos. The hood mockingbird has also been known to nuzzle into open wounds on boobies and iguanas and ingest the afterbirth of sea lions. There are even records of hood mockingbirds trying to drink from blood dripping down the leg of human researchers.     

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But the Galapagos don’t have a monopoly on bloodthirsty birds. Across the world, on the savannahs of Sub-Saharan Africa, there’s another vampire with an excellent common name—the oxpecker.

Until rather recently, oxpeckers were one of those species held up as an example of mutualism because it was thought that they provide an ecological service to large herbivores by eating their ticks, botfly larvae, and other parasites. The zebra gets rid of all its nasty hitchhikers while the oxpecker gets a fancy dinner full of protein—everybody wins, right?

Well, maybe. And maybe not. One study conducted in the scrubland of Zimbabwe found that cattle allowed to mingle with red-billed oxpeckers did not have significantly fewer ticks than those who had the birds relentlessly shooed away from them. (From the acknowledgements section of the paper: “Phineas Ndlovu, for scaring the oxpeckers.”)

What’s even more interesting, however, is that the paper also noted every pock, scab, and lesion on the cattle during the time of the study. And get this: The cattle that were allowed visits by the oxpeckers not only had a higher proportion of wounds that reopened or failed to heal, but they also had a higher number of wounds overall. This is because oxpeckers are notorious for pick-, pick-, picking their way into their hosts.

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Do a quick YouTube search for oxpeckers, and you’ll find videos of these birds digging into hippo flesh, fighting over buffalo blood, and straddling the head of an antelope just to get at a face wound.

And then there’s this video of a giraffe with more red-billed oxpeckers on him than he has spots. There are birds on his head, neck, chest, back, and legs. Some comb his hair for dead skin and tick nymphs, others pluck off engorged adult parasites. But still more oxpeckers harry an open wound on the giraffe’s chest, dipping their entire heads into the red crevasse.

As the camera pans upwards, we see the bull has a stump where his left ear used to be. The narrator wonders if it isn’t the result of a tick wound opened up and never allowed to heal, thanks to the giraffe’s hungry avian hitchhikers.

No one seems to have observed an oxpecker actually creating a wound, as vampire finches are known to do. But the study mentions watching the birds deliberately peck at the place where a tick was attached to the cow’s skin without any apparent interest in eating the tick itself. It seems likely then that the oxpecker knows it can use a wound created by a parasite to open up a fountain of blood.

So if anyone is still looking for a scary costume this Halloween, I’d encourage you to pass over the werewolves, witches, and bats. Instead, be a little black bird with a beak built for bloodletting. They’ll never see you coming.