In general terms, scientists have a clear idea about what snakes eat, according to Bryan Maritz, senior lecturer at the Department of Biodiversity & Conservation Biology at the University of the Western Cape. For example, one rule of thumb is that there are no vegetarian snakes, since no species of snake eat any plant material at all, and every snake on the planet is a predator of other animals.
What other animals they’re eating, though, ranges enormously depending on species, geography, time of year and more. “In terms of the details of what individual species eat, we have relatively limited information for most species,” says Maritz.
Some snakes prefer to eat amphibians, like frogs and arthropods, like spiders, or everything from ant and termite eggs to soft-bodied earthworms. Others prefer mammals, like mice, all the way up to antelope — think about giant snakes like pythons and anacondas and how they can eat huge things, including people. And then some like to eat birds.
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Yes, Some Snakes Love Snacking on Birds
Given how varied the snake diet is, out of the over 4,000 species of snakes worldwide, there are several snakes that like to make birds a staple in their diet. Whilst there are species that predominantly eat birds, no snake only eats a diet of birds, according to Maritz, as it's rare to have genuine specialization on a single prey.
“I would guess, the single biggest predictor of whether you can eat birds is body size,” says Maritz.
In fact, the consumption of adult birds is relatively rare. There are some species that like the taste of adult birds, but they’re generally the larger-bodied snakes — such as kingsnakes — supposedly because of the physical constraints of swallowing a bird.
“Bear in mind that snakes are swallowing their prey whole,” says Maritz. “Birds have got wings that stick out in weird ways that are problematic. They are relatively round, stout animals, they've got all these extra fluffy feathers everywhere that are not providing any nutritional value.”
Most species of snakes prefer to go for chicks or bird eggs instead, as they’re easier to get a hold of and munch down on. Not only are they smaller and easier to swallow whole, they’re also less likely to fight back, especially the eggs.
Snakes also sometimes change their diet as they age: when they’re small, they start off by eating amphibians and reptiles, then as they get bigger, there’s an inclusion of more endothermic prey such as mammals and birds.
How Snakes Kill a Bird
Eating birds is common both for non-venomous snakes and venomous ones, and various different types of venoms can be effective for immobilizing a bird: be it toxin cocktails that tackle the body’s circulatory system, or the body’s nervous system, for instance.
What’s more, snacking on some bird-nugget is something both tree-climbing snakes and ground-dwelling ones seem to fancy. Birds occupy both these environments, which makes it convenient for different species of snakes that like to hunt in different ways.
“It's not a clean-cut one or the other, we tend to think of it as a continuum,” says Maritz.
Some species are more active foragers, and they search around their environment and try to find cues of their prey to then snatch it — whip snakes, garter snakes, and some species of rat snakes like to play this hunting game. They might actively raid nests both on the ground and in trees, for example. Other snake species might sit still and wait for prey to pass them, and then reach out and grab them. That’s the case for some of the Asian Vipers or American rattlesnakes, or pythons and boas.
The Tale of the Common Egg-Eater
“There are, however, species that exclusively eat a diet of bird eggs,” says Maritz. He’s thinking of a species of African dasypeltis, also known as the common egg eater. “Dasypeltis are these just outrageous snakes.”
This is how they do it. First, they move around the landscape, find a nest, and grab an egg. Then, they swallow it into their throat without cracking it, because they have basically toothless jaws, and they press it with their throat against several protuberances off the back of their vertebral column, which causes that egg to crack. Finally, they drink down the contents and regurgitate the eggshells.
“It’s this really, really cool system,” says Maritz, a system that has also been studied in the Indian egg-eating snake (Elachistodon westermanni), which is ecologically similar. Various rat snakes are also known for eating a bunch of bird eggs, as are bull snakes, kingsnakes, and eastern racers.
The Tale of the Spider-Tailed Horned Viper
The spider-tailed horned viper (Pseudocerastes urarachnoides) is a species endemic to the Middle East, namely parts of Iran and Iraq. It is not particularly well known, according to Maritz, having first been officially described just in 2006.
But its neat predatory system is one that has birds tremoring. These vipers do what is known as “caudal luring”, which is essentially when snakes mimic something interesting to their prey by moving their tails. For instance, the spider-tailed viper uses its spider-like tail to lure in birds, which in turn fly in to attack what looks like a delicious snack and are caught with a bad surprise.
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Delicious Birds in the Desert
In the South African Kalahari Desert, with its mostly open, arid landscape, big trees are often home to giant communal Weaver bird nests. Weaver birds are also known as “sociable weavers” because their nests — which have upward of hundreds of chambers — act as a breeding spot for them to return to each year and can host colonies of 600 to 700 birds.
Cape cobras in the Kalahari Desert climb up these trees, maintain a grip with their bodies, and then use their sense of smell to track down which chambers host the eggs and chicks, mainly raiding their nests when it is breeding season.
“They're utilizing these birds as a really important resource as part of their diet when they're available. And importantly, they're only available after really good rains,” says Maritz. “For weavers, snakes are certainly the primary determinant of whether those birds successfully breed or not.”