This post will soon become available in Spanish

If you haven't seen the incredible footage of the "iguana chase scene" from the BBC's Planet Earth II episode, I encourage you to watch it right away. In addition to being a highly dramatic cinematographic masterpiece, it raises a number of interesting questions about the biology of the snakes in the clip. For a few days after it aired, the Internet was buzzing with these questions, and I've cataloged the answers to some of the most popular ones below. If you have one that isn't listed, feel free to ask it in the comments! And, if you want to know more about the process I used to dig up some of this information, check out my tutorial for teaching oneself about obscure snakes Throughout the clip, Attenborough calls them "racer snakes" 1 , but herpetologists would normally call the snakes on the screen Galápagos Racers. Although these snakes are called "racers", they're not closely related to North American racers (genus); it's been about 45 million years since these two snakes last shared a common ancestor.Galápagos Racers belong to the genusDepending on which sources you consult, there are between 4 and 7 species ofin the Galápagos, as well as one in mainland South America.

Just like Galápagos tortoises, finches, and many other organisms, there are different species of Galápagos Racers on the different Galápagos Islands (one of the concepts that sparked Darwin's theory of evolution by natural selection ).Galápagos. Fernandina has two species of snakes,and. The snakes in the film must be, because they are too large and not boldly banded enough to be. You can read the original descriptions of both species here

Why are there so many of them?

Just as when baby sea turtles emerge from their nests, predators congregate at the temporary buffet, returning afterwards to their usual densities. Around the world, there are numerous examples of avian and snake predators exploiting emerging hatchling iguanas. Researchers working at other iguana nesting sites in the Bahamas , the West Indies, and Venezuela have hypothesized that snakes and other predators also converge on the nesting sites of these other iguanas to exploit the temporary food source. Another example of snakes congregating around abundant prey resources is that of Puerto Rican and Cuban boas, which aggregate around the openings of massive bat caves

The rest of the year, Galápagos Racers eat lava lizards, geckos, insects, marine fishes , and hatchling birds, as well as introduced rats and mice.





Are they really hunting in a pack?









Two P. occidentalis trying to eat the same iguana

Jaw-walking is a fixed action pattern in snakes and they

may eat things that only vaguely resemble their food

once they start jaw-walking them.

From Planet Earth II Behind the Scenes









Why don't the female Marine Iguanas just lay their eggs somewhere else, closer to the ocean maybe?





Studies on the population biology of Marine Iguanas have shown that most of their mortality is caused by "predation, starvation (sometimes as a result of being trapped by a rock), crushing by a rock, being beaten against rocks by the sea, and suffocation in collapsed nest burrows. Animals may also die after being swept out to sea by offshore currents". So, actually, predation may be the best way for them to go. Besides Galápagos Racers, their other predators include Galápagos Hawks, Short-eared Owls, crabs, and Giant Hawk-fish.





Are they venomous/dangerous to humans?





No. Like many snakes, Galápagos Racers are rear-fanged . This means that, although technically they are venomous, they don't pose a danger to humans. Rear-fanged snakes mostly have grooved teeth (rather than hollow fangs) on the back of their upper jaw (as opposed to the front); they can use these teeth to get venom into their prey once they are biting it, but they cannot strike out and deliver venom the way a viper can. A small minority of rear-fanged snakes have delivered medically-significant bites to humans , but almost all of these take place in a captive setting. You can read more about the different types of snake fangs here





I didn't know there were snakes in the Galápagos. How did they get there?





Map showing the estimated age of each of the

Galápagos Islands. From Ali & Aitchison 2014 Galápagos Racers colonized the Galápagos Islands from mainland South America, just like all of the other Galápagos fauna and flora. The modern Galápagos Islands Galápagos Racers colonized the Galápagos Islands from mainland South America, just like all of the other Galápagos fauna and flora. The modern Galápagos Islands formed from volcanoes over the past 4 to 5 million years, although some of them have been building beneath the ocean surface for up to 15 million years. It is thought that there have been islands in the Galápagos for at least 8 million years, but the oldest islands have eroded and are now back beneath the ocean surface.





Because the Galápagos Islands are located only six hundred miles off the coast of Ecuador, it is easier for them to be colonized by plants and animals from the mainland than for a more remote island chain such as Hawaii (which is >2,500 miles away from the nearest snake-inhabited landmass).









Could the film have been staged?





Obviously the scenes are spliced together, but in my opinion there's no chance the Galápagos National Park would allow something like this to be staged. They are among the strictest places in the world for researchers to conduct scientific work. However, more recent episodes of Planet Earth II have been criticized for incorporating fake sound effects











1 This sounds a bit redundant to a snake biologist, but it isn't incorrect. The one thing that I wish BBC programs would do is identify the species in them more precisely. I'm advocating for a "biologist mode" that can be activated which would show the location and identity of species in all clips, similar to the old MTV show Pop-up Video.↩







ACKNOWLEDGMENTS









REFERENCES