Komodo dragons are an astonishing sight, their intimidating size only augmented by their venomous bites and keen hunting abilities. Capable of long-distance travel and dominating most other animals, some have wondered why they aren’t more widespread.
It turns out that these human-sized lizards are perfectly content to stay close to home, rarely—if ever—venturing outside of the valleys they hatched in, according to new research.
A study published this week in Proceedings B of the Royal Society is the product of a decade of observations of the reptiles’ movement patterns in the only place on Earth these animals reside: a handful of craggy islands in Indonesia’s Lesser Sunda archipelago.
The paper found these animals are highly mobile and athletic, sometimes moving up to seven miles per day in their native valleys. "They're really active by lizard standards,” says Tim Jessop, an ecologist at Deakins University in Australia, and lead author on the study.
But they’re apparently just homebodies.
In a given day they shuffle within the confines of their home valley, with ranges of over a mile in width. There, they pace between dry woodlands and sun-broiled, rocky grasslands, sniffing out prey or other dragons—which can sometimes be one in the same.
Jessop, alongside other researchers with the Komodo Survival Program—a non-profit organization devoted to scientific monitoring and management of dragon populations, investigated Komodo dragon movements as part of an ongoing, long-term conservation project.
The team studied dragons at ten different sites throughout Komodo National Park, tracking their movements using GPS or radio collars, or by trapping, marking, and recapturing them. They also took seven dragons and relocated them to different parts of their island—or even a different island altogether—to see how they adjusted.
Despite bouncing all over the valleys the dragons were either born in or first captured in, the lizards almost never left the area. Over one thousand Komodo dragons that were recaptured, only two had migrated between sites.
This homebound inertia appears to be relatively intentional, rather than being mere sluggishness or a poor sense of direction. For example, the dragons that were relocated miles away—to the opposite end of their home island, for instance—found their way homes over the course of a few months.
But when the dragons found themselves separated from their home island by a thin stretch of ocean, only a quick swim away, they settled in.
The water itself isn’t the problem, since Komodo dragons can swim pretty well. Instead, Jessop thinks that traversing open ocean introduces quite a bit of risk—something the dragons may be avoiding.
The Lesser Sunda Islands are braided with strong currents, which could easily carry a dragon out to sea. But even being pushed to another island could be disastrous, since food resources and mate quality can vary wildly between islands.
Arriving on a small, food-depleted spit of land as a large adult dragon could be a death sentence, so it might be advantageous be sedentary. Indeed, during the ten-year study, only two dragons were spotted in open water.
This may carry over to inter-valley travel too, where introducing uncertainty may be so costly that it’s worth risking inbreeding. The researchers found evidence in the dragons’ DNA that the animals are becoming somewhat inbred. This can become especially problematic if overlap between populations is cut off when populations decline through hunting or habitat loss.
“The study is an important contribution to our understanding of Komodo dragon biology and our knowledge of lizards in general,” says Mozes Blom, an evolutionary biologist at Museum für Naturkunde Berlin who was not involved in this study. “We have very little understanding of how lizards and snakes have spread across continents and oceans and what motivates them to migrate.”
Jim McGuire, a biologist at the University of California, Berkeley also not involved with this study, notes that the dragons’ aversion to migration is particularly interesting given that tens of thousands of years ago, the species was found throughout a much wider territory in the Indo-Australian region. It’s unclear if the dragons’ behavior may have recently changed—or if some other factor explains the contracted size.
Either way, the realization that Komodo dragons are currently unwilling to move around is crucial knowledge for conservation efforts. The animals may not be able to quickly recover after population declines or colonize new areas, for example.
If conservationists can anticipate that there’s no self-driven, spontaneous wandering of individual dragons across whole islands, they can more accurately envision an effective conservation strategy for the reptiles. Though, the lack of movement doesn’t exactly make it easy on the dragons’ chances of long-term survival.
“Lack of dispersal has probably worked really well for Komodo dragons over millennia,” says Jessop, but with climate change, sea-level rise, and human threats like poaching, it may hurt more than help.