What Is Island Tameness? Definition and Examples

It has serious conservation implications.

Feeding On Algae
Marine iguana feeding on an algae covered rock near Fernandina Island, Galapagos.

wildestanimal / Getty Images

Island tameness is a natural phenomenon where animals on remote islands are unafraid of humans, even permitting close contact, because there are little to no predators where they live. Island tameness has been observed in birds, lizards, and several other animals.

This phenomenon poses a serious conservation problem. Populations have declined among many island species because of their poor anti-predator responses. While there isn’t any hard data on exactly how many species have actually gone extinct due to island tameness throughout history, experts believe numerous species have fallen victim to this phenomenon.

Island Tameness Definition

Charles Darwin first speculated about the theory that later became known as island tameness when he visited the Galápagos Islands in the mid-1800s. He noted that animals on the islands were less wary of predators compared to their relatives on the mainland.

Darwin reasoned that this tame behavior evolved on remote oceanic islands where natural predators were rare or absent to eliminate unnecessary escape responses, which cost the animals time and energy that could be used in other biologically beneficial activities, like mating or foraging for food. This island tameness, also known as animal naiveté, is a consequence of evolution and natural selection.

Since his conjecture, numerous studies have proven that Darwin was right. Studies focused on island tameness aim to measure it by understanding flight initiation distance (FID), the distance at which an animal will flee from an approaching threat, like a human or other predators.

A 2014 study on island tameness looking at FID in 66 different lizard species found that FID decreases as the distance from the mainland increases and is shorter in island populations as compared to mainland populations. Both of those conclusions support the theory of island tameness.

After the introduction of a lizard population to an island with low predation, FID decreased within 30 years, showing that the evolution of island tameness can move quickly. And, as shown by deer in the absence of predators, island tameness can linger for thousands of years.

The Problem With Animal Naiveté

Island tameness is evolutionarily disadvantageous for animals who live in areas where humans introduce predators. For tame animals, the concept of predators is brand new and they likely have no instinct to avoid them or consider them threats.

This animal naiveté can be reduced or eliminated in some species over time, but not all are so lucky. Many isolated island populations are too small or reproduce too slowly to adapt to predators. Some, like the dodo, go extinct as a result.

In a study testing the stress levels of marine iguanas on the Galápagos Islands, the reptiles did show the ability to learn appropriate predator responses from experience, despite their prior development of island tameness. However, researchers say the iguanas still likely wouldn’t survive in the face of introduced predators because the magnitude of change in this one-time experience was small and not sufficient to allow the species to thrive in the long term. The longer a species is without predators, the more difficult it is to develop predator responses quickly enough to avoid extinction, and this particular species was separated from predators between 5 million and 15 million years.

In general, the prevention of predator introduction remains a crucial conservation effort to support native and island tame species. Scientists agree that more studies are needed on the introduction of predators and its effect on island tameness, and whether or not island tameness can be resolved without causing steep population declines or extinctions.

Examples of Island Tameness

Dodo

Dodo Illustration
19th Century Dodo Illustration. Andrew_Howe / Getty Images

The dodo is an iconic now-extinct bird species endemic to the island of Mauritius, off the coast of Madagascar. Experts believe that the large, flightless pigeons went extinct in 1690, less than 200 years after they were discovered by the Portuguese. In that time, they were overhunted and mistreated by humans.

Because they were conditioned to living in a predator-free paradise, dodos were not wary of humans and were, therefore, easier to hunt. Humans also brought animals like pigs and monkeys with them to the island, which ate dodo eggs and competed with the birds for food. Those problems, combined with human-caused habitat loss, led to the demise of the bird. The dodo has since become a symbol of extinction and a prime example of the importance of conservation.

Yellow-Eyed Penguin

Yellow-eyed penguin.
Yellow-eyed penguin (Megadyptes antipodes), Curio Bay, New Zealand. thomaslusth / Getty Images

One of the flagship species for New Zealand’s wildlife tourism is the endangered yellow-eyed penguin. The species is generally unafraid of humans because they have evolved in the absence of predators, facilitating the development of animal naiveté. But experts have rising concerns that human tourism is having a negative effect on the flightless bird’s population.

The consequences of their island tameness and the introduction of predators (humans and invasive species like dogs and cats) include reduced juvenile survival and overall population declines, according to a study on yellow-eyed penguin exposure to unregulated tourism. Conservationists urge visitors to avoid penguin breeding areas and landing beaches to prevent further damage to the population.

Aegean Wall Lizard

Wall lizard in its natural environment
Wall lizard (Podarcis muralis) in the island of Samothrace, Greece. Cristi Savin / Getty Images

Endemic to the southern Balkans and many Aegean islands, the Aegean wall lizard is a small, ground-dwelling lizard that likes to camouflage into its surroundings. 

A study of Aegean wall lizard populations on 37 different oceanic islands found that these small reptiles exhibit island tameness that depends on the amount of time their habitat has been isolated from the mainland. Researchers found that lizards who lived on islands that had been isolated from the mainland the longest waited longer to flee from predators than those on younger islands.

Aegean wall lizards have further supported the theory of animal naiveté on predator-free islands and have demonstrated that extreme island tameness can result from many years of isolation from predators. Conservationists can use that knowledge to prioritize their efforts.

View Article Sources
  1. Cooper, William E., et al. "Island Tameness: Living on Islands Reduces Flight Initiation Distance." Proceedings of the Royal Society B, vol. 281, no. 1777, 2014., doi:10.1098/rspb.2013.3019

  2. Vitousek, Maren N., et al. "Island Tameness: An Altered Cardiovascular Stress Response in Galapagos Marine Iguanas." Physiology and Behavior, vol. 99, no. 4, 2010, pp. 544-548., doi:10.1016/j.physbeh.2010.01.016

  3. Blumstein, Daniel T. "Flight-Initiation Distance in Birds Is Dependent on Intruder Starting Distance." Journal of Wildlife Management, vol. 64, no. 4, 2003, pp. 852-857., doi:10.2307/3802692

  4. Stankowich, Theodore and Coss, Richard G. "The Re-Emergence of Felid Camouflage with the Decay of Predator Recognition in Deer Under Relaxed Selection." Proceedings of the Royal Society B, vol. 274, no. 1607, 2007, pp. 175-182., doi:10.1098/rspb.2006.3716

  5. Sih, Andrew, et al. "Predator-Prey Naïveté, Antipredator Behavior, and the Ecology of Predator Invasions." Oikos, vol. 119, no. 4, 2010, pp. 610-621., doi:10.1111/j.1600-0706.2009.18039.x

  6. Rodl, Thomas, et al. "Tameness and Stress Physiology in a Predator-Naive Island Species Confronted with Novel Predation Threat." Proceedings of the Royal Society B, vol. 274, no. 1609, 2007, pp. 577-582., doi:10.1098/rspb.2006.3755

  7. Silva-Rocha, Iolanda, et al. "Snakes on Balearic Islands: An Invasion Tale with Implications for Native Biodiversity Conservation." PLOS ONE, vol. 10, no. 4, 2015, pp. e0121026., doi:10.1371/journal.pone.0121026

  8. Bergman, Jerry. "The History of the Dodo Bird and the Cause of Its Extinction." Perspectives on Science and Christian Faith, vol. 57, no. 3, 2005, pp. 221-229.

  9. Ellenberg, Ursula, et al. "Elevated Hormonal Stress Response and Reduced Reproductive Output in Yellow-Eyed Penguins Exposed to Unregulated Tourism." General and Comparative Endocrinology, vol. 152, no. 1, 2007, pp. 57-63., doi:10.1016/j.ygcen.2007.02.022

  10. Brock, Kinsey M., et al. "Evolution of Antipredator Behavior in an Island Lizard Species, Podarcis erhardii (Reptilia: Lacertidae): The Sum of All Fears?" Evolution, vol. 69, no. 1, 2016, pp. 216-231., doi:10.1111/evo.12555