The Return of the Black-footed Ferret

The rise, fall, and rise of one of North America’s rarest mammals

A The black-footed ferret (Mustela nigripes) is a small carnivorous mammal, similar in length to a domestic cat, and is the only ferret species native to North America. For at least 100,000 years they lived in an area that extended almost uninterrupted from southern Canada to northern Mexico. But numbers fell dramatically throughout the 19th and 20th centuries, to such an extent that the black-footed ferret was declared "possibly extinct". Then, almost miraculously, it returned from the dead.

B Within the genus Mustela, the ferret belongs to the subgenus Putorius, of which there are only three extant species: the European polecat, the Siberian polecat and the black-footed ferret. The European polecat lives in open forests and meadows and is thought to be the ancestor of the domestic ferret. The Siberian polecat looks more similar to the black-footed ferret and leads a similar life on open grasslands and semidesert regions across Russia, China and Siberia.

C Ferrets probably evolved in Europe between three and four million years ago and dispersed into North America across an ice-age land bridge at least two million years ago. They then advanced south-eastward to the Great Plains through ice-free passageways. The black-footed ferret’s history in North America is inextricably linked to the creature which became almost its sole prey -- the prairie dog. These small rodents are a type of ground squirrel which live in networks of underground tunnels, known as burrows. The black-footed ferret’s short legs and long, slim body make it superbly adapted for life in the burrow systems of its prey.

D Spending virtually all their time underground, black-footed ferrets have always been elusive. Ferrets are never mentioned in accounts of the early explorers or pioneers who crossed the Great Plains by wagon train during the early to mid-1800s. They were, however, occasionally listed in records kept by fur companies in the upper Missouri River basin during that period. Black-footed ferrets were not officially recognised by scientists until 1851, when a description and drawing of one featured in a book by the renowned naturalist John James Audubon and Reverend John Bachman. For over two decades, no other specimens were seen, and scientists even began to question their existence. Then, in 1874, a Dr Elliott Coues issued a request for specimens through the popular magazine The American Sportsman, and was soon rewarded. With these he was able to add to Audubon’s description and confirm the existence of the black-footed ferret.

E In the decades that followed, European settlement across North America changed the landscape dramatically, with vast areas being transformed into crop and grazing land. As agriculture and ranching expanded, the black-footed ferret’s main prey, the prairie dog, became a target for extermination and was eventually eradicated from 98% of its original range. The result was devastating for black-footed ferret populations throughout the continent. Even today, the prairie dog is still trapped and poisoned because ranchers believe that it competes with livestock for grass -- a notion that belies recent research showing that prairie dogs and cattle feed on different plants.

F As late as the 1950s, black-footed ferrets were still thought to occur in low densities throughout most of their historic range. However, by the 1960s, the only known population was a small colony in south-western South Dakota. In 1967, the US Fish and Wildlife Service classified the black-footed ferret as an endangered species, and in 1974 the South Dakota colony disappeared. Finally, in January 1979, the last ferret in a captive-breeding programme died -- making the black-footed ferret the first mammal to be declared extinct in the Northern Hemisphere in the 20th century.

G But that was not the end of the story. In 1981, a farm dog called Shep carried an odd-looking creature to its owner’s ranch house in Meeteetse, Wyoming. The rancher put the carcass in his fridge and alerted state officials. The dog had found a black-footed ferret -- which led to efforts again being made to save the species. An intensive search in the region led to the discovery of a 130-strong population. This wild colony thrived for a while, but disaster struck again and the number of animals was drastically reduced by the disease distemper -- probably contracted from domestic dogs. In 1985, in a final bid to save the species, the remaining 18 individuals in the colony were trapped for a new captive-breeding programme. This project was successful, and there are now more than 2,000 black-footed ferrets in captivity across the US and Canada.

H A reintroduction programme began in 1991. Before they can be reintroduced into their natural habitat, captive ferrets have to learn to hunt and escape from predators. They are first held in pens on the prairie, where they are fed prairie dog meat. Once the ferrets associate these animals with food, keepers unleash live prey into the pens, and they soon realise that they must hunt or go hungry. Then, to get the ferrets used to living underground, they have to be tempted into the holes with food.

I Reintroduction programmes are now underway across central USA, but there is one location that is key. The Janos area on the US--Mexico border is the obvious place to reactivate the continent’s wild black-footed ferret population, being one of the most important remaining grassland ecosystems in the Americas and home to an abundance of prairie dogs. At the last report, the future of the black-footed ferret finally looks promising.

Marine Mammals Exhibit Their Ingenuity

Dolphins use "tools" to help hunt for food

In the deep, clear channels of Australia’s Shark Bay, bottlenose dolphins have discovered tools, raising questions about the origins of intelligent behaviour, the nature of learning and the birth of technology. There, dolphins in one extended family routinely use sponges to protect their noses as they forage for fish hidden in the abrasive seafloor sand, according to Georgetown University scientists.

As far as the researchers can tell, a single dolphin may have invented the technique relatively recently and taught it to her offspring. The simple innovation dramatically changed their behaviour, hunting habits and social life, the researchers found. Those that adopted it became loners who spent much more time hunting than others and dived more deeply in search of prey. The sponging dolphins teach the technique to all their young, but only the females seem to grasp the idea. "It is indisputably tool use," says primate anthropologist Craig Stanford at the University of Southern California, an authority on animal cognition and behaviour. For those seeking a glimpse of our own beginnings, the dolphins of Shark Bay offer a hint of the inventive impulse that occurred when our earliest ancestors first shaped destiny by fashioning implements with their hands.

Tool use of any sort among wild animals is rare, difficult to document reliably and controversial. The line between instinct, ingenuity and intelligence is easily blurred by wishful thinking, experts caution. Field observations often give rise to scholarly disputes. Even so, ten primate species of monkeys and apes, along with 30 species of birds, are thought to use sticks, rocks or leaves as tools.

In the first in-depth analysis of this natural dolphin behaviour, marine biologist and psychologist Dr Janet Mann at Georgetown University and her colleagues found that the dolphins of Shark Bay use their makeshift hunting masks more often than any other species uses tools, except human beings.

The curious hunting habit was first observed by a local fisherman who reported to marine biologists that he had seen a dolphin with an odd growth on its nose. Monitoring its movements through the bay’s unusually clear waters, researchers soon discovered that the dolphin was actually balancing a conical basket sponge on its nose.

At first, it was not evident what the dolphin was doing with a sponge. Observing from a small boat, Dr Mann and her colleagues eventually identified 41 dolphins who regularly used sponges to hunt, cataloguing 1,295 dives in which they surfaced with sponges on their snouts. Researchers were startled to realise that the dolphins of Shark Bay employed one living creature as a tool to help hunt another.

Not any basket sponge would do, the researchers soon learned. The dolphins might search for ten minutes to locate one with the right conical shape to cap their nose, tear it free of its mooring and then carry it to a preferred hunting ground along channels between eight metres and 13 metres deep. "You can see that they are scattering the sand gently as they go along," says Dr Mann. "When they startle a fish out of the sand, they immediately drop the sponge and go after it."

"They return to retrieve the sponge and pick up the hunt again, repeating the pattern. They really use these sponges as a foraging tool," says dolphin biologist Maddalena Bearzi, president of the Ocean Conservation Society of Los Angeles. "They discovered it could create an advantage in their foraging technique, and they pass it from generation to generation." However, among the hundreds of dolphins living in this bay, only a few dozen use sponges to keep from scraping their noses, and that offered researchers an opportunity to compare creatures that use tools with others of the same species that do not.

Although these dolphins all appear to be related, researchers at the University of New South Wales suggest that nurture, not nature, is the reason these dolphins use tools, ruling out genetic explanations for the behaviour. Instead, they are convinced that the use of sponges is passed from one generation to the next through imitation. Among bottlenose dolphins, mothers nurse their young for up to eight years, ample time for calves to absorb their mother’s hunting tricks by observation. "This is an example of culture among these animals," says Dr Bearzi. "This is part of the reason it is so important."

So far, almost all of the dolphin spongers have proved to be female. "The sex difference is really striking," Dr Mann says. "I don’t know of another species where it is so dramatic." Of the sponging offspring, only the daughters could be seen still sponging once they reached maturity. The sons tried it but almost always abandoned it. Male dolphins rarely play a role in child-rearing and tend to fish in packs.

For Dr Mann, the discovery that dolphins, too, are tool users adds an unexpected dimension to the history of innovation, shedding new light on animal intelligence. Clever mimics and fast learners, dolphins have unusually large brains -- four times the size of a chimpanzee’s and second only to humans in relative size. "It speaks to this whole issue of creativity and learning and brain size," she says. "The number one question that drives me and others is: Why do dolphins have such big brains? What are they doing down there in the water that requires them to be so smart?"

* Sponge: a very simple sea creature with a soft, porous body that lives attached to a surface.