What Is Extinction?
In biology, extinction is the complete loss of an entire species. It is the ultimate loss of biodiversity; once a species has gone extinct, it cannot return (though some scientists are attempting to “de-extinct” some species through cloning and similar approaches).
Extinction is a natural process, the ultimate end of the life cycle of a species. The dinosaurs are all extinct–although some evolved into the birds we see around us today–as are mastodons, saber-toothed cats, and the trilobites.
In fact, there have been five great extinction events in the history of life, where most of the plants and animals alive at the time disappeared, and only a few survived to repopulate the planet, albeit in very different forms. Although extinction is a natural process, the rate at which species are going extinct has accelerated dramatically in recent decades as humans have had greater and greater impact on our planet. Many scientists have concluded that today we are going through a sixth great extinction, this one driven primarily by us.
How do we know a species has gone extinct?
Though simple in concept, actually knowing that something is extinct – that is, that the last individual of a species has disappeared – is incredibly difficult. How do you prove the absence of something? The New Zealand Storm Petrel hadn’t been seen in over 160 years and was considered extinct, but in 2003 a group of birders spotted and photographed one; now over 1,200 photos of this species, including this one below, can be found in the collection of the Macaulay Library at Cornell’s Lab of Ornithology.
Scientists rely on extensive and intensive surveys in the wild to determine if a species still exists or has gone extinct. If sufficient effort is put in, but no solid evidence is found, then they conclude that the species is likely extinct. But how much effort is enough? Where do we draw the line? Cryptic species can often escape detection despite massive efforts, and there may be suitable habitat elsewhere that is not surveyed. And what constitutes solid evidence? Is a blurry photograph from a game camera enough? What if the animal is seen, but by a novice birder who didn’t take a photo? What about a footprint or a nest without any sighting of the animal? Or a recording of a distant call? Short of having a bird in the hand, there is always room for doubt.
Knowing whether a species is extinct is critical to making conservation decisions. If we know that some individuals of a species still exist, but in very low numbers, then that species often will become a priority for conservation efforts. On the other hand, if a species is thought to be extinct, then those resources can be directed elsewhere, to other endangered species that might be saved. The risk lies in concluding that a species is extinct when it is not, as diverting resources away from a critically endangered species may ensure its demise.
North Island Giant Moa
Known in Māori as kuranui, this large, herbivorous bird was one of the tallest birds ever to exist, stretching its long neck to reach a height up to twelve feet. Living on the North Island of New Zealand in lowland habitats like shrublands, grasslands and forests, the North Island Giant Moa laid large, fragile eggs which were incubated by the males, although the exact method is unknown. Along with much of the other native fauna, the North Island Giant Moa disappeared from New Zealand roughly 200 years after the Māori first arrived on the islands around the 13th century. It is believed to have been due largely to over-hunting, one of the common mechanisms behind extinction events driven by humans.