The Disappearing Birds of Hawai’i

My family spent six days in Kaua‘i, the Garden Island, the lushest, calmest, and (perhaps) prettiest of all the Hawaiian islands, with stunning natural features and abundant hiking trails. For me, an added bonus was the possibilty of seeing some rare and unique birds. Even though it is one of the smaller islands, Kaua‘i is second only to the Big Island in avian endemics, or species that occur naturally only in that place. There are six bird species found only on Kaua‘i. I was excited about the chance to see these birds in their native habitat.

As often happens, reality did not match my expectations. On Kaua‘i, the most ubiquitous bird—present in every parking lot, beach, and forest on the island—is the chicken. According to local lore, the Kaua‘i chickens are descended from birds that escaped into island jungles when their coops were destroyed during Hurricane Iwa in 1982 and Hurricane Iniki in 1992. Feral chickens are found on other Hawaiian Islands, but not in the large numbers that they are found on Kaua‘i. These chickens have become the unofficial mascot of the island. To be fair, they are not the drab egg-laying machines you would expect to find on a mainland farm. They are quite colorful and active, and my son, at least, was delighted by their omnipresence. We came home with a souvenir refrigerator magnet for our collection, adorned with a regal-looking rooster. I went to Hawai‘i to observe the richness of native birdlife, and I came home with a chicken magnet.

Until recently, the Hawaiian Islands truly were a wonderland of exotic and colorful birds, most of which have now been lost forever. Before the arrival of humans, 142 distinct bird species found nowhere else on the planet inhabited every ecological niche in the islands. Over millions of years, they adapted to changing environments. They diverged, evolved into separate species, and developed new feeding habits, beak shapes, and behaviors; and they took full advantage of the scarcity of native predators. We know of these species only because their bones and fossilized remains have been found in lava tubes, paleontological deposits, and archaeological sites. From flightless ibises to bird-hunting owls and a spectacular variety of honeycreeper, the diversity was astonishing. Today, ninety-five of those magnificent bird species are extinct; of those that remain, thirty-three of forty-seven (roughly 70 percent) are listed as endangered species. One-third of the endangered bird species in the United States are Hawaiian. The prospects for many of the surviving native Hawaiian birds are not encouraging. Introduced diseases, habitat loss, and the introduction of nonnative predators such as rats, snakes, cats, and mongooses threaten their survival in the wild.

The real trouble for Hawai‘i’s birds started with humans. The first wave of extinction began with the arrival of Polynesian maritime voyagers some 1,600 years ago. Flightless megaducks, geese, and rails were easy prey for Polynesian hunters, and their eggs and young were targets for the rats, dogs, and pigs Polynesians brought with them. High-ranking Polynesian chiefs (ali‘i) decked themselves in lavish cloaks (‘ahu ‘ula) and helmets (mahiole) constructed from the colorful feathers of local birds, which were believed to provide physical and spiritual protection for their wearers. Each cloak and helmet required hundreds of thousands of feathers to manufacture. Although birds were not killed for this endeavor, but rather captured in order to pluck their feathers and then released back into the wild, the practice may have stressed local avian populations. The clearance of native forests by Polynesian farmers also stressed bird communities and likely contributed to extinctions.

Captain James Cook’s arrival at Waimea Bay on Kaua‘i in 1778 jump-started a second, continuing wave of avian extinctions. The establishment of European and American farming and ranching enterprises and urban development resulted in widespread habitat destruction and brought a new selection of introduced predators. These included the black rat (Rattus rattus), which, unlike the Polynesian rat (R. exulans), can easily climb trees and raid bird nests. Perhaps the most devastating introduction was the mosquito, which led to deadly outbreaks of avian pox beginning in the mid- to late 1800s and avian malaria starting sometime in the early twentieth century. Today, only twenty-one native songbird species remain on the Hawaiian Islands; eleven of these are listed as endangered, and most are restricted to high mountain regions where mosquitoes cannot survive. And as the world warms from anthropogenic climate change, mosquitoes are moving into these high-altitude refugia, spelling potential doom for Hawai‘i’s endangered birds.

The challenges facing Hawai‘i’s avifauna are a part of a biodiversity crisis on a scale the Earth has not seen for over sixty-five million years. We do not know for certain how many unique plant and animal species are lost every day, because many species are unidentified and others, including entire regions and groups of plants and animals, are understudied. But computer models suggest that somewhere around 150 species are driven to extinction every single day.

From the perspective of geologists and climate scientists, the history of Earth’s flora and fauna over the past 450 million years can be seen as a play with five acts. These consist of five mass-extinction events—episodes of sudden, dramatic change in the Earth’s climate and environment, when at least half the planet’s macroscopic plants and animals vanished. Geologists have used these events to demarcate geologic epochs or time markers in the Earth’s history. Most of them took place so long ago and under such mysterious conditions that they are, for the most part, poorly understood by scientists.

The largest and most devastating mass extinction in Earth’s history was the Permian-Triassic event 252 million years ago, which resulted in the extinction of over 95 percent of Earth’s species, including 70 percent of land-dwelling vertebrates. So much life was wiped off the face of the planet that it has been colloquially dubbed the Great Dying. This event almost resulted in the end of life on our planet. Understanding how and why it occurred is difficult. The Permian-Triassic extinctions occurred in pulses. The earliest was the result of gradual environmental change, and the later pulses were likely triggered by an asteroid or comet impact, the Siberian Traps (massive volcanic eruptions that lasted roughly two million years), sea floor methane release, or some combination of these phenomena.

The most recent mass extinction event is the one with which you are probably most familiar—the Cretaceous-Paleogene or K-T boundary event. (The name K-T is derived from the German word Kreide, meaning “chalk,” referring to the chalky sediment of the Cretaceous Period, and the word tertiary, traditionally used to describe the interval spanning the Paleogene and Neogene periods.) Most geologists attribute it to a massive meteorite or comet impact 65.5 million years ago near Chicxulub, Mexico, although others implicate changes in atmospheric carbon dioxide or tectonic plate movements. The K-T event resulted in the extinction of about 76 percent of terrestrial species within just a few millennia, including nonavian dinosaurs, early mammals, and amphibians, birds, reptiles, and insects. Also wiped out were marine reptiles like mosasaurs and plesiosaurs and one of the most diverse families of animals on the planet, ammonites.

Of course, extinction is part of life on Earth. For billions of years, new species of plants and animals have evolved on our planet, outcompeting and replacing other species, resulting in the rich biodiversity, past and present, that we know today. About 98 percent of all the plant and animal species that ever existed on our planet are now extinct. Generally, when a species goes extinct, a new one fills the empty ecological niche, and life marches on. When everything is operating normally, Earth’s extinction rate is comparatively slow: between 0.1 to 1 species per 10,000 species over one hundred years. Known as the background extinction rate, this is part of our planet’s functioning. Life on Earth steadily changes as living things adapt to gradually changing conditions.

Mass extinctions, by contrast, are disruptive and critical turning points in biotic evolution. They wipe out fit and unfit species alike and result in dramatic declines in biodiversity. Recovery from such events takes millions of years and results in the transformation of floral and faunal communities. It took more than ten million years for mammals to evolve into the diverse array of species that rivaled the diversity of the dinosaurs after the K-T boundary extinction event. During mass extinctions, new species cannot evolve fast enough to fill the ecological role performed by the extinct species. Their absence can result in cascading effects throughout ecological and planetary systems.

A growing consensus among the scientific community is that we are living in the midst of another mass extinction. Since it is occurring around us, it is impossible to predict the results or know how it will compare to the previous “Big Five.” But according to current calculations, the rate of modern extinctions is one hundred to one thousand times higher than background levels. At this rate, the sixth extinction could result in a 50 percent loss of the remaining plant and animal life on Earth. This loss in biodiversity would be catastrophic. It could trigger the collapse of entire ecosystems. For humans it could spell the loss of critical food economies, the disappearance of medicinal and other resources, and the demise of important cultural landscapes and seascapes. Many species are teetering on the brink: extinctions threaten one-third of amphibian species, nearly one-third of corals, one-quarter of all mammals, and one-eighth of all birds.

Extinctions of plants and animals can have far-reaching implications for the health and functioning of our world. Coral reefs, for example, protect coastlines from the damaging effects of wave action and storms. They are also the source of nitrogen and other essential nutrients for marine food webs and of food and new medicines for human communities. Their loss would be devastating to life on the planet.

The undeniable cause of our current mass extinction crisis is us. Humans have already transformed more than 70 percent of Earth’s land surface and have put to use about 75 percent of the world’s freshwater. Industrialized agriculture often results in soil degradation, deforestation, pollution, runoff, and biodiversity declines. Plowing disrupts soil ecologies. Planting vast fields with a single crop (monocropping) drives out species from their natural habitats and creates conflicts between humans and wildlife.

Some species are known as keystone species because of their critical importance to specific ecosystems. These include wolves, which help keep the population of grazing animals in check, and beavers, whose dams help regulate water flow in river ecosystems. When humans target these species, as pests or as resources, their removal can cause cascading effects across entire habitats.

If removing species can be destructive, so can introducing new species in the wrong place. Humans have been responsible for transporting invasive species across the globe—sometimes deliberately, sometimes accidentally. Introduced species compete with native flora and fauna for resources and often reduce local biodiversity. When native species are ill-equipped to compete with the new arrivals, the result may be extinctions of rare native plants and animals. Finally, human contributions to greenhouse warming and climate change have triggered environmental changes at a scale and rate to which many species are unable to adapt. The International Union for the Conservation of Nature (IUCN) estimates that because of anthropogenic climate change, nearly eleven thousand species on their Red List of Threatened Species face increased likelihood of extinction.

Bad as this news is, I see a silver lining. The mass extinctions of the deep geological past occurred long before our earliest human ancestors appeared about seven million years ago. The Big Five mass extinctions were all caused by extreme temperature changes, dramatic fluctuations in sea levels, or catastrophic one-off events like colossal volcanic eruptions or extraterrestrial objects hitting the Earth. There is little we could do to prevent or mitigate the effects of an event of this kind. But since the current mass extinction is a crisis humans have created, that also means we can fix it. We can find ways to live more sustainably and reduce the loss of biodiversity around the world. We can study the causes and effects of human-induced plant and animal extinction and work to curb them. We can identify our most harmful activities and find alternatives or ways to reduce the negative effects. Doing so is important not just for the plants and animals being driven to the brink of extinction (and beyond): it is important for the quantity and quality for our time on Earth.

Since the sixth extinction is often strongly linked to recent or modern human activities beginning with the Industrial Revolution, the study of deep history may seem to offer little information relevant to the current crisis. However, humans have driven extinctions, at a slower rate, for millennia. Many of these have shaped the character and composition of modern land- and seascapes. Understanding the roots of the sixth extinction, using archaeological and paleoecological evidence, is critical for stemming the tide of plant and animal extinctions and preserving biodiversity. Lessons from history allow us to find ways to help and to evaluate whether our efforts are effective.

Understanding Imperiled Earth is a new release from Smithsonian Books. Visit Smithsonian Books’ website to learn more about its publications and a full list of titles. 

Excerpt from Understanding Imperiled Earth © 2024 by Todd J. Braje