For the Birds: Human-caused Bird Extinctions

Tuesday is Earth Day. I hope you will take the time to think about how you can make a difference in the protection and conservation of our planet’s organisms and resources. Go to http://ww2.earthday.net/ to find out about Earth Day activities in your local area.

In the last column, I wrote about sources of bird mortality. Many birds die because of direct human activities (for example, overhunting) or indirect effects of our use of the earth (for example, habitat destruction and pollution). Today, we will consider birds that have been pushed over the brink to extinction because of human activities. This sobering topic should make us all take Earth Day even more seriously. Extinction is forever.

Over the past 500 years, over 140 species of birds become extinct. With the exception of only about a dozen species, these birds were driven to extinction by human activities. Of the roughly 11,000 existing birds species, 1200 are currently in danger of extinction.

The majority of these extinctions occurred on oceanic islands. Many of these islands are small so population sizes are never very high. Many birds on oceanic islands become flightless over time and are therefore not able to escape from human hunters. Finally, birds on oceanic islands with few predators are often fearless in the presence of humans or introduced predators.

The Dodo provides an instructive case study for the extinction of island bird species. This species belongs to the order of birds that includes the pigeons and doves. The Dodo was flightless and most individuals were about three feet tall, weighing more than 40 pounds. They were found only on the island of Mauritius, an island off the coast of Madagascar. Dodos were fruit eaters in the Mauritian forests.

Dodos were certainly extinct by 1681, only 174 years after Europeans first became aware of them. Their demise began with the colonization of Mauritius by Dutch settlers around 1600. Although Dodos would have been easy for humans to kill, journals of Mauritian visitors indicate that the meat of Dodos had an unpleasant flavor and was quite tough. Humans hunted other birds, like the Red Rail, for food. The dramatic decline of the Dodos was rather caused by the cats, pigs and monkeys (Crab-eating Macaques) that the Dutch settlers brought with them. These introduced animals took the eggs or nestlings from the Dodo nests on the ground. By cutting forests and hence reducing Dodo habitat, humans accelerated the extinction of the Dodo.

Mauritius and nearby islands were home for 27 species of birds found uniquely on those islands. Today, 24 of those species are extinct. Such is the footprint of human settlement.

Hawaii is notable for a remarkable suite of birds called Hawaiian honeycreepers, found only in Hawaii. Related to our finches, the honeycreepers have not fared well with human development of the Hawaiian Islands. In the past 200 years, ten of the 31 species have been driven to extinction and several others are endangered.

Understanding the causes of extinctions is sometimes difficult. In New Zealand, 25 species of flightless birds called moas existed until about 300 years ago. We know that Maoris colonized New Zealand about 650 years ago and certainly ate moas and their eggs. However, the New Zealand climate has been changing over the past thousand years, reducing the grasslands the moas favored at the expense of expanding forests. How much of the blame for the extinction of the moas should be pinned on humans? We don’t know for sure.

But bird extinctions don’t happen only on islands. We have lost at least three species of North American birds in the past 200 years. We can clearly point an accusing finger at ourselves for two of these extinctions.

The Passenger Pigeon was once the most abundant bird in North America, migrating in astoundingly large flocks. They were colonial breeders, nesting sometimes in groups of 100,000 birds or more. The pigeons were hunted commercially as a cheap food for slaves and the poor. The pigeon population declined slowly from 1800 until 1870. As a result of more sophisticated capture techniques, the Passenger Pigeon population plummeted over the next 20 years with the last major harvest taken in 1896. These pigeons, once numbering in the billions, were hunted to extinction.

The Carolina Parakeet, the only parrot in eastern North America, went extinct because of deforestation and the killing of birds for use in ladies’ hats and for protection of fruit crops.

We know little about the extinction of the Labrador Duck. In all likelihood, the Eskimo Curlew and Bachman’s Warbler are extinct as well with humans having a significant role in their decline.

[originally published on April 21, 2008]