The passenger pigeon used to be the most numerous bird on Earth. Then, in less than a century, it was driven to extinction at the hands of humans. This month marks the 100th anniversary of Martha, the last passenger pigeon’s death.

There used to be billions of passenger pigeons. Literally. And that’s passenger pigeons, not carrier pigeons by the way, which are still alive and well today. When Europeans arrived in North America, there were between 3 and 5 billion passenger pigeons there. The passenger pigeon, Ectopistes migratorius, were highly sociable, living in huge colonies with up to 100 nests in a single tree.They migrated annually from Quebec to Texas and Florida and their flocks could turn the sky black as they flew over. It seemed there was a never-ending supply of passenger pigeons. But humans proved that there was indeed an end, as they hunted them to near extinction.

Soon after Europeans arrived in North America, they began clearing the huge forests that provided food for this vast pigeon population, and by 1872 half of the continent’s forest had been cut down. In the 19th century, to add insult to injury, people in North America began hunting the passenger pigeon. Because they were so numerous, and relatively unfazed by being shot at, they were incredibly easy to kill and their meat was sold cheap. This is an evolved response – living in large groups, loss of individuals due to predators would hardly make a dent, and the risk to any individual pigeon is minimal, so it makes little evolutionary sense trying to escape or avoid predation. Unfortunately for the passenger pigeon, humans could make a dent. They use nets, guns, fire and toxic fumes to maximise their killing power, some hunters bringing in millions of birds a year. And recent research indicates that passenger pigeon populations naturally showed extreme fluctuations due to natural variations in food availability and climate. The species may have already been in decline when humans started cutting down their habitat. No doubt humans played a key role in their demise, however. Another problem for the passenger pigeon was a relatively slow reproductive system; each female laid a single egg each year, making it hard to replace the huge numbers of birds that were being killed and eaten by people.

As their numbers dwindled, some conservations tried to stop their extinction, and a few laws were passed to restrict hunting in nesting areas. However, it was too little, too late and the rules were poorly enforced. Passenger pigeons probably had some critical point at which flocks were too small and vulnerable to predators, and humans pushed them passed this tipping point. After that, there was nothing that could be done. Captive birds soon became the subject of breeding programs, and in 1902 a single female bird, named Martha, was sent to Cincinnati Zoo to initiate a breeding program there. Sadly, as numbers declined alarmingly fast, the zoo was never able to find her a mate, and Martha remained in the zoo for the rest of her life.

Martha, named after George Washington’s wife, was the last passenger pigeon ever to live on Earth. She died of old age, but the rest of her species were lost to massive overhunting, deforestation and disease. By 1900 there were none left in the wild, and Martha’s death in 1914 marked the extinction of a species. After her death, Martha was mounted and has since been displayed in various collections across the USA.

What make’s Martha’s story so important is that it highlights our horrendous ability to eradicate species, even those that seem so numerous and to be essentially infinite. It is all too easy, as it turns out, to drive a species to extinction. Species such as the turtle dove in the UK may face a similar fate if pressures such as habitat loss and disease are not ameliorated. The turtle dove’s numbers are halving ever 6 years, making them the UK’s fastest declining bird species, losing 95% of their population since 1970. Martha is a cautionary tale, that we should never take a species for granted, and that we must start conserving species now, before we pass the point of no return.