The Plight of the Passenger Pigeon

The Passenger Pigeon (Ectopistes migratorius) was once the most adbundant bird in North America, possibly in the world. Humans hunted them on a massive scale in the 1800s, and they were driven to extinction in the early 1900s. Have we learnt anything from the plight of the passenger pigeon?

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Painting of a male passenger pigeon (Wikipedia)

A course about conservation

I’ve been taking the Massive Open Online Course (MOOC) “Introducing Conservation” offered by United for Wildlife. United for Wildlife is a collaboration between seven big conservation organisations, and has the Duke of Cambridge as President. Their course aims to educate people all over the world about conservation, and encourages people to get involved themselves. I’m always keen to expand or refresh my knowledge, especially when there are certificates to reward the worthy! I’m currently working through Lesson 1: Life on Earth, and one of the exercises asked me to write briefly about an extinction from the last 500 years. I chose to write about the Passenger Pigeon, a dramatic example of human-caused extinction due to both the huge numbers involved and the short timescale over which it occurred.

The world on the wing

What was incredible about the passenger pigeon is the size of the original populations; with an estimated 3-5 billion birds in existence when Europeans discovered America, this was the most abundant bird at the time. The birds would move around in huge flocks that could darken the sky!

It is believed that flocking and nesting together in large numbers allowed the populations of passenger pigeon to make use of bumper food sources and to survive predation through satiation – a normal predator would be unable to make much of a dent on these large roving flocks.

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Shooting pigeons in Louisiana (Wikipedia)

The decline

Although there were large numbers of these birds, large-scale exploitation by humans for meat in the 1800s drove down numbers (although habitat destruction would have played a part too). Gathering together in large numbers made the passenger pigeon particularly vulnerable to professional hunters with modern techniques.

By 1860 the bird numbers showed signs of decreasing, and by the 1890’s the passenger pigeon was almost gone from the wild. Some efforts were made to protect the species, but it was too late. The passenger pigeon was adapted for life in large flocks: both the few individuals left in the wild and the small flocks in captivity were unable to successfully reproduce and restore the species. The last individual died in captivity in 1914.

Conclusions

So what can we learn from this extinction?

At the time people would have been unable to believe that such an abundant bird could be pushed to extinction. And yet it happened, and it happened very quickly. Although passenger pigeons lived in huge numbers, they depended on those numbers to survive. There was a critical point, a threshold, beyond which the population collapsed.

Although the passenger pigon is a particularly dramatic example, this can be applied to other species too. Once populations are pushed beyond a certain limit, they may struggle or be unable to recover naturally as other processes start to take hold. Extinction can therefore happen much more easily than we would expect. This has since been termed an Extinction Vortex, and it pushes declining populations into greater decline. The point at which it comes into effect will vary between species, depending on how they are adapted. It is therefore pretty important to maintain population sizes when trying to conserve wildlife!

Do you have any other examples of recent extinctions? Please post in the comments!

What caused your example species to decline initially? Did any other factors come into play to hasten the extinction?

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