Passenger Pigeon

Like the dodo bird, the passenger pigeon is often near the top of the list when the subject of extinction is discussed. Known as a beautiful bird that formed the largest colonies known to man, this large blue, gray and pink bird were found across the eastern United States and north into Canada.

Early settlers recounted stories of downing two dozen birds with a single shotgun blast. Their flocks were so large the sounds of their beating wings could be heard miles away. Others describe passenger pigeons breeding in colonies so enormous that large trees would fall over under the weight of the birds. It’s easy to understand how they were such an important source of food for people living in the frontier.

Yet despite being the most common bird on the planet in the 1840s, passenger pigeons completely disappeared within seven decades. It’s easy to understand the extinction of a flightless bird living in isolation on a tiny island in the Indian Ocean, but how could the most common bird to have ever lived disappeared over such a wide range?

In this blog, we’ll discuss how a bird numbering in the billons become extinct so quickly.  How was it that their unique life cycle that protected them for generations led to their eventual extinction? What value did they gain by only laying a single egg? How could tens of millions of birds breeding in an area totaling just a few square miles find enough food to feed themselves and their squabs? Finally, we’ll review whether survivors can still be found today and whether cloning can used to bring them back.

Unlike most passerine birds, the passenger pigeons used the saturation method of breeding to raise their squabs. This method of breeding involves a species giving birth to a massive number of young at the same time over a confined area to enhance their offspring’s ability to avoid predators. Basically, so many baby pigeons are born in a confined area that predators are overwhelmed with the available food supply, allowing the majority of the birds to reach adulthood.

A young passenger pigeon

The general belief is that the passenger pigeon’s saturation breeding method which protected them for generations, ultimately led to their extinction. This breeding method brought together tens of millions of birds over an area covering several square miles. Hunters would  gather at these localities to kill truckloads of birds to be shipped to market. They could simply pull up to one location and shoot thousands of birds in one day. Considering the large market for wild pigeon meat, hunters could earn a year’s salary in as little as one or two weeks.

Passenger pigeons that made it through these hunts, were further damaged as the terrible disturbance would have prevented them from breeding. Over just a handful of seasons, the entire flock would be devastated.  

The last great passenger pigeon hunt was said to only contain around 100,000 birds. It was said that after the hunt, the bird was never to be seen in significant numbers again. The remaining birds that lived in captivity were mostly sold to individual collectors with very little effort made to save them through captive breeding. 

Unlike almost every other passerine bird alive today, the passenger pigeon only laid a single egg. The parents did not care for the birds until they were fully fledged and instead kicked them out of the nest after 14 days, weeks before they were able to fly. The squabs were left on their own to search for food on the forest floor.

I have always been interested in this breeding habit as it seems to have been unique among bird species. What value was to be gained by this breeding method? How could their population continue when a female passenger pigeon’s only squab that season was left to fend for itself?

To maintain their species, birds and other wildlife will over produce offspring with the hope that at least two will make it to adulthood to allow for the continuation of the species. Most bird species will produce in the neighborhood of 20 young during their lifetime. A common house sparrow can raise an average of 4 babies every year of 5 breeding season to produce 20 young. Even a bald eagle will raise 10 to 15 babies during their life. Why then did the passenger pigeon only lay one egg at a time? They only lived for around 8 years, so this ration of offspring to long term survivors stands out from other birds.

Did they have a special adaption for survival or was there another reason that they only laid a single egg? After years of reading about the passenger pigeon, I read an article in which a scientist speculated that the birds would raise multiple clutches during their breeding season.

This belief would help explain several aspects of the bird that have been difficult to grasp. Almost all flighted birds are cared for by their parents until they are able to fly on their own protecting them from predators lurking on the ground under the nests.

On the other hand, researchers have found that baby passenger pigeons were kicked out of their nest well before they were able to fly. They were left on their own to find what food they could while waiting for their flight feathers. This a really unusual type of breeding as they would have been an easy meal for the many coyotes, foxes, raccoons and other predators found in their breeding grounds.

What value were the birds to gain by abandoning their only offspring so quickly? If the parents took turns caring for the young, they would be able have time to forage for their own food, avoiding the starvation period that some species of birds experience.

I think that the obvious answer to abandoning their young so quickly allowed them to immediately raise a second and possibly third nestling during the brief breeding season. This type of breeding would increase their total number of offspring from around 7 (if only one bird is raised per season) to 20 plus progeny which would be in-line with most other passerine species.

Food sources

Every article that I’ve read on the passenger pigeon describes their flight north to their breeding grounds where they would gorge on nuts and acorns, followed by their fall migration back to their southern wintering grounds.

Sounds simple enough, but even their food sources leaves unanswered questions. Nuts and acorns are produced in the fall, supplying bears, deer, squirrels and other animals a bountiful harvest to help them survive through a cold Michigan winter. However, billions of pounds of these masts would have to been left over to feed the enormous flocks of passenger pigeons.  Could they have been the primary breeding food source for the pigeons?

It seems more likely that their primary food source in the spring would have been worms and insects awakening after the long winter. However, it wouldn’t take long before the forest floor was picked clean within 5 miles of their nesting grounds.

Instead, I’m of the opinion that during the breeding season, the male and female passenger pigeon would have shared in the care of their young. This would allow each parent to fly many miles away from their nesting grounds to find food sources not yet picked cleaned by the incredibly large flocks. This would have taken an enormous amount of energy to feed both themselves and their young, which may help explain that only one squab was raised at a time.

Outside of the breeding season, passenger pigeons would once again form small flocks to reduce competition from available food sources. At some point late in winter, the birds would then begin to form larger and larger flocks, until tens of millions of birds were ready to fly north once again. However, I have been unable to identify a study that figured out how the birds knew where to gather before flying north. I’m not aware of another species that spent half the year in small populations that then gathered into enormous gatherings to migrate to their breeding grounds.

Are there any living passenger pigeons?

Considering that for generations, passenger pigeons used the saturation breeding method, it would be highly unlikely that today, a handful of baby passenger pigeons kicked out of the nest before they could fly would be able to avoid predators long enough to make it to adulthood.

I’ve come across several websites where birders have stated that they found a living passenger pigeon, but the articles usually ended with a blurry photograph or a statement that they did not have a camera with them. I don’t doubt the sincerity of them, but passenger pigeons can easily be confused with an unusually colored mourning dove.

What about cloning?

Anyone interested in learning about efforts to de-extinct the passenger pigeon should visit the Revive and Restore website (http://reviverestore.org). This team consists of some of the greatest scientific minds in the world working together to figure out how to clone extinct species seemingly lost to us forever.

Using band-tailed pigeons (their closest living relative), the researchers expect to insert passenger pigeon genome into the genome of a band-tailed pigeon to produce a bird that looks and behaves like a passenger pigeon. The team hopes to hatch the first passenger pigeon in 2025 for eventual release into the wild by 2040.

Whether this is wishful thinking or actually is possible is difficult to say. I visit their blog quite frequently looking for the latest effort made to bring about the de-extinction of this magnificent bird.

Photographs and video of living passenger pigeons

Unlike the Carolina parakeet in which I’ve been able to only find two photographs of a living specimen, there are dozens of photos of passenger pigeons living in aviaries in the late 1800s to early 1900s. We been fortunate to find photos taken of breeding birds and their offspring. A google search for “living passenger pigeon” will identify multiple photos. Due to the fact that the last known passenger pigeon died in 1914 (Martha at the Cincinnati Zoo)