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)

Carolina Parakeet (Conuropsis Carolinaensis)

 

Many people do not realize that until relatively recently, the eastern United States had a native parrot that could be found as far north as New York and as far west as Colorado. The Carolina parakeet (Conuropsis Carolinaensis) was a small green parrot with a bright yellow head, reddish coloring around the eyes and an ivory bill. 

 

Early settlers wrote about large flocks of parrots living in old sycamore trees along meandering rivers of the Mississippi River Valley. Others describe parakeets playing in the winter snow in upstate New York. Considering that most parrots are tropical birds, scientist are still trying to uncover the many mysteries of the Carolina parakeet. Many important questions have been left unanswered following their extinction nearly 100 years ago.

To this day, the life cycle of the Carolina parakeet is poorly understood by scientists. Some writers stated that small flocks of the birds would share nest cavities in large sycamore trees in wetlands. Others described large, communal nests made out of sticks similar to those created by the monk parakeet. Still others mention parakeets breeding in the rafters of old barns.

 

Other unanswered questions include how these colorful birds survived winter temperatures below zero degrees. Some researchers believe that they migrated to warmer climates in the fall, while others point out winter sightings in Ohio. Their food sources are even under investigation due to their ability to eat seeds that are poisonous to all other birds. Even the most basic information on this bird remains unanswered.

What Happened?

I have always been interested in how this fascinating bird disappeared, despite having such a large habitat. Extinctions can usually be easily understood. Great auks were hunted for food until their numbers got so low that egg collectors paid large sums of money for samples, encouraging anyone with a boat to travel to remote islands to seek them out. The Dodo bird was driven to extinction by feral pigs, monkeys and rats introduced to their tiny, predator free island. These introduced species quickly targeted the slow moving bird at each stage of its life cycle.

Only a handful of birds have been lost from the U.S. outside of Hawaii. Most birds take precautions by nesting high in trees to avoid rats and raccoons or feeding in large flocks to keep watchful eyes on hawks and other predators. The Carolina parakeet shared both of these behaviors, so what happened?

Written records shared by early settlers moving westward often describe encountering great flocks of the birds numbering in the hundreds; these flocks soon disappeared altogether over a period of only ten to twenty years. This sudden collapse of the Carolina parakeet population greatly limited the ability of scientists to study these colorful birds.

Almost every firs- person account that I’ve read seems to follow the same timeline. Descriptions of huge flocks of Carolina parakeets when frontier towns were first settled, followed by the gradual reduction in numbers and finally their disappearance in under 20 years. Accounts mention specimens being shot and young teens climbing trees to steal baby birds, but these actions do not address the large-scale eradication of this species. Even stories of farmers killing birds in their orchards can’t address the complete collapse in their population, as most Carolina parakeets lived in isolated wetlands far from the nearest village. 

 

Over the last thirty years, scientists have concluded that something other than human interaction must have killed off the Carolina parakeets. Most are focusing on an unknown disease as the primary cause. This type of mass die-off due to disease is not unknown, considering the history of the American chestnut and the American elm.  

If they were truly killed off by disease, which disease was it? What could have killed off every parakeet over such a short period of time? Could farm animals brought with the early settlers be the host of the disease in question? It’s unlikely that cattle, pigs and other mammals were the host. Maybe the host animal was another bird.

Chickens are known to be hosts to several diseases that can kill other birds and even humans. It wouldn’t be out of the question that the smoking gun points at them at some time in the future.

Another potential killer is the honey bee. Some writers have speculated that bees took over the tree nests needed by the parakeet. My concern with this idea is that honey bees are often associated with human settlements, while the Carolina parakeets were believed to nest in sycamore trees in swamp land (or as we call it today- wetlands). If honey bees were taking over all of the suitable nesting cavities in trees, where was the impact to other birds, including woodpeckers?

Perhaps future researchers will find a collected specimen still hosting a deadly virus or non-native mite that points to their extinction.

Will we ever again encounter a living Carolina parakeet?

Starting at age 12, I’ve often daydreamed of opening a newspaper and reading that a small flock of Carolina parakeets were found in a remote corner of the Everglades. Or maybe a brilliant scientist cloned a museum specimen. Unfortunately, it hasn’t happened so far.

I still get a little ticked off remembering the night of April 1, 2009, when a prankster posted a fake article stating that the Carolina parakeet was rediscovered. I’ll blame it on it being 2:00am when I read the story on the internet (an example of my obsession with extinct animals), but I should have noticed that Carolina parakeets had ivory colored bills and the photograph in question showed a parrot with a black bill.

 

 

Anyway, no matter how many hours I spend googling “Carolina parakeet rediscovered” nothing of value ever turns up. However on any given week, you’ll find an article or blog claiming that a thylacine, ivory-billed woodpecker or passenger pigeon was photographed or videotaped, but by the end of the article you’re always presented with a blurry photo.

Why is it that there never seems to be even the remotest hint of a living Carolina parakeet? My belief is that each of the animals I’ve mentioned can easily be a case of mistaken identity. A thylacine looks a lot like a coyote with mange. An ivory-billed woodpecker looks very similar to a pileated woodpecker. Even the passenger pigeon can be mistaken for a discolored mourning dove. However, there are no other native parrots to be found in the eastern US. The only parrots that are living in the wild today are feral birds found in the suburbs eating from bird feeders. You’re not going to find a sun conure, for example, in the middle of a swamp in Arkansas.

If we woke up tomorrow morning to a report of a living Carolina parakeet, where would they have been found? I’m of the opinion that the U.S. is out of the equation. However, maybe some existed in Cuba outside of their known historic range. Perhaps deep in a swamp lives a small population of birds that blends in with the other native parrots on the island. Very doubtful of course, but it gives me some hope.

What about cloning?

Dolly the sheep started it all in 1996, when scientists in Scotland announced the first cloning of a mammal. Early reports discussed how this new technology was going to revolutionize science as we know it. Disease resistant humans with an average IQ of 150 were right around the corner. Get ready for mammoths and dodo birds at your local zoo. Everything was going to change.

Twenty-one years on and still no mammoths. The number of cloned animal species is short. The closest we’ve come to cloning an extinct animal was using frozen DNA from a Spanish ibex subspecies to produce a clone that lived for several hours and some gastric brooding frog eggs that divided a handful of times before stopping.

On any given day, you can google “extinct clone” and read about a scientist claiming that a living mammoth will be born in the next 3-5 years. But it never happens.

In my non-scientific understanding (I’m an engineer that got a B- in biology), we’re probably decades away from bringing back the Carolina parakeet. Cloning extinct animals still has too many barriers that need to be overcome. Ten years from now, we may read about the insertion of sections of DNA from a black footed ferret museum specimen into the cells of a living ferret to enhance this species diversity. Or maybe several sections of a heath hen’s DNA are inserted into a close relative to create a hybrid specimen that looks and acts somewhat like an actual heath hen.

The closest relatives to Carolina parakeets are conures living hundreds of mile away in South America. But, they’re probably more distantly related to the Carolina parakeet than we are from Neanderthals. It’s very unlikely that we can currently insert sections of Carolina parakeet DNA into a sun conure to produce an almost pure Carolina parakeet. Even if we had a complete section of DNA, they’re probably too distantly related to make it work.

If not cloning, are there other options?

I’ve read on several occasions that two different species of conures were cross-breed to create a bird that looks a lot like a Carolina parakeet, however they’ve never included a photo of the bird.

 What if a mitred conure was cross-bred with a jandaya conure?

 

 After a number of attempts, you may be able to produce an offspring that includes the ivory colored bill and red face of the mitred conure with the red and yellow facial patterns of the jandaya conure. By no means would this hybrid be capable of living in the same habitat as a Carolina parakeet, but perhaps down the road soft releases could be made in Charleston, South Carolina as a tourist attraction similarly to the parrots of San Francisco.

Once we have this pseudo-Carolina parakeet available to scientists, at some point they could begin to insert small sections of Carolina parakeets DNA into them to produce parrots that behave more like the actual bird. These new birds could then be introduced into Carolina parakeet habitat.

Photographs and video of living Carolina parakeets

I’ve always been surprised that so few photographs of a living Carolina parakeets exist as I’ve only been able to locate two photos. In addition, I’ve read on multiple occasions that “someone” has a color video of a possible flock of Carolina parakeets taken in Florida sometime between the late 1930s to early 1950s. Despite many attempts to find this video, I’ve had no luck.

I’m really surprised that no photos have been found of the last known Carolina parakeet (Incas) living in the Cincinnati Zoo before they went extinct in 1918. Surely, in some drawer is a good, detailed photo of the bird.

Below is a photograph of a pet Carolina parakeet.

 

I couldn’t find a free copy of the second photograph, but it’s a poor quality photo of a bird sitting on a branch in front of a solid background. You really have to spend a lot of time looking on Google to find this example.

American Chestnut Tree

The story of the American chestnut is well known to the people of Appalachia listening to stories told by their grandparents and great-grandparents. This tree, once called the redwood of the east coast, could grow eight feet in diameter and stretch 120 feet in height. Chestnuts trees were so productive, seeds from a single tree could sustain a pioneer family through a harsh winter.  Timber cut from the tree could last 100 years without rotting. From these reason and many more, the American chestnut was considered the most valuable tree in the eastern forest.

 

Beginning in the early 1900s, American chestnut trees in New York City began to die off in mass. The culprit was a pathogenic fungus (Cryphonectria parasitica) from eastern Asia that entered the trees through small cracks in the bark. Once infected, cankers would form around the trunk of the trees starving the tree of nutrients. They would then die off over a period of several months, surviving only within the root systems. Suckers would grow from the tree roots only to succumb again to the fungus before the trees reached 20 feet in height. Considering that American Chestnuts will only produce nuts when the trees reaches 20 feet in height and around 8 years in age, chestnuts seeds were completely eliminated from our forests in under a generation.

 

Fortunately, large chestnut trees planted outside of their original range can still be found. I’ve found multiple articles describing large chestnut trees from Oregon to British Columbia. Whether this is due to the fungus never being introduced to this part of the country or to the mild weather and soil conditions, their survival in the Northwest is not fully understood.

Outside of a few dozen trees surviving through a combination of luck, blight resistance, and hypovirus (a blight that kills the chestnut blight) the American chestnut tree was lost from the east coast. These remaining trees are now being used by researchers to develop blight resistant trees that could one day be introduced back into our forests.

Strategies for the Future:

Scientists are proceeding with three separate strategies to bring back the American chestnut tree. The first is to cross-breed the surviving pure American trees to produce future generations of trees with greater resistance to the chestnut blight. The second effort started by crossing an American chestnut tree with a naturally disease resistant Asian Chestnut tree to produce offspring that look like an American Chestnut tree while offering protection from the fungus. The third and most recent effort uses cutting-edge science to insert a wheat gene into chestnut trees to produce a tree that can fully resist the chestnut fungus.

I’m going to offer my opinion on each strategy from a non-scientific position (I’m an engineer) to discuss what the future may hold for each team of researchers.

The obvious strategy is to find surviving American chestnut trees that then can be cross-bred to develop trees that offer more resistance than their parents. Breeding these resistant trees with each other over several generations will hopefully produce an American chestnut with nearly the same blight resistance as an Asian chestnut. While this may appear to be a no-brainer, it actually requires the most amount of effort to complete.  The American Chestnut Cooperators Foundation is leading this effort through a nonprofit scientific and educational foundation formed by researchers from Virginia Tech’s Department of Plant Pathology, Physiology & Weed Research, as well as, scientists from Concord College in West Virginia.

Beginning in the 1970s, the foundation has worked with the public to identify large, surviving trees. A male catkin pollen is collected from an American chestnut to then pollenate a female flower from a second surviving American chestnut. The seeds are then collected in the fall to be distributed to volunteers that grow and monitor the offspring. The best trees are then cross-bred to other disease resistant trees for several generations (I believe that they’re up to the 6^th generation of trees).

Their website is http://www.accf-online.org/ but it’s infrequently updated. In addition, they don’t go into great detail as to the survivability of the 6^th generation trees, only stating that they may express some disease resistance. What this means is difficult to understand. My guess is that the even their best trees may only live for 30-50 years before succumbing to the fungus, instead of living to 200-300 years as the trees did prior to the 1900s. Either way, they’re making a great effort that should eventually pay off.

The American Chestnut Foundation is a nonprofit team founded in 1983 by a group of scientist in Virginia. This team initially cross-bred an American Chestnut with a blight resistant Asian chestnut to produce a descendant that could fight off the chestnut fungus while exhibiting some American chestnut features.  Trees showing good resistance were then back-crossed with pure American Chestnuts to produce trees that were 75% American Chestnuts and 25% Asian Chestnut.

Back-crossing for several more generations produced the current tree that is 15/16 American chestnut and 1/16 Asian chestnut. These trees exhibit the look and form of an American chestnut while still having the blight resistance of an Asian chestnut. Considering that an American chestnut contains around 100,000 genes, these 15/16 American chestnut trees include over 6,300 Asian chestnut genes, some of which may be counterproductive to the ACF’s efforts.

 

While it would make sense to a layman that they should continue to back-cross for several more generations to eliminate more of these unwanted genes, the American Chestnut Foundation appears to be focusing on introducing these 93.5% American chestnuts into our forests. It may be that the trees look just like a pure American chestnut, so their efforts would be better spent on reintroducing this tree back into our forests.

It’s important to note that the while the American chestnut and Asian chestnut trees are cousins, their adult forms are quite different. As stated earlier, an American chestnut tree can grow up to 120 feet in height and live for 200 to 300 years. On the other hand, an Asian chestnut tree is more similar to an apple tree in that they only grow 20 to 30 feet tall and live 50 to 75 years.

I would like to learn from the American Chestnut Foundation whether they believe these disease resistant trees are expected to mature like an all-natural American chestnut or produce a tree midway between the American and Asian chestnut. Maybe the goal for these trees is for them to reach 75 feet in height and live 100 years.

The American Chestnut Foundation has a really good website that is updated frequently. They can be found at www.acf.org.

The last and most recent effort is to insert non-chestnut genes into a pure American chestnut to limit the growth of the chestnut blight.

The American Chestnut Foundation is also working with the State University of New York, College of Envornmental Science and Forestry (SUNY-ESF) to insert individual genes into an American Chestnut tree to enhance pathogen resistance using the tools of genetic engineer.

The science behind this effort is over my head, but is still interesting. Typically, when a powerful medicine is found to treat illnesses (ie penicillin), over many generations, the disease begins to build resistance and eventually fully overcomes science’s best efforts to eliminate it. The ACF is using a different strategy to address this problem.

Native Range Map

 

Using biotechnology, scientists have inserted a wheat gene called Oxalate Oxidase to break down the oxalic acid found in the blight fungus. Instead of killing the chestnut blight, this gene will instead deactivate the fungus, preventing it from killing the chestnut. As this gene does not force the fungus to breed for resistance, scientist expects that future generations of chestnut trees with this gene will continue to prevail against the blight.

Considering that inserting a gene from wheat into a tree requires government approval, the release of this tree to the public could still be 10 to 20 years away. To address this problem, the ACF has is growing 10,000 transgenic trees with the hope that they can get a jumpstart once/if the USDA signs off on this process.

In my opinion, this plan offers the greatest opportunity to allow future generations to see a 300 year old American chestnut producing nuts for bears, wild turkeys and and maybe even pseudo-passenger pigeons (more on that on another blog) into our forests. On the downside, any mention of genetic engineering will create an outcry from the public. Scientists are experiencing this in Key West, Florida as I write. Their plan to release transgenic mosquitoes to fight off the deadly Dengue fever threatening public health. While spraying mosquitoes with deadly chemicals is okay with the public anything hinting at genetically alternated insects is feared.

Other Items:

For years, everything I’ve read about the loss of the American chestnut only concerned the chestnut blight killing trees found at higher elevations in the Appalachians. However, I recently learned about another chestnut disease that killed off chestnut trees living at lower elevations in the early 1700s.

The American Chestnut Foundation’s website discusses Phytophthora cinnamomi which is a virulent pathogen of the American chestnut tree that causes the disease Phytophthora (otherwise known as “root rot”).

Apparently, the American chestnut tree had a range extending beyond the Appalachian Mountains down to the Gulf of Mexico, east to the low county of South Carolina and north along the entire east coast. Because this disease quickly killed off low elevation chestnut trees hundreds of years ago, scientist only recently learned that there was a second disease capable of killing the chestnut tree.

From my understanding, Clemson University in partnership with North Carolina University and the US Forest Services, learned about this additional disease when disease-resistant American chestnut trees quickly died off when planted in coastal South Carolina.

As the Asian chestnut tree also has resistance to this second disease, it is expected that protection from Phytophthora cinnamomi can be quickly established in the American chestnut.