Post-Extinction Consequences of Passenger Pigeon on Forest Ecosystem

There was a time that the forests of Eastern North America were very different than they are today. A thick, endless canopy stretched from the Southeastern United States northward well into Canada. Oaks, Birch, Beech, Sycamore, Bur and American chestnut were a few of the trees that comprised this great forest. Within this forest one could see black bear, deer, squirrels, wood rats, plethodontid (lung less) salamanders and even the now extinct heath hen (1). Massive flocks of passenger Pigeons could be seen roosting in this canopy in such numbers that the limbs of trees often broke off or entire trees toppled from the weight. I will be focusing this essay on this last creature’s effect on the ecosystem both before and after its demise, lonely at the Cincinnati Zoo, in 1914.

The social bird was so abundant (total population aprox. 3-5 billion individuals) that flocks could be seen in the sky as large as 1 km wide and 400-450 km long. This did not only affect the umbrella industry but also the entire forest ecosystem. The amount of mast consumed by these creatures may have been as large as 210 million L per day for a population of 3 billion birds. That makes for a lot of excrement. In fact, several inches of feces could accumulate on the forest floor underneath a medium to large sized roost. Not only did all this excrement kill understory vegetation it also produced an enormous amount of fuel for wildfires that periodically swept through. Combined with the dead wood from all the broken limbs caused by the roosts one can imagine the fires must have gotten pretty serious.

These large fires would have favored the more resistant white oak, black oak and bur while removing the less resistant trees. This was great for the pigeons as they ate quite a lot of white oak acorns during mating season. This was great for the white oaks because the acorns, processed and excreted by the pigeons, germinated and led to more white oaks (2). Yes, it appears the Passenger Pigeon had quite an effect on the forest ecosystem.

By 1914, with the passing of the last Passenger Pigeon, all of the effects the bird had on the ecosystem were now eliminated. The canopy damage done at the birds roosting sites had allowed more shade intolerant plants to come in and mature in the areas with more light hitting the forest floor while the birds were still alive. This effect has been magnified (though not due to the birds demise) with the loss of a large portion of their habitat through chestnut blight. Now, in the post extinction world, we see a larger amount of these shade intolerant trees filling the gaps.

With the large flocks gone from the forest, the massive amount of mast consumed has had more of a chance to fill in the space once covered in excrement. That’s great for some species of tree like the red oak which has come in to fill in areas once dominated by the now ungerminated white oaks. And what about all the excrement created by all that consumption? Without it around, plants are now able to grow where they were once killed by excess amounts of feces. Nor can that excrement any longer fuel fire intensity. Thus, the ability for less fire resistant plant species to reach maturity has greatly increased. Of course, fire suppression by humans has also aided the less resistant trees in this manner.

In conclusion, one can clearly see that the extinction of the Passenger Pigeon has left a lot of gaps in what the forest ecosystem once was. Fortunately, there have been many things to come in and fill those gaps. As the gaps have been filled in by very different mechanisms it can be concluded that the forest ecosystem of Eastern North America will never again be the same as it was in the days when giant flocks of Passenger Pigeons darkened the entire sky.

References cited

1) Lord, William. “Wildlife Food: The Pre-blight chestnut and the post-blight acorn.” The Journal of the American Chestnut Foundation. vol XIX no.1 (2005) 29-32

2) Ellsworth, Joshua W. & McComb, Brenda C. “Potential Effects of Passenger Pigeon Flocks on the Structure and Composition of Presettlement Forests of Eastern North America.” Conservation Biology. vol. 17 no. 6 (Dec. 2003) 1548-1558

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