Mr. Kimmerle
We got into a discussion on another thread about pre-historic purple martin population density. You wrote an impressive argument that martin populations prior to European settlement in North America may have been lower than today, because of continuous forest.
All this prompted by me dredging up a statement from somewhere that current populations may be only a fraction (one-tenth maybe) of levels prior to introduction of English House Sparrows and Starlings in 1800s.
Question: Isn't it feasible that martin populations actually peaked in the 1800s, at significantly higher levels than today, due to clearing of land and martin housing provided, free of foreign bird competition, by folks at the time?
John Miller,
St. Louis, Mo
Question for K. Kimmerle
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Guest
I wasn't specifically saying that population levels would have been lower pre-settlement, just that it is unrealistic to think that population levels were hundreds of times larger than they are today given the species' core habitat requirements.
There are two primary factors you need to consider - when the mass deforestation occurred; and the species ability to fill a niche once suitable is made available.
Generally speaking, deforestation of the eastern deciduous forest began in the northeast and worked its way to the southwestern regions of the forest. While settlers began clearing the forest primarily for small-scale farming purposes well before 1850, it was mechanized large-scale farming during the early 1900s that resulted in the opening of very large land-tracts. Farmers that were required to use horse-drawn plows and hand-harvesting prior to the arrival of motorized farm equipment simply could not farm the hundreds of acres per individual they can today.
If you go back and read more of Audubon's writings, you will find his numerous comments on the grandeur and extent of the hardwood and pine forests that still covered much of eastern North America during his time.
But even if the extent of deforestation was similar to today, a species' ability to respond to such an ecological release is driven largely by the species' population dynamics, not solely by the amount of suitable habitat at any one given time. In simplistic terms, if Purple Martins did not have to content with predators, parasites, exotics, and the many other factors they do today (and did back then as well), doubling the amount of suitable habitat this year would not result in a doubling of population numbers the following year. This (population growth) is driven by population dynamics such as the rate of survival, reproductive rate, food availability, weather and a host of other limiting factors. A population that has an intrinsic growth rate of one-percent per year will take 72 years to double in size.
An excellent example of this is recovery of endangered species. The Critical Habitat provisions of the Act are currently under fire, because law-makers fail to see why many species aren't flourishing. First, populations and the critical habitat they depend upon don't recover overnight from decades of abuse. When we look at those species that have successfully recovered as a result of the Act, they are almost all tied to DDT. We're just now starting to see some of these species' delisted after more than 30 years of banning *all* use of DDT, not just simply banning DDT's use in areas where the affected species population ranges have retracted to.
How can we realistically expect species to recover when we apply a piece-meal approach of saving some critical habitat and then only in those areas were the species is still hanging-on. How does a species recolonize habitat that no longer exists. How do you expect a species to recover to historic population levels, when suitable habitat is not available throughout their entire historic range? Reintroduction and recolonization are long-term process even when suitable habitat is already present.
And even if many people provided martin housing in the 1800's, how much of this reproductive effort represented the tradition shift to man-made housing, versus filling this new niche in addition to continued breeding in their [then] traditional breeding niche in natural snag cavities?
Also consider that the deforestation occurred at about the same time as the introduction of the European Starling (EUST) and House Sparrow (HOSP). While the introduction of the EUST stemmed from 2-3 releases in the 1850s, HOSPs were released by European settlers throughout the U.S. over a long period of time, as many HOSPs were brought over as cage birds by immigrants entering this country.
There are two primary factors you need to consider - when the mass deforestation occurred; and the species ability to fill a niche once suitable is made available.
Generally speaking, deforestation of the eastern deciduous forest began in the northeast and worked its way to the southwestern regions of the forest. While settlers began clearing the forest primarily for small-scale farming purposes well before 1850, it was mechanized large-scale farming during the early 1900s that resulted in the opening of very large land-tracts. Farmers that were required to use horse-drawn plows and hand-harvesting prior to the arrival of motorized farm equipment simply could not farm the hundreds of acres per individual they can today.
If you go back and read more of Audubon's writings, you will find his numerous comments on the grandeur and extent of the hardwood and pine forests that still covered much of eastern North America during his time.
But even if the extent of deforestation was similar to today, a species' ability to respond to such an ecological release is driven largely by the species' population dynamics, not solely by the amount of suitable habitat at any one given time. In simplistic terms, if Purple Martins did not have to content with predators, parasites, exotics, and the many other factors they do today (and did back then as well), doubling the amount of suitable habitat this year would not result in a doubling of population numbers the following year. This (population growth) is driven by population dynamics such as the rate of survival, reproductive rate, food availability, weather and a host of other limiting factors. A population that has an intrinsic growth rate of one-percent per year will take 72 years to double in size.
An excellent example of this is recovery of endangered species. The Critical Habitat provisions of the Act are currently under fire, because law-makers fail to see why many species aren't flourishing. First, populations and the critical habitat they depend upon don't recover overnight from decades of abuse. When we look at those species that have successfully recovered as a result of the Act, they are almost all tied to DDT. We're just now starting to see some of these species' delisted after more than 30 years of banning *all* use of DDT, not just simply banning DDT's use in areas where the affected species population ranges have retracted to.
How can we realistically expect species to recover when we apply a piece-meal approach of saving some critical habitat and then only in those areas were the species is still hanging-on. How does a species recolonize habitat that no longer exists. How do you expect a species to recover to historic population levels, when suitable habitat is not available throughout their entire historic range? Reintroduction and recolonization are long-term process even when suitable habitat is already present.
And even if many people provided martin housing in the 1800's, how much of this reproductive effort represented the tradition shift to man-made housing, versus filling this new niche in addition to continued breeding in their [then] traditional breeding niche in natural snag cavities?
Also consider that the deforestation occurred at about the same time as the introduction of the European Starling (EUST) and House Sparrow (HOSP). While the introduction of the EUST stemmed from 2-3 releases in the 1850s, HOSPs were released by European settlers throughout the U.S. over a long period of time, as many HOSPs were brought over as cage birds by immigrants entering this country.
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John Miller
- Posts: 4866
- Joined: Mon Mar 22, 2004 9:11 pm
- Location: St. Louis, MO
Hey Keith
Thanks for your insight. Your rationale makes sense, that much of the eastern landscape was still so heavily forested in the mid 1800's that it might not have hosted any more martins than we have today.
Still, in my home state of Kentucky, many rural counties had about the same 10,000 or so human population in about 1850 as they do today. (later many moved West, especially to Texas, so maybe Laverne, Emil and I are all kin). Most of these folks lived on small farms and certainly cleared enough land for tobacco and food crops. The human population actually was more scattered than today, with many little villages whose names still appear on maps but actually are now gone. There were no vast soybean and corn fields, but surely many open pockets, and I can't help but suspect it was pretty good martin habitat: few EH sparrows, no starlings and I'm assuming a strong tradition of putting up martin housing.
I find your conclusions in another thread that today's landscape could likely support a much larger martin population to be very encouraging. So let's get more folks interested in pursuing this wonderful hobby and in doing it right. The more martins the better.
John Miller,
St. Louis, Mo
Thanks for your insight. Your rationale makes sense, that much of the eastern landscape was still so heavily forested in the mid 1800's that it might not have hosted any more martins than we have today.
Still, in my home state of Kentucky, many rural counties had about the same 10,000 or so human population in about 1850 as they do today. (later many moved West, especially to Texas, so maybe Laverne, Emil and I are all kin). Most of these folks lived on small farms and certainly cleared enough land for tobacco and food crops. The human population actually was more scattered than today, with many little villages whose names still appear on maps but actually are now gone. There were no vast soybean and corn fields, but surely many open pockets, and I can't help but suspect it was pretty good martin habitat: few EH sparrows, no starlings and I'm assuming a strong tradition of putting up martin housing.
I find your conclusions in another thread that today's landscape could likely support a much larger martin population to be very encouraging. So let's get more folks interested in pursuing this wonderful hobby and in doing it right. The more martins the better.
John Miller,
St. Louis, Mo
I "think" some species can and do take over. A good example is killer bee's. What is one man's good idea is other regret. The Aussie's have had several trans-planted animals produce twenty fold in a few short years. Natural or man transplanted no one really can know the results until years later if then. A good example of that is the clouds of starlings you see across this country and Canada. Even with hundreds of cities trying to reduce there population they still continue to breed like rats. Speaking of Rats?????
Another good example is a spider that's made it's way from Asia through shipping that's spreading across from US from the west. Looks like Brown Recluse, but it bit is worst. So the pecking order of worse spider to be bitten by has changed. Anybody know it's name? I was bitten by a orb weaver spider a few weeks ago, so I was reading up on spiders. A spider that's suspose to be harmless! I guess if you don't die or you arm rot off it's considered harmless. That wasn't the word I would use to describe it after the Volcano looking pit that was left in my arm after a few weeks of ozzing yellow mucky stuff. Another common house spider you don't want to be bit by is the Funnel web spider!
Another good example is a spider that's made it's way from Asia through shipping that's spreading across from US from the west. Looks like Brown Recluse, but it bit is worst. So the pecking order of worse spider to be bitten by has changed. Anybody know it's name? I was bitten by a orb weaver spider a few weeks ago, so I was reading up on spiders. A spider that's suspose to be harmless! I guess if you don't die or you arm rot off it's considered harmless. That wasn't the word I would use to describe it after the Volcano looking pit that was left in my arm after a few weeks of ozzing yellow mucky stuff. Another common house spider you don't want to be bit by is the Funnel web spider!