LISTSERV 16.5 - GRC Archives

re: Population declines of eastern indigo snakes (Drymarchon couperi) over three decades in the Gulf Hammock wildlife management area, Florida, USA by J. Steve Godley and Paul E. Moler (Copy here attached)

Thanks for bringing this paper to my attention. This study, if one may call it such, only confirms the obvious. The sample sizes are too small for the results to be of any significance other than to indicate an undeniable trend toward extinction. Several of the assertions need to be challenged.

let me begin with the presumption, common among herpers of a certain age and explicit in this paper, that many once common herp species prefer disturbed habitats. If that were true there would be more herps than ever, especially wide ranging generalist species such indigos and kingsnakes.

As you know, kingsnakes though largely extirpated today were until recently found from the Atlantic to the Pacific and everywhere in between except for the driest deserts and the coldest mountaintops. Unlike indigos which have large home ranges and are thus greatly subject to road mortality kingsnakes were until recently capable of living in densely populated areas. Nevertheless, they are now gone. The bottom line is that climate and biogeographical history are the only constraints to the range of either Drymarchon or Lampropeltis.

Past "studies" have indicated that indigos require gopher holes for shelter but nothing could be further from the truth, they are neither habitat nor prey specific and prior to their decline could be found anywhere throughout their range eating whatever they could stuff into their mouths. Over the course of my herping career I have been privileged to have seen quite a few Drymarchon here in Florida, in Texas, in Mexico, and especially in Belize where they are one of the most common snake species. Within their range they may be found in virtually every habitat from seashore to mountaintop, from marshlands to savanna to the deepest jungle. Having said that the preponderance of my observations have been made in undisturbed or relatively undisturbed habitats. That is especially true of large individuals. Nowhere is that more true than in Gulf Hammock which was for the most part forest primeval until the 1970s and was full of big indigos.

Moler's observation that indigos in Gulf Hammock preferentially occupied ten year old clearcuts is misleading. Disturbed and especially edge habitats often experience a temporary increase in biological productivity that can be exploited by top trophic level species like indigos. It does not follow that these peripheral feeding areas are somehow more important to the species than the core habitats to which they are primarily adapted. For example, in late summer timber rattlesnakes often utilize the edges of farmer's fields at the foot of the mountains that are their core habitat. Does it follow that farm fields are more important than hibernacula? Grain farming produces an unnaturally high concentration of rodents yet rattlesnakes continue to decline everywhere except where large areas of core habitat are protected. Unless I am mistaken both indigos and rattlesnakes were doing quite well prior to 1492 despite a lack of disturbed habitats and heavy predation by indigenous Americans.

Sampling bias also leads to the false impression that anthropogenic disturbance is somehow good for herps. Old herpers such as ourselves fondly remember the days when flipping a piece of tin would often turn up a snake. Try it today and all you will find are a few fire ants. That is even true in those rare instances where an old house with tin abuts a protected core habitat. It is tempting to blame the fire ants, or a combination of all other such factors such as habitat destruction, road mortality, etc, but none or even all of those factors can fully explain the decline. More on that in a moment.

The most common form of herp census, and the primary method used in this study, is by means of road cruising which can lead to false conclusions. The roads in Gulf Hammock predominantly pass through clearcuts. That is why the roads were built in the first place, to destroy the forest. Only rarely do the roads pass through significant stretches of undisturbed forest except in the case of deep swamps. Indigos will live in swamps but it is not their preferred habitat so it should not be surprising that the majority of specimens are found on stretches of road surrounded by ruined habitat.

It is often said that it is difficult to find snakes in the jungle and that is true. Ecotourists can wander for weeks in the rainforest and never see a snake. But build a new road through undisturbed rainforest and presto snakes cover the road until the inevitable decline due to road mortality. Should we suppose that the sudden increase in snake observations means that roads are the preferred habitat of snakes? It is all a matter of sampling bias.

The most egregious error in this report is the assertion that, "environmental pollution, disease, and climate change seem to be insignificant or discountable factors at this site". I would agree that pollution and climate change are negligible factors. There is little or no pollution in Gulf Hammock, and climate change should if anything be of benefit to the indigo which is a predominantly tropical genus.

There is no reason whatsoever for the authors to assert that disease is not a factor. They offer no explanation for this position for the simple reason that they have no information. Lack of evidence is not evidence of lack. They have no information because when a snake gets sick it crawls into a hole and dies never to be seen again. It is very difficult to study epizootic incidents in cryptic species because you can't study what you cannot see, but there is an ever increasing body of indirect and anecdotal evidence that points to invasive pandemics as the underlying cause of reptile decline not only in Gulf Hammock but throughout the world.

There is no denying that the "usual suspects" such as habitat destruction, road mortality, direct persecution, pollution, climate change, and fire ants all contribute to the decline, but not even the sum of these factors can explain the sudden widespread disappearance of otherwise successful generalist species throughout their range.

Frogs and turtles are much more easily studied than snakes and so there has been a recent avalanche of empirical evidence that both of these groups have been devastated by several recently emerged pandemic diseases spread initially by anthropogenic means.

As you know, I am interested in the possibility that Ranavirus may be one of the primary culprits in the overall decline of our herpetofauna. It is a devastating disease to which almost all exothermic taxa are susceptible to some degree. I know from personal experience that in turtles it spreads rapidly, has a very high mortality rate, and can kill susceptible individuals within a week. You are highly unlikely to find a snake in the field which is suffering from such a virulent disease. It will either be uninfected or dead, a moldering line of vertebrae somewhere in a hole in the ground.

It is worthy of note that both indigos and kingsnakes are primarily ophiophagous species that eat other snakes that eat frogs, some species of which such as bullfrogs are relatively resistant to Ranavirus and have been shown to carry the disease. Likewise, it is worthy of note that those species such as rattlesnakes that are primarily rodentivores have been less affected by mass die offs despite the impact of habitat destruction and direct persecution.

I am a field naturalist not a scientist per se, so I cannot say with any certainty that Ranavirus is the primary factor in the decline of indigo snakes in Gulf Hammock but I strongly suspect that it is. One should not conclude from this that other pathogens, land management practices, or environmental factors are not involved.

Mr. Godley is an environmental consultant who works closely with the phosphate industry and other development and resource extraction industries. He was instrumental in preparing the biological inventory and other such reports necessary for the permitting of the King Road Mine in Gulf Hammock, a project which will further fragment and destroy what little is left of Gulf Hammock’s original forest ecosystem. Mr. Godley knows what side his bread is buttered on.

It is a sorry fact that throughout the nation the integrity of the environmental consulting industry has declined faster than the ecosystems they purport to study. They are bought and paid for either by industries that require permits and are loathe to see results that might negatively affect their projects, or by governmental bureaucracies that seek to maintain the status quo for political reasons. Such is the case with the ill named Florida Fish and Wildlife Conservation Commission which has muzzled its finest scientists throughout their careers. In either government or industry if you rock the boat you are out the door.

Some say that advocacy has no place in science but I disagree. Should we respect the opinions of climate change denialists simply because the data are inconclusive and they are doing their jobs on behalf of their masters? What about those who study dying ecosystems and come to no conclusions other than that we need more studies (for which they get paid)? When I see a bug stop a future pipeline I might change my tune, but the days of the snail darter are gone. In a time of diminishing resources business always wins.

Other than small private inholdings, many of which contain the last remaining patches of original forest, the entirety of Gulf Hammock should be confiscated by the government and those responsible for the environmental crimes should be imprisoned. Their sentences could be reduced through the provision of field labor necessary for the ecosystem restoration program. For example, the CEO of Georgia Pacific could get a one hour reduction in his sentence for every Monsanto brand pine tree he cuts down with a rusty hatchet. (I’m channeling Pol Pot here.)

The good news is that the destruction of Gulf Hammock is a relatively recent event so the germs of life remain in the seed bank. Likewise, a small amount of intact hammock remains in the nearby Waccasassa Bay State Preserve. In a few hundred years all should be well provided that the whole place has not been submerged by rising sea levels.

Meanwhile back at the lab leading scientists such as Paul Moler could be working on reintroduction programs rather than just documenting declines. I just said that there is no foreseeable cure for an epizootic event once the cat is out of the bag but that is not necessarily true in the long run. All diseases either die out or coevolve with their hosts through a lessening of virulence. Even such plagues as water hyacinth and fire ants are slowly coming into “balance”. The problem is that coevolution cannot happen if the host is missing. Therein lies the value of reintroduction programs no matter how hopeless they may seem at first. All you can do is try. Without such efforts there is no hope whatsoever because extinction is forever. As for keystone creature such as bears and panthers all they need is a little boost and a lack of bullets.

So I reject the paper’s finding that the cause(s) of indigo snake decline in Gulf Hammock are unknown and that nothing can be done. Meanwhile I will cherish the memory of a giant indigo glistening in the winter sun along Spring run in what used to be Gulf Hammock.