Sunday, September 27, 2009

You are what you eat

What does an animal eat? It’s perhaps the most basic question a biologist can ask. Knowing what a species consumes is critical to understanding to how relates to its habitat and the ecosystem. Sometimes, these secrets are readily revealed.

Many snakes, when disturbed, will be all too happy to divulge their last meal by presenting you with a fresh regurgitation of partially-digested creature. Maybe these snakes feel they will be able to flee more rapidly with an empty stomach. On the other hand, perhaps this encourages potential predators to find something else to eat, something that smells a little more appetizing.

Snakes are famous for constricting their prey, I’m sure many people have nightmares of a large specimen wrapped around them. But, lots of snakes in our area don’t constrict at all, they simply grab prey in their mouth and start swallowing. Their bottom jaw is made of two different bones which they manipulate to swallow large prey and work it down their throat. As you may imagine, this is likely an unpleasant experience for the hapless prey, which, as they’ve not been constricted, are swallowed alive.

On these occasions, a frightened snake could mean good news for its last meal. Hognose snakes are famous for their defensive displays, which often includes throwing up. They are also fearsome toad hunters, these amphibians are their primary prey. It is not unusual to find a bloated hognose snake that will freely cough up a live toad with only the slightest provocation. This toad, perhaps after a flustered moment, will eagerly take the opportunity to hop away, and perhaps will be more cautious the next time a serpentine shape approaches. I recently worked in a lab in southwest Georgia that kept a toad as a pet for years after a recently captured hognose snake gave him a second chance at life. A hognose snake I recently captured coughed up a live spadefoot toad that weighed more than it did!

Snakes don’t always make it that easy for you, however, and traditional methods of determining snake diet don’t present very appealing options. Typically, when a researcher finds a snake with a tell-tale bulge in its body, the snake can be coerced into regurgitating its prey by pressing a thumb against its body and working the prey item out of its mouth. In the best case scenario, the researcher now has a recently ingested prey item that allows for easy identification. What is more likely, however, is that an odorous warm glop will appear, a glop that defies classification. In both cases, the snake loses its meal. For an animal that doesn’t eat often, a forced regurgitation may have unintended consequences to its long-term health.

But, it’s better than the other typical method. If you were to peruse some classic snake ecology papers, you’ll quickly realize that thousands of snakes have given their lives so that we can better understand their natural history. One of my goals is to advance our understanding of snakes without sacrificing them in the process. If you’ve watched any of the number of crime shows on television, you know that researchers can often find DNA from the most unusual sources. Although the methods are often dramatized on the television, some of the concepts are grounded in real science.

You are what you eat, right? When I catch a snake, I hold it in a cage until it provides a scat sample and I preserve this scat sample in alcohol or acetone. The goal is to take these samples into the lab and subject them to a long and complicated process with the goal of extracting any present DNA. These small fragments of DNA are then exposed to other strands of DNA in the hopes of kickstarting their replication. Different species have different and unique strands of DNA; these strands are made of base pairs (if I mentioned adenine, thymine, cytosine, and guanine, does it bring you back to your high school biology class?). When the DNA has replicated, we can examine the unique sequence of base pairs in the product and determine what unlucky species had been eaten by the snake.

It’s expensive, time-consuming, and requires additional testing before it’s accepted as a legitimate methodology, but I hope this technique changes the way we study and learn about snakes. Ideally, it will be more accurate than sorting through a glop of vomit, less intrusive than forced regurgitation, and no snakes will be killed in the process.

Sometimes snakes make it easy for you. Here's a recently captured hognose snake that coughed up a partially digested frog. There was enough left to identify it as a southern leopard frog. Photo courtesy of Michelle Baragona.

Thursday, September 24, 2009

Big Snake in Newark, Delaware

Each morning I get sent recent articles pertaining to snakes, turtles, and similar creatures in the news. Some reflect just how detached we've become from the flora and fauna that surround us.

Although this blog generally pertains to southeastern wildlife, I can't resist commenting on an article I received about a giant snake on the loose in Newark, Delaware. On Friday afternoon, a couple kids took a picture of a large snake crawling in a tree near their house. Later they told their mom that they had seen a "black snake", this is one of the common names generally used for the Eastern Rat Snake (formerly Black Rat Snake), Pantherophis alleghaniensis. Here in the southeast, we have a closely related species, the Gray Rat Snake, Pantherophis spiloides.

In any case, that should have been the end of it.

The mother, amazed at how large the snake looked in the pictures, proclaimed that this could be no native snake. Local officials "confirmed" that this was likely an escaped python or boa constrictor, perhaps 8-10 feet long. Neighbors were warned of the potentially dangerous animals roaming their streets and backyards and were encouraged to keep their children and pets under close supervision.

The kids were correct. This is not an exotic snake. This is not a dangerous animal. What they saw was a rat snake. Granted, a large individual can surely be a shock to the system as it's true that some can reach in excess of eight feet. This makes them one of the largest snakes native to North America, but they are harmless, unless you're a squirrel or rat.

Rat snakes have well-developed climbing abilities and are often found crawling through tree branches in search of birds or a secluded place to rest. Given that fall is advancing, it's possible that this snake was looking for somewhere safe to spend the winter, or maybe a final meal before it commences hibernation. These snakes can be common in suitable conditions, but not necessarily frequently encountered. This may explain the odd behavior exhibited by the adults involved in its identification and subsequent warnings. I'll grant them that it may not be easy to identify the snake from the one available picture given that only its underbelly is visible, but a quick internet search reveals important clues.

For some reason, many are inclined to exaggerate the size and associated danger of our native snakes. The provided article, and the embedded quotations, are no exception. I suspect they only encourage others to kill snakes because they fear their safety and well-being are in jeopardy, when nothing could be further from the truth.

A large Gray Rat Snake captured in southwestern Georgia

Update: The newspaper in question has published a correction to their story. Within this correction, a Delaware biologist identifies the snake as a rat snake. But then, states that only experts can identify snakes. Do you think this is true, considering the initial reaction of the 13-year old who first spotted the animal?

Monday, September 21, 2009

Dead Coosa County Timber Rattlesnakes

In the last week or so, a few colleagues and readers have brought to my attention a recently circulating e-mail that purports to tell the story of a number of Timber Rattlesnakes found under and around a hunting club cabin in Coosa County, Alabama. All the snakes were killed, including three adults and over thirty juveniles. It's been a big snake year for Coosa County, already a coral snake has been found there after being undetected for forty years and I recently heard of a pigmy rattlesnake that was found dead on the road (often a useful means of finding rare snakes).

From the e-mail I received:

"Went to our hunting club in Rockford , AL for clean up day and here are some pics of what we found. These pictures are of what came from under the front steps of the club house!...I have heard of two tales in my life of people encountering a hoard of snakes like this but I have never seen anything like this! One of the members was weed-eating around the steps when the first large one came out. He got his gun and shot it. Then another guy killed another one of the 3 big ones. Then some of the little ones started coming out. Killed the rest with a hoe. Finally poured some gas around the steps and ran the rest of them out and you can see in the pictures how many were wound up killed..."

I have edited out some information in the e-mail pertaining to the names and addresses of those involved. And I'll give the hunters the benefit of the doubt and suggest that they killed the snakes because they feared for their safety.

One of the reasons I was forwarded this e-mail was because two of my recent posts (here and here) described some commonly circulated pictures of dead snakes with grossly exaggerated stories or descriptions. However, there is nothing within this story or series of pictures that suggests to me that this did not occur exactly how it was described.

Timber Rattlesnakes are known from this region of Alabama and that the incident occurred on a hunting club suggests there were a lot of woodlands in the area; good snake habitat.

Timbers also like to hide under structures (often rock piles), which made the crevices and hide-outs under a rarely-used hunting cabin an excellent place for the adults to take up residence. At least, it seemed like an excellent place at the time.

The size of the dead juvenile snakes suggested that they were newborns and this is the time of year (i.e. the fall) that rattlesnakes will give birth. Thirty four (give or take) babies is a lot for one snake (23 is the most I've heard of for a Timber), so I think it's likely that these babies are from more than one snake. Perhaps two or three of the adults in the pictures were the mothers.

Again, it's hard to fault people for destroying rattlesnakes on their property when they fear for their safety, but killing them was probably their most dangerous course of action as it greatly increased their chance of a bite. Perhaps the snakes would've dispersed into the surrounding woods by the time hunting season rolled around. Perhaps nobody would've ever known all those babies were there if the first adult snake hadn't been spotted. We'll never know.

In the future I hope they maintain their cabin and the surrounding area in a fashion that discourages the reptiles from taking up residence in the first place (i.e. removing brush and hiding places).

Just think of all the rats and mice that are now free to casually explore the hunting cabin...