A Serious Sipedon

Predation, or when one organism eats another, is common a phenomena at the dinner table. Out in the wild though, predation has a mythic quality to it: we know it happens, be we rarely get to see it. Fortunately, I witnessed such an event this past weekend.

While hiking on the boardwalk at a local marsh (as part of a birding competition no less), I couldn't overcome my habit to continually look at the ground. Out of the corner of my eye, I saw a rather perplexing shape. It had the scales and pattern of a snake, but it was big, round, and short. It took me a second to realize that I was looking directly down onto a water snake in the middle of eating a frog.

Upon closer inspection, it was a Northern water snake (Nerodia sipedon "serpent flowing through causing decay", Greek) eating a green frog (Lithobates clamitans "yelling one who haunts a stone", Greek; maybe this predated individual should be re-classified as Lithobates calamitati "misfortunate one who haunts a stone"--etymology joke!). Northern water snakes are active hunters, and they can use both olfactory and visual cues to hunt for prey. They are solid swimmers with physiological adaptations for increased blood oxygen capacity. As a result they can stay submerged in water for over an hour (65 minutes).

The water snake slowly swallows the green frog. The frog is so large,

the snake must unhinge its jaws to swallow the frog whole. Coming back

30 minutes later, you can see the frog is now midway down the snake's body

(bulge near the stick in picture four).

The diet of Norther water snakes is mainly comprised of fish (50-96% of diet by volume, 56-90% of diet by frequency). Most species consumed are rough fish (a term simply meaning that anglers don't care too much for them as sport), and many are consumed as carrion. Amphibians make up the rest of their diet, but they are often eaten less frequently (4-52% of diet by volume, 17% of diet by frequency). Nevertheless, Northern water snakes are a generalist, and they have also been documented to eat shrews, crayfish, leeches, and a whole host of other animals. In the case of our misfortunate green frog above, we don't know where the green frog was actually caught. Northern water snakes can hunt on the water's surface or swim underwater to hunt. As the case is here, prey are usually brought to a shallow area of water to work about in the mouth.

Unfortunately, Nerodia water snakes of all kinds are often confused with cottonmouths (Agkistrodon piscivorus) an aquatic venomous viper. Nerodia actually have no venom, and their first instinct is to escape by swimming or diving. Otherwise, when harassed, they have a vile temper. Just think, it's probably because they could be fishing instead of dealing with you!

References
All facts come from the Nerodia sipedon species account found in:
Ernst, CH & EM Ernst. 2003. Snakes of the United States and Canada. Smithsonian Books.

On the Road Again

(Disclaimer, if you don't like animal guts, skip this post).

Also, double post this weekend, so don't miss “Quoth the Marsh”

Most normal people would not consider any road kill all that special, particularly if it is a snake. Even though I am human, I most likely wouldn't fit the bill for being normal. Naturally, when I saw a Eastern Common Garter Snake (Thamnophis sirtalis sirtalis) dead on the road, I had to pull over and snag it.

 The specimen in question. Depending on the subspecies,

it can take two the three years before females can reach reproductive maturity

Now, even further from being normal, I decided to dissect the snake so that I could try and get a whole snake skeleton to put together as a model. It was also a unique opportunity because she was gravid, and you could feel the embryos in her gut.

Common Garters are not having too hard of a time compared to most snakes, but it is still sad to see a gravid female killed by a car. There were a total of five embryos inside her. Garters are ovoviviparous, meaning that they produce offspring within an amniotic sac and give live birth. It takes 80 to 90 days for gestation to occur (depending on environmental temperature), and a female can birth between 1 and 101 offspring depending on size and maturity. Females will only breed bi-annually or tri-annually. 

One of five embryos inside the snake. It's rare to get to see offspring

mid-development. The top picture shows the developing snake inside its own membrane.

The second shows it outside of the membrane.

Interestingly, the Common Garter snake is the northernmost snake species in North America. This is because it can tolerate a wide range of temperatures and can even survive being frozen for brief periods of time. Found in a variety of different habitats, the snake is most commonly found near wet areas. As there are many subspecies of this snake, coloration, diet, and behavior can vary drastically.

The Common Garter Snake is also the most deeply studied snake in North America.

For more info, see Snakes of the United States and Canada by Ernst and Ernst

Snake, Rattle, and Roll

These past couple of weeks have been fairly busy (and it wasn’t the Avengers movie this time, although Men in Black 3 was entertaining); instead, I have recently returned from an adventure to the northern Midwest. Shortly upon returning home, I packed everything and moved up to New Jersey. I will be in the Garden State for the summer, working at Wallkill River National Wildlife Refuge.

While on my adventure, I had the pleasure of exploring some great prairie bluffs with a variety of folks. Without them, my trip would have not been nearly as fascinating or rewarding.

We looked a few different places for the snakes, and it looking through brush and under shelf-rocks.

Venomous snakes should never  be handled with bare hands, so snake hooks were used hold them and

release them.

Perhaps my favorite one of my favorite experience was finding my first wild rattlesnake. In this case it was the timber rattlesnake (Crotalus horridus “The horrid rattle tail”). Like many of the world’s critters, these snakes are declining across their range in the Midwest, South, and Northeast. Besides its loss of habitat, snakes receive a fair amount of persecution.

 

 The famous rattle of the rattlesnake. This individual had a surprisingly large rattle,

as they can often break.

The timber rattlesnake, which can grow up to almost 6 feet, has been exterminated by shotgun, by car (snakes are an easy target on the road), and by yearly roundups in some locales (killings of almost entire snake populations). Historically the snake was considered for our national animal (think “Don’t Tread On Me”), and Benjamin Franklin considered the timber rattlesnake to be of higher character than the bald eagle.

Timbers are relatively rare, are secretive, and are mild-mannered compared to other vipers (like many other venomous snakes, timbers have infrared sensing “pits” nears their eyes and nostrils”). They like south-facing woodlands, montane regions, rock shelf, pine savanna, and swamps.

A brief video of one of our encounters. This dude suprised us while he was basking,

and then he headed straight for his home under the boulder.

While timbers are often killed because of the fear they impose, they rarely bite humans unless greatly provoked. Sometimes they will strike defensively with a closed mouth. Mostly, timbers use their potent venom to hunt small mammals—namely mice (38%) and chipmunks/squirrels (25%). Interestingly, timbers only eat 6-20 meals annually, and over a year, they eat twice their body weight mass. I have to say, I would love my grocery bill if I could eat that little. Unfortunately, I will never have the metabolism of an ectotherm.


All facts were from publications found in Snakes of the United States and Canada authored by Ernst and Ernst.