Monday, November 11, 2013

Taking Note: I Finally Found the Snake that Feigns Death

    The skies were blue, the water was beige, and the sun was basically white on a September Monday in Macon County, Alabama. Turkey Vultures soared above and Cricket Frogs skipped below as I made my way down a dried-up dirt road, heading down to the river. I was leading the Auburn University Vertebrate Biodiversity class to catch stream fishes, and I was mighty content.

    On our way down to the creek, the students and I did our best to bring most* any vertebrates to hand. I quickly grabbed a Banjo Frog (Lithobates clamitans), rattled off its Latin name, and showed the students diagnostic characteristics to identify the species. Shortly thereafter, I dove head first into a thicket after a Six-lined Racerunner (Aspidoscelis sexlineata), but, true to its name, the lizard raced off uncaptured. All the while, the students dutifully jotted notes into their field notebooks, recording the names, characteristics, and various other details about the vertebrates we observed. 

    The field notebook is an important part of this course. In addition to teaching the identification and ecology of vertebrates, we also attempt to instill practices of good field biologists, which includes the mechanics of quality field notes. Students are required to carry a field notebook on their person during field trips, and they are graded by the quality of the notes taken. Good field notes typically involve the Who, What, Where, When, Why, and How: the people present, animals observed, locality, date, purpose of the trip, and methods employed to observe animals. 

    The reasons for taking detailed field notes are many, and I won’t belabor them here. However, I think the most simple and obvious justification is that, no matter how good of a memory a person may have, memories from the field will ultimately be forgotten. I mean, I can’t remember what I had for lunch yesterday, and my Dad can’t remember the names of his own children, so between the two of us, we definitely can’t remember which wildlife we observed while hiking “in the Cuyahoga Valley National Park that one spring day in 2009”. But with an oft-used field notebook, the field notebook provides a written record of activity for when memory inevitably fails.

    And after my failed capture of the racerunner, I clumsily lifted myself up, and our group continued on. The sandy shores of the river were in sight, and the rattling call of a Belted Kingfisher serenaded our ears…..until my ears were pierced by the screams of students. I turned back and quickly saw the source of the commotion: a snake, black as night but clear as day, stretched alongside the path. A snake which I had walked right past without noticing. (Whoops!) 

    My jaw dropped. It couldn’t be. But…no…yes, it was. My gear fell to the ground, and I started jumping with joy. This was no common Black Racer, not a Grey Ratsnake, nor was it a Cottonmouth. This was a serpent that had been eluding me, well…my entire life: I had never seen one before. The black snake coolly stretched in our midst was an Eastern Hog-nosed Snake (Heterodon platyrhinos).

    I excitedly gathered the students around and started to tell them about the fascinating creature. Heterodon platyrhinos has a wide distribution throughout eastern North America, ranging from Canada south to Florida, Texas, and everywhere in between. Not surprisingly, the common name ‘Hog-nosed Snake’ is attributed to the enlarged and upturned rostral scale on the snout, which, for a snake, somewhat resembles a pig’s nose in both form and function. The snout is used to dig through sand in search of the species favorite prey, toads (Anaxyrus species). Because color pattern is variable for this species the upturned snout is the key diagnostic characteristic to identify this species.

    I explained to the students that this species is well-known for its hilarious behavior when being harassed by potential predators. As an example, I gently grabbed the snake’s body, and the show began. First, it fanned out its neck and winded its body drunkenly through the air, hissing slightly with mouth agape. Because I wasn’t deterred by the cobra-like bluff, the snake then shot a partially digested toad out of its mouth and pooped all over itself. Finally, with the air ripe with snake musk and laughter, the snake rolled over and proceeded to fake its own dead. We flipped it over right-side up a few times, but the snake consistently rolled back over, ‘dead’. 

    Despite some initial apprehension, the students ultimately enjoyed the snake as much as I did. After a few pictures and a great educational experience, we placed the Eastern Hog-nosed Snake back where we found it, and continued on to catch and identify stream fishes. We observed a few Rock Darters (Etheostoma rupestre), Stonerollers (Campostoma oligolepis), Blacktailed Shiners (Cyprinella venusta), and Skygazer Shiners (Notropis uranoscopus). But on our return to campus, the students mostly agreed that the find of the day was the Heterodon.

    I have been out hiking around eastern North America in search of snakes for a couple years now, and this species eluded me until now. Given my experiences, I consider this species to be fairly rare. The classification of species as ‘common’ or ‘rare’ has a long history in studies of natural history, ecology, and conservation biology. By describing species as existing at one end or the other on the spectrum of commonness to rarity, one is able to convey basic but considerable information about the distribution and abundance of those organisms. However, in reality, the concept of rarity is more complex than a black-and-white scale may indicate. 

    Rabinowitz (1981) created a classification scheme diagnosing different forms of rarity based on three factors: geographic range, habitat specificity, and local population size. Under this scheme, species can be considered rare if they are deemed low for at least one of the variables, such as a limited geographic range, narrow habitat specificity, or low local population size. 

     When considering the seven forms of rarity, H. platyrhinos has a wide geographic distribution and is not rare in that regard. However, this species probably occurs in lower population densities than others: there are simply fewer Eastern Hog-nosed Snakes out there than Black Racers, so the former is less commonly seen. This species also is somewhat of a habitat specialist, preferring xeric sandy habitats. A final aspect lending to rarity may be that this species’ unique natural history strategies (e.g., fossoriality) may render it more ‘rare’. 

    While I can’t be sure why it took me so long to find an Eastern Hog-nosed Snake, it seems like I’ve seen hundreds, maybe a thousand of other snakes in recent years. Which got me thinking: how many snakes did I see before finding an Eastern Hog-nosed? I don’t know off the top of my head, but if somebody dusted off my field notebooks, we could find out.

*Except venomous snakes.

Other Readings:

Grinell, J. (1912). An afternoon’s field notes Condor, 14, 104-107 DOI: 10.2307/1362226

Rabinowitz, D. 1981. Seven Forms of Rarity. Pp. 205-217 in Synge, H. The Biological Aspects of Rare Plant Conservation. John Wiley and Sons.

Steen, D. A. (2010). Snakes in the grass: Secretive natural histories defy both conventional and progressive statistics Herpetological Conservation and Biology, 5, 183-188

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