Monday, May 11, 2009

Size Doesn't Matter

As the end of the semester is right around the corner, most students likely spent their Friday night tying one on at the bar. I on the other hand, was more concerned with tying my shoes on, tightly, so they wouldn’t get sucked off my feet as walked through the muck on the bottom of a farm pond.

We were back in Henry County, Alabama, for another attempt to gather some greater sirens for a study back in Auburn. The goal was to arrive after dark to seine, trap, or otherwise get our hands on one of the slippery, slimy amphibians. Once captured, the animals would be safely transported back to campus and held in aquariums to take place in a respiration study. The research aims to determine how sirens best absorb oxygen through the water. It’s always difficult to conduct a study on animals other than lab mice, because you can never count on having an easy time finding your subjects. This is particularly true when they live in the weeds and mud of swamp bottoms.

After we exited the van and prepared to enter the pond, a sharp exhalation of breath caught my attention. I slowly turned around and illuminated about two dozen cows with my headlamp. Their eyes glowed white as they staring inquisitively at me. So as to not alarm the giant, lumbering animals, I quietly turned around and crept into the water. I hoped the curious beasts would choose not to investigate beyond giving me more unsettling looks.

For the first time this year, I could hear barking tree frogs (below) calling.


Off in the distance, there was a full chorus of this species singing to one another. We consider these congregations a full chorus when there are so many calling frogs that we cannot distinguish individuals, just a lot of singing frogs. Periodically, one of a few bullfrogs would catch our attention with their long, deep, resonating bellow. There were also green tree frogs, bird-voiced tree frogs, and cricket frogs calling. Not a bad complement of species for a pond in the middle of a cow pasture.

My ankles submerged in the water, I waited a few seconds and let the mud seep through my sneakers. I always find it necessary to adjust to walking through the mud. There’s something that feels inherently wrong about striding right into swamp muck when you were sitting in a van listening to music and minding your own business just minutes before.

As I stood in the water I took in the swamp. In contrast to my visit in March, I could see several pairs of orange eyes looking back at me, illuminated in the beam of my headlamp. As the weather warmed in the last few weeks, the alligators emerged. There were a couple alligators zooming around the main pool of the swamp, perhaps hot on the trail of prey. I could also see the eyes of a smaller, solitary and motionless alligator about 20 feet away. Instinctively, I scanned the water around my legs and watched my step, although I knew there was unlikely to be any danger.

Alligator eyes, and those of the curious cows, reflect light because of a layer of tissue in the back of their eyes called the tapetum lucidum (which would be an awesome band name). The tapetum lucidum reflects available light onto an animal’s retina. This allows the animal to see better in the dark by making the most of the little light that’s available. As you might expect, tapetum lucidums are most often found in nocturnal animals. One side-effect of this tissue is bright and glowing eyes when illuminated by a flashlight. It’s a lifesaver too; the bright eyeshine of a deer in the road has likely averted many car accidents.

Putting the cruising alligators out of mind, I began to help seine through the waters of the swamp. Sirens spend most of their time within dense aquatic vegetation or within packs of leaves that settle at the bottom. In these hidden areas, they wait to ambush prey, such as small fish or tadpoles. They’re also safer here from predators, like the patrolling alligators. There wasn’t a lot of cover in this pond, however, and we struggled to find areas that looked promising.

By the time 11:00 had rolled around, we had yet to match the total catch of our previous attempt, a single siren. We were, however, hauling in plenty of small bluegill, largemouth bass, and crayfish. We held a few of the latter to feed the captive siren at Auburn. It was apparently a picky eater, and would only accept the clawed crustaceans. Resigned and tired, we decided to give the seine one last try.

As we hauled the net out of the water, we noticed a larger than usual mass of weeds. It was a promising pile that we set upon with an enthusiasm that defied the late hour. A brown squiggling form caught our attention, but it was revealed to be a small bullhead, a type of catfish. It was carefully grabbed and thrown unceremoniously back into the swamp. Following the catfish were numerous dragonfly larvae, more bluegill, but no giant writhing form that would give away the two-foot long amphibians we were after. Resigned, we started to toss back the clumps of vegetation into the water, just in case there was a fish stuck inside that we missed, and rolled up the seine in preparation for the drive home. When the last clump of swamp weeds was removed, a slight movement caught my eye.

A tiny, eel-like animal wriggled within a slight puddle in the mud. It was with great excitement that I scooped up the beast and exclaimed that the expedition was a success after all; we had captured a siren barely an inch long. It was a larval siren. When greater sirens are babies, they’re miniscule and incredibly difficult to find or trap. In fact, it was the first one ever recorded from the state of Alabama.

1 comment:

MB said...

"...a layer of tissue in the back of their eyes called the tapetum lucidum (which would be an awesome band name)."

Dang, boy, you're alright. A fan of Dave Barry's is a fan of mine (or whatever). And congrats on a successful outing at Hutto Pond!