Thirteen winning essays from the YNA 2002 contest year
When you think of New York City, you probably form a vision of its brilliant architecture and marvelous skyline. Many tourists are attracted to this beautiful city from all over the world every year for this very reason. New York is known as the city that never sleeps, with lots of commotion all day and all night long.
When you think of New York City, however, herpetology is probably not the first word that comes to mind. Most people are not aware that this city provides a habitat to many different species of turtles. In fact, turtles live in natural areas located throughout the five boroughs. Manhattan‘s own Central Park is home to a diverse ecosystem that includes a variety of turtles.
In this study, I will investigate turtles' basking behavior. I chose this topic because when I was nine years old, I received my first red-eared slider as a pet. My elder brother gave it to me. This slow-moving animal, with its unique carapace, has made me curious about turtles ever since. As a curious nine-year-old, I noticed that my turtle often remained in a stationary position; I never knew the purpose of this behavior. This wonder still remains and has developed into a deeper form of curiosity.
People may be familiar with turtles from reading folktales and watching cartoons, but these reptiles are biologically unfamiliar to most (Zipko, 1982). Turtles are fascinating animals. They have the ability to regulate their body temperature through both behavioral and physiological adaptations (Hutchison, 1979). For example, in order for a turtle to obtain body heat, it must be able to use the energy radiated from the sun. This phenomenon, known as basking, has generally been assumed to be for thermoregulation. Thermoregulation is necessary in order to maintain a balanced body temperature in reptiles (Zipko, 1982).
My expedition takes place in Turtle Pond, located in Central Park in New York City. This pond was artificially made, though it features all the characteristics of an actual natural pond. This area is part of Central Park‘s "quiet zone," with strict regulations regarding noise pollution. Any action that could disturb this peaceful area is prohibited, such as musical instruments, swimming, fishing, and running.
Expedition #1: October 26, 2001
As I began heading toward Turtle Pond, my heart was filled with excitement as I directed my thoughts toward the turtles, hoping to find them at this time of the year. It was a very unusual day for turtle watching because the temperature had dropped to 11° Celsius. I could feel the chilly wind blowing in my direction and the cold piercing my face. As I looked up into the sky, I observed the sun and the clouds above me. I began wishing for a much warmer day. When I finally arrived at Turtle Pond, the first thing I noticed was Belvedere Castle. It is a four-story medieval-style structure that is used for field observations and sightseeing.
I quickly ran up the steps of the castle, and when I arrived at the top, I stopped to take a breath and recorded my arrival time: 10:45 am. I walked toward the edge of the tower and looked down at Turtle Pond. Rocks and grass surrounded the pond. To the east of the pond is a small marsh, with a three–foot–long log jutting out toward the pond. I lifted my binoculars and focused the lenses until it was clear enough to search for turtles. After several minutes, I finally spotted some turtles basking on the rocks near the pond, as well as one turtle basking on the log. I recorded my observations in my field journal.
The turtles were basking on three different rocks. I decided to label these rocks according to their distance from me: Rock No. 1 was 50 meters from my perch, Rock No. 2 was 45 meters away, and Rock No. 3 was just 25 meters away. I then took some photographs of the turtles and the scenery.
I carefully examined the turtles‘ positions. Several turtles were piling on top of one another. Most of the turtles‘ arms, legs, tails, and necks were stretched out to the extreme. All the turtles lay motionless on the rocks. Because their shells appeared to be dry, I figured that they must have been basking for a long period of time before I arrived. I remembered seeing a picture of the same species of turtle once before. They matched the characteristics (http://www.animaldiversity.ummz.edu, site information retrieved October 26, 2001) of the eastern painted turtle (Chrysemys picta).
Before discussing the remainder of my expedition, I believe it is important to provide some background information about the general characteristics of eastern painted turtles and how they were introduced to Central Park. Eastern painted turtles have yellow–and–red shell patterns. The edges of their shells are covered with red designs. The females usually grow larger than the males; however, the males have longer foreclaws and tails (Conant & Collins, 1998). Eastern painted turtles are native to this area. (According to a sign I read in Belvedere Castle, the ancestors of these turtles were most likely discarded near the pond by people who no longer wanted them as pets.) Eastern painted turtles now compete for survival among native animals, in particular the red–eared slider (Trachemys scripta). The eastern painted turtle population, consequently, is jeopardized by the non–native the red–eared slider.
I used my thermometer to measure the air temperature. It read 12° Celsius. I then measured the water temperature. It read 10° Celsius. Afterwards, I returned to the castle and found that the turtles had remained in the same position. I continued to observe the turtles for any signs of movement, but they just sat there basking, motionless. I watched the turtles throughout the morning. At 1:05 pm, a turtle swam past Rock No. 3 and stared at the rock for 20 seconds, then turned back and swam away.
It seemed that this particular turtle may have wanted to bask on Rock No. 3, but there were six other turtles already occupying the rock. This made me wonder: why would all the turtles choose to bask at only three particular sites and pile on top of each other, especially when there were many other sites available? Why didn‘t the turtles choose other nearby rocks that were not so crowded?
Next, I analyzed each of the three sites. I realized they had two important common factors: safety and the greatest intensity of sunlight. The rocks and logs were located in an area away from human reach. It was quite difficult for me to get close enough to the sites to take a clear picture of the turtles basking, even with a zoom lens. These sites, located in the prohibited areas, were situated in areas of intense sunshine.
By 2:06 pm, there were not any turtles basking on Rock No. 1 and Rock No. 2. Rock No. 3 had three turtles remaining. This event surprised me. What could have caused all of these turtles to stop basking and jump into the water within seconds of each other? I recalled some of the field observation techniques that my teachers and friends advised: "Carefully observe and record everything that happens. Look around for any predator or human disturbance that may affect the turtles‘ basking behavior." I tried to recapture the event: I did not notice any predators or any signs of human disturbance. As I still could not figure out why, I became frustrated; the temperature dropped, so I decided to conclude the day‘s field observations.
Expedition #2: October 27, 2001
It was 11:45 am and the temperature was 12° Celsius. The breeze blew across the pond, forming small ripples on the surface of the murky water. It was silent, except for the birds chirping and an occasional car in the distance. The leaves on the trees had begun to change into their autumn colors; some of the leaves had already fallen to the ground. The sky was cloudy. For a moment, the scenery made me feel as though I was no longer in Manhattan, but in the countryside, away from the commotion of the city.
I gazed at the pond for signs of turtles. As I looked through my binoculars, I instantly spotted turtles on the rocks. Although the image was distorted because of the great distance between the pond and me, I noticed two turtles were basking on Rock No. 1, seven turtles were on Rock No. 2, and two turtles were on Rock No. 3. Subsequently, I challenged myself to classify the various forms of turtles. I found it difficult because I am inexperienced and the turtles were far away from me. The previous night I researched information concerning the different characteristics of the various turtles that are found in Central Park (http://www.animaldiversity.ummz.edu, site information retrieved October 26, 2001): musk turtles (Sternotherus odoratus), snapping turtles (Chelydra serpentina), red-eared sliders (Trachemys scripta), and eastern painted turtles (Chrysemys picta).
I struggled to identify the turtles based on the information I had gathered and using taxonomic classification techniques. I tried to be accurate in classifying the turtles. The red-eared slider, for instance, has a red stripe behind the eyes, with a green carapace. The plastron, or ventral part of the shell, is composed of yellow designs with a series of somewhat elliptically shaped figures (Conant & Collins, 1998). Musk turtles, on the other hand, are commonly characterized by an oval shell, often in a lustrous brown or black hue. They are relatively small, ranging from three to five inches in length (http://www.animaldiversity.ummz.edu, site information retrieved October 26, 2001).
After a long period of careful observation, I identified the various types of turtles that were basking together. On Rock No. 1, one red-eared slider and one eastern painted turtle rested together. On Rock No. 2, I observed one red-eared slider and six eastern painted turtles. Finally, on Rock No. 3, there were two eastern painted turtles. I did not identify any musk turtles or snapping turtles.
During the previous expedition, I had failed to answer my question as to why the turtles had jumped into the water within seconds of each other. This time, I tried to be more aware of the turtles‘ environment. I also focused on several biological and behavioral factors: thermoregulation, safety, basking duration, and the intensity of light. Would any change in one or more of these factors impact the turtles‘ basking behavior? During the last expedition, there did not seem to be evidence of external threats, so I concluded that the turtles were not hiding from predators. After careful consideration, I developed the hypothesis that the reason for such behavior could be attributed to changes in the turtles‘ internal body temperatures.
At 11:47 am, a turtle swam to Rock No. 2, touched the rock with its forearm, then turned and swam away. At 11:50 am, the red-eared slider that was basking on Rock No. 2 slowly made its way toward the edge of the rock. The red-eared slider dove into the water and slowly swam away, and was soon no longer visible. Were these two events related? Did the first turtle want to bask there? When the first turtle touched the rock, did it realize the temperature on the rock was inadequate for basking? Is that why it swam away? On the other hand, perhaps the turtle wanted to bask but realized the rock was overpopulated. Yet when the slider on Rock No. 2 swam away, I was convinced the temperature on Rock No. 2 was inadequate. This was not enough information to draw a conclusion, as the remaining six turtles were still basking. Again I was frustrated. My expedition ended at 1:02 pm with no turtles basking on Rock No.1, four turtles basking on Rock No. 2, and none on Rock No. 3.
Expedition #3: November 10, 2001
It was 12:44 pm and the temperature was 9° Celsius. Only one turtle was basking on Rock No. 1, nine turtles were basking on Rock No. 2, and there were not any turtles basking on Rock No. 3. At 12:46 pm, one red-eared slider swam toward Rock No. 2, slowly climbed onto the rock, and stretched out beside the other turtles that were already basking. At 1 pm, the same red-eared slider climbed on top of another red-eared slider and continued basking in this position.
The turtles continued to bask on the rocks, motionless. By 1:25 pm, the temperature dropped to 7° Celcius. There were no other signs of turtles around, except for the ones already basking. Over the next 15 minutes, I realized that as the temperature dropped, the turtles began to fidget on the rocks. Many of the turtles dived into the pond.
By 1:42 pm, there were no longer any turtles basking on the rocks. I looked up at the sky and discovered the most important factor in my expedition—the position of the sun. The sun had shifted toward the west and therefore had cast a horizontal shadow upon the rocks. I believe that the sun‘s position influenced the duration of the turtles‘ basking. Since turtles‘ internal body temperatures are influenced by their external environment (Leuteritz & Manson, March 1996), I conclude that the shift in the sun‘s position decreased the intensity of light and triggered a behavioral response by the turtles.
After participating in both field expeditions and supplemental research, I have come to the conclusion that as the intensity of sunlight declines, so does the duration of the turtles‘ basking. Based on my observations, the turtles tended to bask in areas where they were not disturbed by human behavior. According to Leuteritz and Manson, human interference interrupts basking and thermoregulation, which aids in the digestion of food and therefore affects the health of the turtle population.
Participating in this study opened my eyes to the challenges faced by field biologists. I learned that conducting an expedition requires perseverance and thorough observation. I wanted to find the answers to my questions as soon as possible, but I soon realized that it takes a great deal of time and patience before confidently stating a conclusion. Throughout this study, I was filled with both anticipation and frustration. The most satisfying part of my expedition came when I started making connections based on the data compiled during my expeditions.
My study took place in an urban area in which it can be difficult to conduct expeditions. Deciding on a location for my research was extremely complicated due to the never–ending bustle of New York City. Transportation was also a challenge: in order to travel to Central Park from where I live, I had to take a 45–minute subway ride. These hurdles were well worth it, however: I learned what it takes to participate in field biology, and I was able to investigate an aspect of turtles‘ behavior that I had been curious about since I was very young.
"Chelydra serpentina." Retrieved from the World Wide Web on October 26, 2001: http://animaldiversity.ummz.umich.edu/accounts/chelydra/c._serpentina$narrative.html
Conant, Roger and Joseph T. Collins. Reptiles and Amphibians. New York: Houghton Mifflin Company, 1998.
Hutchison, Victor H. Thermoregulation. New York: John Wiley & Sons, 1979.
Leuteritz, Thomas E. and Cynthia J. Manson. "Preliminary Observations on the Effects of Human Perturbation on Basking Behavior in the Midland Painted Turtle (Chrysemys pictamarginata)." Bulletin of the Maryland Herpetological Society 32.1 (1996): 16–23.
Map of Central Park: My illustration was adapted from a map on the following site on the World Wide Web, retrieved on October 27, 2001: http://maps.yahoo.com
"Sternotherus odoratus." Retrieved from the World Wide Web on October 26, 2001: http://www.animaldiversty.ummz.umich.edu/accounts/sternotherus/s._odoratus$narrative.html
Temperature Chart: Adapted from the following site on the World Wide Web, retrieved on October 27, 2001: http://www.weather.com/weather/local/10022
Zipko, Stephen J. "Basking Behavior of Painted Turtles." The American Biology Teacher, 43.8 (1982): 406–412.
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