Birds as Indicators of Water Quality on Mac's Pond

Transcription

1 Birds as Indicators of Water Quality on Mac's Pond Stephanie Zanati Natural History and Ecology Investigation Project February 16th, 2012 Abstract This paper seeks to elaborate on an investigation I conducted in Mac's Pond. Islandwood's Mac's Pond is an interesting place: A shallow, fishless, man-made pond. Without the presence of fish, I turned to birds as indicators of health, collecting data on bird species and behavior, as well as water quality data. I synthesized this data with background research on the history of Mac's Pond, other general indicators of pond health, as well as the diet and habitat requirements of birds observed during my investigation. The diversity of bird species observed suggests an abundance and diversity of food availability, such as macroinvertebrates and aquatic plants. This leads me to conclude that the diversity of birds are an indicator of the health of Mac's Pond, because it is able to support a wide variety of life forms. Zanati, 1

2 Arriving in the Pacific Northwest for the first time this past August, most everything here was foreign to me. I thought Mac's Pond would be one of the only ecosystems I encountered with some semblance of familiarity. And I was wrong! I remember the day when Christina Doherty shared with me that there are no fish in Mac's Pond. I found the thought of this incredibly fascinating; who ever heard of a fishless pond? I certainly had not until arriving here. My own conception of a pond ecosystem was totally disrupted. This had me thinking about how differently this pond must function from any other pond I'd ever observed in my life. It seemed to me impossible that this pond could function in my own conception of "normal". An important indicator of health in a pond I have always relied on has been in a pond's ability to support fish life. In Mac's Pond we don't have to worry about that. Without fish, birds take the spotlight as the highest trophic level in Mac's Pond: the most visible and obvious indicators of the pond's ability to thrive. So then, the idea for my Natural History and Ecology project was born: In the absence of fish, what do the birds tell us about the health of Mac's Pond? It seems appropriate to begin my pond investigation by defining a pond. A pond is a body of water that is generally shallow enough to support plant life around the shoreline, from shore to shore, in its muddy or silty bottom. (Cavuto, 1985). This profusion of plants lends itself to birds that seek shade and security, for breeding or nesting. Food is also plentiful along its shallower edges. (Benyus, 1989). Mac's Pond surely fits this description. But while a pond exists within distinct ecological boundaries, Mac's Pond has an interesting and unique history: The stream that became the pond was once dammed to use as a water reservoir in the late 1800's for use by Blakely Mill workers and Blakely Harbor residents. After the mill closed, it then becoming a swimming hole for locals. In 2001, the pond was upgraded to provide safe access points for use by students visiting the property, becoming private property, having already been purchased to become the Puget Sound Environmental Learning Center, which is now Islandwood. As part of the plans of the upgrade, the pond was drained and all fish were Zanati, 2

3 removed. (Daley, 2001; Anderson 2011) So, a pond it may exist under a wide variety of conditions and sustaining many different types of life. No two ponds are quite alike, and do not require fish to fit its definition. According to the Encyclopedia of Inland Waters, typical ponds are even likely to be more productive than lakes, owing to the greater recycling of nutrients that become available to phytoplankton and other aquatic plants, as well as receiving higher nutrient input from the cultivated landscapes they are often found in. In fact, the lack of fish which sometimes occurs in shallow, isolated bodies of water (such as Mac's Pond) may actually lend itself to the pond's ability to have higher species richness than their deeper cousins, the lakes. Unlike a lake, in which inhabitants have lower colonization opportunities due to stronger changes in water depth, a shallow pond can have more abundance in waterfowl, invertebrates, amphibians and plants. (Meerhoff & Jeppesen, 2009). However, an abundance in waterfowl may not necessarily be a good thing in a pond. A study in England conducted on the impact of waterfowl on a fishless, shallow pond in England concluded that waterfowl can have detrimental impacts to a pond ecosystem, especially in wintertime when aquatic plants serve as a main source of food. Over-grazing and trampling damage can prevent aquatic plants from re-establishing their populations in the spring time, leading to low turbidity and dangerously high nutrient levels. (Chaichana, Leah, & Moss, 2011). However, another study I read stated that shallow lakes and ponds can maintain alternative equilibria not typically associated with health and stability. A pond can be clear and dominated by aquatic vegetation, or it can be very turbid with high algal biomass. This possibility is promising, from a management point of view, because it suggests that disturbed ponds can remain stable despite high levels of nutrients. I also gathered additional information from Matt Schmidt, the accomplished and highly knowledgeable ornithologist in Islandwood's kitchen. Over the last several years, there have been Zanati, 3

4 incredible bird sightings at Mac's Pond. He has personally seen a number of quite aberrant species in his time here, including sandhill cranes, trumpeter swans, and once, a hawk owl (Schmidt, 2012). This information had me hopeful that there would be high levels of bird diversity in Mac's Pond. My method of gathering data during the groundtruthing process was fairly simple and straightforward. Over the course of seven days, I visited Mac's Pond to collect data. The data that I collected consisted of the time of day, a weather observation, air temperature, water temperature, dissolved oxygen level, and observation of bird species. In my observation of bird species, I took note of the numbers and sex of each species, along with their behavior and location in and/or around the pond. I began on February 2nd, 2012 at 11:23 AM. It was cloudy, 6.8 degrees Celsius. The water temperature was a mere one tenth of a degree less than the air temperature. The dissolved oxygen was 6.8 mg/l. I observed 2 male buffleheads diving, 3 ring-neck ducks, two males and one female, and one male mallard. The next day, on February 3rd at 8:15 AM it was 6.7 degrees Celsius, sunny and calm. The water temperature was 5.2 degrees Celsius and the dissolved oxygen was 6.8 mg/l. I observed 3 buffleheads, two males and one female, they were not diving, just swimming in the center of the pond. I also observed two male red-winged blackbirds singing while perched in the cattails on the far side of the pond. At 8:30, the buffleheads dove under and re-emerged on the North side of the pond. And then, a river otter appeared! It swam from west to east across the pond, diving occasionally. It swam over to the stairs under the pond shelter, and presumably exited the water. This was exciting, although not pertinent to my research. I returned the same, sunny, clear day at 12:30 PM. The air temperature had increased to 11.5 degrees Celsius and the dissolved oxygen also rose to 8.4 mg/l. What was interesting was that the temperature of the water actually fell to 4.5 degrees Celsius. I saw (presumably the same) three buffleheads, three American wigeons, two males and one female, as well as a bald eagle which Zanati, 4

5 flew over the pond and perched in a Western Hemlock tree on the west side of the pond. What was a bald eagle doing at Mac's Pond?! Surely not fishing. I did not have a chance to go to the pond on February 4th, but I did return at 8AM on February 5th. There was about a 20% cloud cover on this morning, the air temperature 7.5 degrees Celsius, and the water temperature was 3 degrees Celsius. Dissolved oxygen was 6.4 mg/l. I observed three male red-winged blackbirds singing while perched in the cattails, a pair of buffleheads diving in the North part of the pond, and a pair of ring-neck ducks. Later on that day at 4PM, I returned. It was overcast with a light breeze. The air temperature was 11 degrees Celsius and the water temperature was 6.8 degrees Celsius The dissolved oxygen was only 2 mg/l! Despite the low level of oxygen in the water, I observed six mallards, three buffleheads, and a pair of ring-neck ducks. They were all congregating on the far North side of the pond, near the cattails. I also saw three red-winged blackbirds swooping in and out of the cattails and singing. The next day, February 6th, I went to the pond at 12:30PM. It was clear and sunny with a westerly wind that was strong enough to sway the branches in the trees surrounding the pond. The air temperature was 11.8 degrees Celsius, the water temperature was 7 degrees Celsius, and the dissolved oxygen was 6.8 mg/l. I observed two male buffleheads diving, a pair of mallards on the far northern edge of the pond eating and dabbling. I also observed three ring-neck ducks, one male and two females, preening and bathing. On February 7th, I went to the pond at 3:45 PM. It was partly cloudy and the air temperature was 10.2 degrees Celsius. The temperature of the water was 6.8 degrees Celsius and the dissolved oxygen was 6.2 mg/l. I heard what I could distinguish as three distinct red-winged blackbirds singing, as well as 2 pair of ring-neck ducks and a pair of buffleheads in front of the cattails diving. In the center of the pond were three mallards, one male and two females, swimming. In the far edge of the ponds, east of the cattails were a pair of American wigeons. Zanati, 5

6 My last day of observation was February 8th. I visited the pond at 8:30 AM on this day. The air temperature was 6.3 degrees Celsius, the water was 6 degrees Celsius, and the dissolved oxygen was 5.5 mg/l. I observed a pair of ring-neck ducks, a pair of mallards, and four red-winged blackbirds. In my observations, I noticed a few patterns. Firstly, the vast majority of birds congregated on the far north side of the pond, the opposite side of the Floating Classroom and stairs. This may be because this area tends to not have people in it, or because that side of the pond is seemingly less disturbed (i.e., no dam or accesibility to throngs of children). But more likely, it is due to the presence of a wetland on that side of the pond, which likely provides more food and protection than the south side of the pond. Another pattern I noticed was that the different bird species tended to stick to themselves and not intermingle between species. The last pattern that I noticed over the course of my observation was that I never heard any of the waterfowl I observed make any vocalizations, although I do admit that this may be because I was too far away to hear them, so therefore I cannot say for sure whether or not they did or did not during my periods of observation. Next, I gathered information about the habitat requirements and diet of the bird species I observed. The Bufflehead (Bucephala albeola) is a diving duck that is found in lakes, ponds, bays, and large streams. It breeds north of the US but winters in the Pacific Northwest. Its chief food items are insects, particularly dragonfly and damselfly nymphs, larval and adult beetles, and water boatmen. Buffleheads also eat crustaceans and mollusks. While they eat mostly animals, they do supplement their diet with weeds and grasses too. (Martin, Zim & Nelson, 1951). The Ring-neck Duck (Aythya collaris)is a common winter resident in the Puget Sound region. Unlike other diving ducks, the Ring-neck can take off directly from the water into flight. It tends to dive and dabble in fairly shallow waters. (Morse, Aversa, & Opperman, 2003). Its diet also includes both plants and insects, chiefly dragonfly and damselfly nymphs, but also midge larvae and mollusks, particularly univalves. Animals account for only about one quarter of their diet, and the rest is plants. Zanati, 6

7 (Martin, Zim & Nelson, 1951). The Common Mallard (Anas platyrynchos) very well may be the most abundant duck in the Northern Hemisphere. They can be found in virtually any fresh water where there is aquatic vegetation, although they are less common in mountains. They forage primarily in water; seeds, roots and leaves make up the bulk of their diet. Breeding females tend to favor insects. (Lichen, 2001). The Red-winged Blackbird (Agelaius phoeniceus) nests in marshes, meadows, or brushy edge habitats. They fiercely defend their territory with a variety of calls. They forage primarily on the ground for insects and seeds. (Martin, Zim & Nelson, 1951). The habitat of American Wigeon (Anas americana) include ponds, marshes, estuaries, and short grass fields. Their diet is primarily plant material, and they tend to graze more than other ducks. (Morse, Aversa & Opperman, 2003). The most charismatic bird I observed during my groundtruthing process was the Bald Eagle (Haliaeetus leucocephalus) but also seemed to be the most confounding. Prior to my research, I was under the impression that all Bald Eagles ate were fish. However, according to Birds of Seattle and the Puget Sound, Bald Eagles in the Northwest eat not only fish (primarily salmon), but are also quite accomplished scavengers and are also known to eat waterfowl. (Fisher, 1996). This explains what the bald eagle was doing at Mac's Pond, in the absence of fish. Their habitats are, generally speaking, near bodies of water. Based on my research and data, I am led to the conclusion that Mac's Pond, despite its fishlessness, still maintains a diversity and abundance of food sources for birds. This diversity suggests that Mac's Pond is a healthy pond. I am still, however, confounded by the wide range of temperatures and levels of dissolved oxygen and I am still curious if the time of day, temperature, or dissolved oxygen had any influence on the abundance of bird species at the time of my observation. The following graphs serve as leads to possible answers to these questions. Zanati, 7

8 07:12:00 PM 04:48:00 PM 02:24:00 PM 12:00:00 PM 09:36:00 AM 07:12:00 AM Time The graph above is a correl ation 04:48:00 AM 02:24:00 AM 12:00:00 AM of the time of day and number of birds observed. The general trend is that the later in the day, the more birds were observed Total Birds DO Number of Birds Observed This graph is a correlation Dissolved Oxygen in mg/l Zanati, 8

9 between the level of dissolved oxygen and the number of birds observed. The two occasions when the greatest total number of birds observed happened was also when the dissolved oxygen levels were lowest Total Birds Air Temp. Number of Birds Observed Temp in Celsius The graph above correlates total birds observed to the air temperature during the observation process. It is clear that bird numbers rose and fell with the increase and decrease in temperature Water Temp. Total Birds Number of Birds Observed Temp in Celsius This graph illustrates the Zanati, 9

10 correlation between total numbers of birds observed and water temperature at the time of observation. According to this data, it appears that there is some connection between an increase or decrease in birds at the pond and an increase or decrease in water temperature. Generally, higher water temperatures correlate to more total birds sighted at the pond. At the conclusion of this investigation, I realize that I have gained a deeper understanding of the interaction between birds and the pond environment from this process. But, like any good invcstigation should, it inspires in me several questions that are still unanswered. Would the diversity and distribution of birds be different in another season? What are the limiting factors influencing the populations of birds at the pond? What could happen to the bird populations at Mac's Pond if native fish were re-introduced to the ecosystem? I do not believe that my curiosity is quenched at the completion of this project. I will continue to observe Mac's Pond through the next several months to gain an even richer perspective on the interactions of birds and other living things in the environment, and they way they affect each other. I am fascinated by the idea of alternative equilibria in shallow lakes and pond communities, especially ones without fish. The notion that this is still a poorly understood area of study is exciting and inspiring for me in my future investigations. Zanati, 10

11 Bibliography Anderson, B. (2011). Are there fish in mac's pond? If not could there be? Bainbridge Island, WA: Islandwood Natural History Investigation. Benyus, J. (1989). The field guide to wildlife habitats of the western united states. New York, NY: Fireside Books. Caduto, M. J. (1985). Pond and brook: a guide to nature in freshwater environments. Englewood Cliffs, N.J.: Univ Pr of New England. Chaichana, R., Leah, R., & Moss, B. (July 2011). Seasonal impact of waterfowl on communities of macrophytes in a shallow lake, Aquatic Botany, Vol. 95, Iss. 1, Daley, W. (2001). Mac's pond and stream ecology/fisheries habitat assessment. Bainbridge Island, WA: Puget Sound Environmental Learning Center. Fisher, C. C. (1996). Birds of seattle and puget sound. Renton, WA: Lone Pine Publishing Lichen, P. K. (2001). Brittle stars and mudbugs: An uncommon fieldguide to northwest shorelines and wetlands. Seattle, WA: Sasquatch Books. Martin, A. C., Zim, H. S., & Nelson, A. L. (1951). American wildlife and plants: A guide to wildlife food habits. New York, NY: Dover Publications, Inc. Meerhoff, M., & Jeppesen, E. (2009). Shallow lakes and ponds. In G. Likens (Ed.), Encyclopedia of Inland Waters (pp ). Oxford, England: Academic Press. Morse, B., Aversa T. & Opperman, H. (2003) Birds of the puget sound region. Olympia, WA: R.W. Morse Co. Scheffer, M., Hosper S.H., Meijer M.L., Moss, B., & Jeppesen, E. (1993). Alternative equilibria in shallow lakes, Trends in Ecology and Evolution, Vol. 8, No. 8, Schmidt, M. (2012, February 3). Interview by S. Zanati [Personal Interview]. Bird sightings at mac's pond. Zanati, 11