Urban Birds in Central Park

Tufted Titmouse in the Ramble

Ever since I was little, I have always wanted to be able to fly. Who hasn’t tried to chase pigeons and been amazed at them flying away? Birds are so different from humans and other mammals. Beautiful songbirds always visit my grandma’s backyard. I have spent hours just watching them peck at the feeders and at the leaves.

Northern Cardinal in the Ramble

Until recently, I had only associated bird watching with the countryside. After seeing a red-tailed hawk in a park near my house, and two blue jays in a school courtyard, I became interested in how these birds make a home in the busy, dangerous city of New York. Do some birds thrive more than others? Where do birds live in the city? These questions inspired me to focus my investigation on the urban habitats of birds, and to take a survey of the birds in Central Park.

Question

How does habitat affect the diversity and number of bird species in Central Park?

Hypothesis

My hypothesis is that the habitat with the greatest natural resources and the least human intervention will support the largest populations and greatest diversity of birds. I believe this because trees, food, water and plants are essential to the lives of birds. They need these elements to survive. Human intervention can mean a loss of these natural resources. Therefore, I expect to see more birds in habitats that provide these essential components.

Background Research

Birds are very abundant in North America. There are 230 species of birds in Central Park alone (Johnson, 1). Different species of birds live in or depend on different habitats. Some birds, such as house sparrows, song sparrows, white-throated sparrows, rock doves, mourning doves, red-tailed hawks, American crows and European starlings, prefer open spaces (Johnson, 3). Other birds, like woodpeckers, magnolia warblers, black-and-white warblers, northern cardinals, blue jays, Baltimore orioles and house finches, prefer woodlands (Johnson, 2). For all of these species, trees and a reliable source of water are essential.

Birds have similar necessities to people. In a habitat, they need food, water and shelter (“Bird Habitat Necessities”). Habitats that provide a lot of these necessities will probably be home to birds. Birds prefer native, natural resources to non-natural ones (“Bird Habitat Necessities”).

I contacted Graham Chisholm, the executive director of Audubon California, about strategies for my investigation. He suggested that I visit different parts of Central Park to observe birds because Central Park has a lot of variation in habitat. He also suggested that I compare my results to the Audubon Annual Christmas Bird Count, also taken in Central Park.

Experimental Design

When bird watching, it is important to bring binoculars, a field guide, a notebook and a pencil. If you cannot identify a bird, you can take a picture and identify it later (Hume). You have to be patient. I found a map of different places in Central Park that are good for bird watching. Within the borders of Central Park, many different habitats can be found (Johnson, 7).

I went out twice to conduct my first observations of the birds in November, but I did not have a systematic procedure and process. I did not include the data from these initial explorations because it would be impossible to draw any conclusions from them, as I did not record the properties of the habitat. But these expeditions into the field did show me what I needed to prepare for my official experiment.

I went to five main locations (and their surrounding areas) during my study. The first area was the North Ramble. The North Ramble is an isolated, hilly woodland area in the center of the park. There is a small creek running through it. I listed it as a 4 on my tree density scale. The next location was the Harlem Meer, an eleven-acre, man-made lake at the northeast corner of the park. There is a hill with trees and a boathouse nearby. There is also some street traffic and traffic from the park roadway. Since it is a lake, it is a 0 for tree density, but in the surrounding areas, it was a 2 or a 3. I also visited the Central Park Lake. The eighteen-acre lake is situated in the center of the park near the Ramble. It is surrounded by trees and woodlands and there is relatively little traffic. At the Central Park Lake, the tree density is 0, but I rated its surrounding a 2 or a 3. The North Woods was another habitat I visited. Located in the northeast corner it is the park’s most secluded area. It is a heavily wooded area and there is a small stream. I rated it a 3.5 on the tree density scale. The final location was the Great Hill. The Great Hill is an open hilltop meadow surrounded by elm trees in the northwestern part of the park. I rated it a 3 on the tree density scale.

This is the description of my scale for the density of trees in an area:

Materials

• Notebook
• Pen
• Camera
• Binoculars
• Bird identification guide
• Tape measure

Procedure

The map shows the places that I went to in Central Park to do my investigation.

1. I went to the Ramble in Central Park.
2. I recorded tree density and tree type. To record tree density, I created a scale from 0-5 (see table below).
3. I selected three 1-meter-by-1-meter quadrants and measured the depth of the leaf litter. To measure leaf litter, I took a ruler and measured the depth from the ground to the top of the leaves.
4. I recorded the type and percentage of plant cover (either <50% or >50%).
5. I then recorded any invertebrates like worms found in the leaf litter.
6. I observed each area for 20 minutes, recording all bird sightings.
7. I repeated this process with the North Ramble, the Central Park Lake, the Harlem Meer and its surrounding area, the North Woods and then the Great Hill. (See the map).

Variables and Sample Size

My independent variable is the habitat, each habitat having its own combination of tree density, depth of leaf litter, number of invertebrates, etc. The dependent variables are the bird species living there and the number of birds. Since I was doing this experiment in nature, it was difficult to control any of the variables. Instead, I tried to record and account for many of the variables I saw so that I would have an understanding of the characteristics of the habitat. I did control the tree density scale and the amount of time I spent observing. The use of binoculars is also a variable I controlled. My sample size was five locations over two days.

Results

Species of Birds in Different Habitats

Data Summary

In total, I observed nine different species of birds in the areas I explored. I looked in both woodland and lake environments. I found that tufted titmice were only found in places that have a tree density scale of more than 4. In one area a large group of titmice were seen only in evergreens. The tree density scale did not affect the total number of birds I saw. I found that American robins were found only in places that had leaf litter above three inches. I am not sure whether the depth of leaf litter affected the kinds of birds I saw, because all the woodland areas I observed had leaf litter of more than two inches; any depth under one inch was a lake area. The number of birds (excluding water birds) found near a lake or creek was mostly equal to the number of birds not near a water source.

This is the graph for all of the species I saw in my study. The largest number of any species was the mallards in the Harlem Meer. The habitat with the most birds was the Lake, and the habitat with greatest variety of species was the North Woods. The North Woods also had the deepest leaf litter.

Analysis

The outlier tree with leaves on it

My original hypothesis was that the habitat with the most trees and leaf litter would be the most populous habitat for birds. This was partly confirmed by the fact that the places with a high tree density had more birds. My data also suggested that some bird species find food in the leaf litter.

My data was not sufficient to show clear correlations between particular species and a particular aspect of a habitat. However, I did reach some conclusions. I found that birds, especially the tufted titmice, populated the two or three trees that were evergreens. This suggests that these trees might help non-migratory birds survive during the winter. No other trees had leaves. I also noticed that the North Woods, the habitat with the deepest leaf litter, had the greatest variety of species. This suggests that places with deeper leaf litter attract more types of birds.

My data journal

American robins were found only in places that had leaf litter above three inches. This could show that they can find food in the leaf litter, or that it is valuable to them in some other way. I can also suggest that tufted titmice have food sources in the trees, because they were only found in places with a tree density scale of 4.

I found that having a water source nearby probably does not affect the number of birds in the area. It does affect the bird species found, because only water birds like mallards and gulls were found at the Lake. This surprised me, because I thought that birds would travel into other areas even if it were not their normal habitat. I thought that water birds, especially in the diverse habitat of Central Park, would travel and be found in places other than the lakes and ponds or right next to lakes or ponds.

I noticed two major differences in the birds I saw. The water birds were always in flocks, and the non-water birds were not. The only birds I saw in flocks were mallards and gulls, both water birds. Therefore, it would be more meaningful to make separate graphs for birds that were found in flocks and birds that were not. This is because the 30 to 50 birds traveling together in flocks provide the misleading impression that each has come of its own volition, instead of being driven by flocking behavior. I took out the water/flocking birds, and made a new graph. Removing flocking birds makes it more obvious which birds were attracted to which habitat.

This graph shows that the tufted titmouse was very prominent in the North Ramble. This species was found only there, and was the only species found there. This indicates that some quality of the North Ramble is attractive to the tufted titmouse, because the 20 birds seen there were all separate, not in a flock. It could be that the North Ramble was the only location I visited that had evergreens.

Sources of Error

My experiment could have been flawed because there are sources of error. A source of error could be the fact that my observations were conducted in the winter, so birds may not have been active. I did not control the variable of time, meaning that I went once in the morning and once in the afternoon, and that could have affected my results, because birds could be more active at a certain time. It is also possible that I misidentified birds. For example, when I compared my results to the results of the Audubon Christmas Bird Count, I saw a major difference. Their count was on a much bigger scale and time period than mine, and they found 8 song sparrows in total and 674 white-throated sparrows. If I found 10 song sparrows in my smaller experiment, it could show that I incorrectly identified some white-throated sparrows as song sparrows.

Further Investigation

If I were to do this investigation again, I would choose a more specific aspect (leaf litter, tree density, etc.) of the birds’ habitat and focus in on habitats that have varying degrees of that aspect. I would also start collecting data much earlier, and do the study in the spring or summer. I would also like to visit more places than I did during this experiment, so that I could gather more conclusive results.

I have some questions that still remain. First of all, I want to know if the results are more conclusive during the summer. Second, since I started to see a bit of a pattern with the leaf litter, I should visit places that have more variation in leaf litter to determine whether or not the leaf litter affected the number and species of birds. Some of my other questions are: Do birds rely on evergreens trees during the winter? Are tufted titmice found in other areas? Do birds travel the whole city, or stay in their areas?

Conclusion

Now when I see a bird on the street or in the park, I don’t just see a bird: I see a specific species of bird that I know how to identify. I notice what it is eating, and where it is, and the type of habitat. These are elements I never noticed before beginning my investigation. In conclusion, the Young Naturalist Award investigation helped me become a more observant person, and it made me see birds in a more scientific way.

Bibliography

“Audubon Annual Count in Central Park Finds 5,721 Birds.” National Audubon Society, 19 Dec 2012. Retrieved from the World Wide Web on 25 Feb 2013. www.audubon.org

“Bird Habitat Necessities.” Audubon at Home. National Audubon Society. Retrieved from the World Wide Web on 6 Feb 2013. http://web4.audubon.org/bird/at_home/HealthyYard_BirdHabitat.html

Hume, Rob. Birdwatching. New York: Smithsonian, 2005.

Johnson, Elizabeth A. “Kid’s Guide to the Birds of Central Park.” AMNH. Retrieved from the World Wide Web on 6 Feb 2013. http://www.amnh.org/our-research/center-for-biodiversity-conservation/publications/general-interest/kid-s-guide-to-the-birds-of-central-park