An Analysis of Mockingbird Nesting Behavior in Residential Areas
Part of the Young Naturalist Awards Curriculum Collection.
When I saw a bird fly across our yard, I stopped to watch it. I saw it enter a bush between our yard and our neighbor's yard. I got a ladder and checked out the bush and saw that it contained a nest with four blue-green speckled eggs. Suddenly, a second bird swooped down and dive-bombed me! After I stumbled off the ladder, I wondered why the birds had chosen to build their nest in this suburban area between two homes, so close to residential construction and just a few hundred yards from a major road. I decided to observe the birds to find out if having their nest so close to all this activity would affect their ability to care for their nestlings. Figures 1 and 2 show how close the nest is to our next-door neighbor's home and to our driveway. The red "X" marks the bush where the nest is located.
Observations
I took some photographs of the birds to help me identify them using my field guide. I had some trouble at first figuring out whether the birds were loggerhead shrikes or mockingbirds, but close inspection revealed that they were mockingbirds. The photo shows one of the parents with an insect in its mouth. I did some research on mockingbirds and learned some interesting facts about them. Mockingbirds will not only attack humans (as they had me), but researchers have found that they can "recognize individual humans and will selectively attack them while ignoring other humans who pass by" (FloridaGardener.com). In fact, mockingbirds have been known to attack predatory birds, even bald eagles, when their territory is invaded (Doughty, 1998).
Some believe the mockingbird's bravery is the reason it has been chosen as the state bird for five states (Doughty, 1998). During the late 1700s and early 1800s, mockingbirds were popular as pets because of their beautiful singing. By the 1900s the demand for mockingbirds nearly led to their extinction. People then began to release their birds. Mockingbirds have thrived as a result; in fact, mockingbirds can now be found in Hawaii and even Canada (Coe).
On March 25, I looked in the nest and saw that there were four hatched chicks. I knew there would be much activity near the nest. Seven small children live on the cul-de-sac, in addition to several cats and large dogs. The neighborhood also has quite a bit of ongoing residential construction. I wanted to find out if all the chicks would survive in such an environment. I didn't know if their feeding schedules would be disrupted by the presence of noisy children, or if the nestlings would perhaps fall prey to neighborhood cats. I decided to do some video surveillance to monitor the birds. I could collect more data this way and at the same time minimize my disturbance of the birds.
On March 26 I set up a Canon GL2 video camera in my garage so that I could film the birds' activities. I reviewed the tape and saw that no people went near the nest during the initial hour of filming. During this initial hour, the birds spent 36 minutes and 28 seconds on the nest, and they spent 21 minutes and 33 seconds away from the nest. They made nine trips to the nest.
On March 27, I placed a second video camera (a small Canon ZRl) inside the bush near the nest. I watched from inside my garage to make sure that the birds would not abandon the nest with the camera in the bush. The adult birds returned to the nest and did not appear to be affected by the camera. I videotaped the birds for one hour. The tape showed that the birds made a total of nine trips to the nest, bringing food and removing fecal sacks. At one point during this video session, an adult bird spent 4 minutes and 54 seconds sitting on the nest. The nestlings are very young and are covered in down. Later that afternoon, I set up a camera in our garage so I could view the bush and see how the birds were affected by the people and animals in their environment. I noticed that the birds flew away when a UPS delivery person walked up to our neighbor's house and when a garbage truck went by.
On March 28 it was raining very hard, so I filmed from the garage. I noticed that during the rain the birds attempted to have a parent sitting on the nest at all times. When one parent was out hunting, the other was sitting on the nest, and they would periodically change duties. However, I noticed that when people went near the nest, the adults left the nestlings unattended, thus leaving them vulnerable to drowning. My research indicated that during torrential rains, nests can flood, drowning the nestlings (Doughty, 1998).
On March 29 I filmed from the garage again. I observed that the attending adult bird would fly away from the nest when people approached. During that one-hour period, the birds made six trips to the nest.
Analysis
On each of the dates shown on the bar graph, I filmed for one-hour periods. I then reviewed the footage and counted the number of times the parents made visits to the nest during this period of time. I also observed the parents taking away fecal sacs. The bar graph shows the number and timing of the birds' trips on the dates on which I filmed.
I did some research to determine the normal feeding patterns of the mockingbird. James Coe states that the incubation period lasts 12 to 13 days, and that the chicks are fed up to five times per hour. Similarly, Randall Breitwisch (1986) and other researchers found that the nesting period was 12 days, and that the parents brought food to nestlings on most trips to the nest. These findings are consistent with my data. Further research by Breitwisch (1989) found that feeding rates peak during the middle of the nesting period. This, too, is consistent with my data.
The photograph of the fledglings is a screenshot from the video footage taken on April 5. As you can see, the birds now have feathers and are almost ready to leave the nest.
On April 6 the fledglings left the nest. I went outside to check on the camera and saw a juvenile bird hopping along the ground. When I looked in the nest, I saw that all four juveniles had left. I watched as the four juvenile birds disappeared into the wooded lot next to our house. Over the next few days, I saw the juvenile birds flying around the neighborhood, and they now hunt in our backyard.
Conclusion
When I began this project, I was sure that all the activity near the birds' nest was bound to affect their behavior; the question was whether the birds could adapt to the disruptions and manage to provide their nestlings with the same level of feeding and protection that would be expected in a more natural habitat. Based upon my observations, the adult birds' feeding and nest-sitting activity was consistent with what other researchers have observed in more remote environments. This leads me to conclude that mockingbirds have done an excellent job of adapting to living in residential areas.
References
Breitwisch, Randall, Natasha Gottlieb, and Julia Zaias. "Behavioral Differences in Nest Visits Between Male and Female Northern Mockingbirds." The Auk 106 (October 1989): 659-665.
Breitwisch, Randall, Peter Merritt, and George Whitesides. "Parental Investment by the Northern Mockingbird: Male and Female Roles in Nestling Feeding." The Auk 103 (January 1986): 152-159.
Coe, James. "Northern Mockingbird." Cornell Laboratory of Ornithology. Retrieved from the World Wide Web on 22 March 2006.
http://www.birds.cornell.edu/BOW/NORMOC
Didier, Collin. Northern Mockingbird. Oiseaux.com. Retrieved from the World Wide Web on 22 March 2006.
http://www.oiseaux.net/passeriformes/northern.mockingbird.html
Doughty, Robin. The Mockingbird. Austin: University of Texas Press, 1998.
"Florida Mockingbird." Florida Gardener. Retrieved from the World Wide Web on 22 March 2006.
http://www.floridagardener.com/critters/Mockingbird.htm
Peterson, Roger. Birds of Texas. New York: Houghton Mifflin Company, 1960.