Northern Mockingbirds (Mimus polyglottos) are year-round residents in North Carolina and defend territories throughout the year.   In the winter, a female sometimes defends a separate territory adjacent to that of her mate from the previous summer, or a pair sometimes defends a territory together throughout the year.   Males and females can only be distinguished by behavioral differences.   In particular, only males sing.

A mockingbird spends nearly all of its time within its territory.   In behavioral studies, a territory is a defended area used exclusively (or at least mostly) by the resident and its mate.   A great variety of different species, vertebrates and invertebrates, defend territories.   In some species a territory provides only some of an individual's requirements, such as a nest site or food, but not both.   In these cases, territorial individuals must of course leave their territories to obtain their other necessities.  

In contrast, a mockingbird's territory, like those of many other small songbirds, includes all of its requirements:   places to feed, rest, sleep, and seek shelter from predators.   During the breeding season, nesting also occurs within the territory.   Consequently, each mockingbird spends nearly all of its time within its own territory.

Mockingbirds feed mostly on insects during spring and summer and fruit during fall and winter.   The red berries of the holly trees around Coker and Wilson Halls are favorite sources of food during winter.   A mockingbird defends its territory primarily against other mockingbirds, but sometimes it also attacks other birds that feed on fruit inside its territory.   Why is fruit guarded so jealously?   If food becomes too scarce during winter, a mockingbird must occasionally leave its own territory and fend for itself in other birds' territories, where it is subject to attack whenever discovered.

Territorial animals defend their territories by means of outright attacks and fights when necessary.   Much more frequent, however, are displays which serve to advertise that an individual has claimed and is prepared to defend an area.  

These advertisement displays take diverse forms in animals:   many territorial mammals use scents (secretions from special glands or simply urine or feces) to mark boundaries or conspicuous points in their territories.   Many territorial birds use long-range sounds to advertise territories.   Most birds' songs, including the mockingbird's songs, fall into this category.   A male mockingbird uses conspicuous perches as song posts from which to proclaim its presence on a territory.  

Males sing primarily from January (warm days only) through July and then again in October.   From November through February, they use another distinctive sound, a sudden harsh chat   or chat-chat-chat, to proclaim their territories especially early in the morning.   A tape-recording of a mockingbird's songs or a burst of chats,   when played from a speaker inside a mockingbird's territory, often elicits a prompt aggressive response from the resident.   What might explain this behavior?

In this exercise, you will

• map a mockingbird's territory
• determine the proportion of time it spends in different activities (its time budget)
• observe behavior used to advertise and to defend its territory
• conduct an experiment to determine some characteristics of stimuli that evoke territorial aggression

Procedure -- Advance Preparation

Field work almost always requires preparation in advance.   A week before we actually start to study mockingbirds, you will have to get ready:

• load batteries into the cassette tape players and the speaker/amplifiers.   (Also remove the batteries the week after they are used.)

• learn how to connect the tape-recorder to the speaker/amplifier and how to adjust the volume.

• design a data sheet to collect information on time budgets and another one to collect information on the responses to playback.   All classes might use the same standardized sheet -- but everyone should think about how to design it and perhaps should prepare their own sheets.

• check the binoculars.   Learn how to focus both eyepieces and to adjust the distance between eyepieces so you see a single, clearly focused circle.   You should check them for alignment by holding the binocs a foot or so in front of your eyes and focusing on some distant horizontal line (the eves of a building, for instance).   If the binocs are in alignment, the horizontal line will appear at the same level in both eyepieces.

• learn how to identify mockingbirds!   They are gray birds with conspicuous white spots in the wings and white edges of the tail.   Many (but not all) mockingbirds on campus have colored plastic bands on their legs.

Procedure -- Week I

Work in groups of 4-5.   Use a paper and pencil for recording observations, a watch to time behavior, and binoculars.   Each group will record the behavior of one mockingbird (or a pair) for one hour.  

Two students will serve as observers with responsibility for keeping the bird in sight (or knowing its location, if it is in a bush out of sight) at all times.   A third person will record the locations of the bird on a map.   The fourth person will keep a written account of the bird's behavior, and the fifth person will serve as timer.   Everybody should take a turn looking at your subject with the binoculars -- does it have colored plastic bands on its legs?

In recording the behavior of an animal, we need to take into account two kinds of activites.   Behavioral events are actions that take place essentially instantaneously (or are too brief to allow us to time their duration), such as eating an item of food or attacking an opponent.   Behavioral states are activities that last long enough for us to time their duration,   such as resting on a perch, singing or preening continuously, or displaying repeatedly to a neighbor at a boundary.   When you make a record of your mockingbird's activities, you will want to count all events but time the duration of all states.

To estimate the time an individual spends in different states, you should use scan sampling, the procedure used in the exercise on fish schooling.   Instead of recording the time at the start and stop of each behavioral state, record the bird's behavioral state every 10 seconds (the person serving as timer can help here).   In one hour you will then have 6 observations/minute X 60 minutes = 360 scan observations at 10-second intervals.   How can you use this information to estimate the proportion of time spent in each behavioral state?

You also will want to pay attention to a bird's locations and conspicuousness.   Perching on a high bare branch (conspicuous both to other mockingbirds and possible predators) is not likely to be equivalent, from the point of view of a mockingbird, to perching out of sight in the middle of a dense bush.   Think like your mockingbird when you decide what to record about its behavior!

Take notes that will allow you to determine the following:

• Proportion of time spent by your subject in different behavioral states:   perching in conspicuous places, perching out of sight (but in a location that you know for sure), preening, singing, foraging for food on the ground, in trees, and so forth)

• Rates of behavioral events.   Rates are frequencies/minute of observation (or 10 minutes of observation, if more convenient):   food items eaten, flights, chases or swoops at mockingbirds, chases of other species, sun-bathing, wing-flashing while hunting for food on the ground, chat   calls, and so forth

• A map of the bird's conspicuous perches, other perches, and feeding sites

Especially important are the locations at which your subject attacks or challenges opponents (if any).   Also include the locations of other mockingbirds that you notice while watching your subject.   Then determine the area defended by your subject, the area used exclusively by your subject, and the total area used by your subject.   Do these three areas coincide?

After recording your observations for one hour, prepare the above three summaries.   You should have made a start in understanding your subject's territorial behavior.   Give your summaries to your Teaching Assistant.

Procedure -- Week II

This week you will conduct an experiment with playbacks of tape-recordings.   During the week or two before this exercise, you will have a chance to check all the equipment we use.  

During this exercise, you will again observe your bird's behavior for one hour and make a map of its territory, in order to obtain some additional information about your subject's behavior and the limits of the territory.   Afterwards, you will use playbacks of tape-recordings to create the impression of different kinds of intruders in the territory.  

Each group will present two different tapes, selected from the four listed below.   Different groups will present different combinations, so you can compare the mockingbirds' responses to all four tapes:

1. a mockingbird's songs near the center of the territory

2. a mockingbird's songs near (but inside) the boundary

3. a mockingbird's chat calls near the center of the territory

4. another common species' songs near the center of the territory (we use the Carolina Wren, a species nearly as numerous as the Northern Mockingbird on campus) Each tape has 10 minutes of recording.   You should make observations for 10 minutes before and after the playback as well (see below).   Then wait at least 10 minutes, during which you should move the speaker at least 15 m (50 feet), before the next playback.   If appropriate, after selecting positions for the speaker, flip a coin to determine which tape and which position to use first.

   The loudness of the playback is a important variable in these experiments.   Too quiet and the playback might not be heard.   Too loud and the mockingbird might conclude that its territory has just been invaded by the mockingbird equivalent of Godzilla!   Encourage students to use their own ears during the playbacks to adjust the volume.   It is no use adjusting volume in the lab (sound reverberates in the room and makes any estimates of loudness useless outdoors).

   As before, use scan sampling to estimate durations of behavioral states and counts to determine the frequencies of behavioral events.   For these experiments, you should also record the latencies of conspicuous responses (the time from the start of playback until the subject's first reaction).

   Use these procedures to obtain at least the following four measures of your subject's behavior, during the three intervals (10 minutes before playback starts, 10 minutes during playback, and 10 minutes after playback ends), for each playback:

   • time spent within 10 m (just over 10 yards) of the speaker

   • latency to approach within 10 m after the start of playback

   • closest approach during playback

   • number of songs.
   Did some states or events increase during or after playback?   Or decrease?   By subtracting the measures of your subject's behavior before playback from the same measures during and after playback, you can determine how much its behavior changed.  

   Use the results from your entire section (or all sections) to compare behavior before, during, and after the playback.   Use simple statistics (see the supplement to this manual).

   Also compare responses to the three different kinds of playback.   How would you use simple statistics in this case?

   Questions

   Do mockingbirds respond to conspecific (same species) calls as much as to songs?  

   Do they respond to other species' songs as much as to conspecific songs?

   How do responses to playbacks resemble responses to natural intruders?   How do they differ?

   Why do certain stimuli evoke territorial aggression?

   Why do we record data before and after the playback as well as during it?

   Why do we choose positions for the speaker and then flip a coin to determine which to use first?

   Why do we move the speaker between playbacks?

   

   References

   Breitwisch, R., M. Diaz, N. Gottlieb, R. Lee, and J. Zaias.   1986.   Defense of fall territories by mated and unmated northern mockingbirds in southern Florida.   Journal of Field Ornithology 57:   16-21.

   Breitwisch, R., M. Diaz, and R. Lee.   1987.   Foraging efficiencies and techniques of juvenile and adult northern mockingbirds (Mimus polyglottos).   Behaviour 101:   225-235.

   Derrickson, K. C.   1987.   Behavioral correlates of song types of the northern mockingbird (Mimus polyglottos).   Ethology 74:   21-32.

   Derrickson, K.C.   1987.   Yearly and situational changes in the estimate of repertoire size in Northen Mockingbirds (Mimus polyglottos).   Ethology 74:   21-32.

   Derrickson, K.C. and Breitwisch, R.   1992.   Northern Mockingbird (Mimus polygottos).   In A. Poole, P. Stettenheim, and F. Gill, Eds.   Birds of North America.   Philadelphia, Academy of Natural Sciences, and Washington, D.C., American Ornithologist's Union.   Pp. 2-26.

   Godard, R.   1991.   Long-term memory of individual neighbours in a migratory songbird.   Nature 350:   228-229.

   Godard, R.   1993.   Tit for tat among neighboring hooded warblers.   Behavioral Ecology and Sociobiology 33:   45-50.

   Hailman, J. P.   1960.   Hostile dancing and fall territory of a color-banded mockingbird.   Condor 62:   464-468.

   Howard, R. D.   1974.   The influence of sexual selection and interspecific competitioon on mockingbird song.   Evolution 28:   428-438.

   Laskey, A. R.   1935.   Mockingbird life history studies.   Auk 57:   370-381.

   Laskey, A. R.   1962.   Breeding biology of mockingbirds.   Auk 79:   596-606.

   Logan, C.   1983.   Reproductively dependent song cyclicity in mated male mockingbirds   (Mimus polyglottos).   Auk 100:   404-413.

   Logan, C.   1985.   Mockingbird use of chatbursts with neighbors versus strangers.   Journal of Field Ornithology 56:   69-71.

   Logan, C.A. and Hyatt, L.E.   1991.   Mate attraction by autumnal song in the northern mockingbird (Mimus polyglottos).   Auk 108:   429-432.

   Logan, C.A., Hyatt, L.E., and Gregorcyk, L.   1990.   Song playback initiates nest building during clutch overlap in mockingbirds (Mimus polyglottos).   Animal Behavior 39:   943-953.

   Selander, R., and D. Hunter.   1960.   On the functions of wingflashing in mockingbirds.   Wilson Bulletin 72:   340-345.