Laboratory Exercises in Animal Behavior - Case Study
Before we begin our exercises in animal behavior, it might be helpful to look at a case study as an example of the concepts and principles we have now briefly discussed. The second author of this manual has studied the behavior of the red-winged blackbird (Agelaius phoeniceus) for over 20 years, so it seems natural (to him) to use this species for our case study. The first author still remembers the cold and wet (and very early) morning when she was introduced to red-winged blackbirds while taking zoology from the second author. The second author can close his eyes and remember vividly his first visit to a red-winged blackbird marsh in 1973.
Red-winged Blackbirds
Red-winged blackbirds are familiar and common birds throughout most of North America. Most people notice them in the summer as they drive along highways-there seems to be one on every fence post. Some people have had "close encounters" with red-winged blackbirds, which can swoop at and even hit people who stray too close to active nests. If you live in a part of the United States where red-winged blackbirds are common (you can look in one of the many bird identification guides to find out whether you live in such an area), you can go to a marsh or field in early spring and watch their behavior. The first thing you must know is that the name of the species describes the adult (at least two years old) males only. Females are not black with red patches on their wings; females are brown and streaked below-they look something like big sparrows. Males that hatched in the previous spring (one-year-olds) vary in appearance, but most look like a cross between an adult male and a female. They are generally black but have lots of brown streaks or patches, and their wing patches ("epaulets") usually have brown or black spots and are more orange than red.
In Illinois and Wisconsin, where the authors of this manual live, male red-winged blackbirds return from their wintering grounds in late February and early March. If you watch males soon after they return, you quickly notice several aspects of their behavior. It is hard not to be struck by their beauty. The jet black males seem to "show off" their prominent red (edged with yellow) epaulets by extending their wings, lowering and spreading their tails, and puffing out their feathers-the epaulets seem like beacons. Usually, they make an almost eerie noise as the show their epaulets. This sound is the male's song, which is described by animal behaviorists with the phrase "conk-a-ree" (if you library has an audio collection, you can hear the song of the red-winged blackbird on one of the sets of recordings of the birds of North America). The movements that feature the epaulets and the song are together referred to as the "song spread" display by animal behaviorists.
It won't take you long to notice that song spreads are given very often (as many as 10 times per minute), and that each males seems to restrict his performances of these displays to a specific set of perches. If you continue watching carefully, you will notice that each male seems to have his own space, within which he sings and displays, and into which other males only occasionally venture. You are observing an example of what animal behaviorists call "territorial behavior," and male red-winged blackbirds offer a classic example of territoriality.
Questions about Behavior
Let's think about the song spread display in terms of the four questions that animal behaviorists ask.
First, how is it caused? Usually, the males just seem to sing and display-there doesn't seem to be anything in particular that stimulates them to sing, as Nike would say, they just do it. Sometimes, however, it is clear that they are responding to a particular stimulus, for example the approach of another male. One animal behaviorist (Jerram Brown) was curious about the neural control of singing, so he stimulated areas of a red-winged blackbird's brain with mild electric current in an attempt to get the bird to sing. Another animal behaviorist (William Searcy) was interested in the hormonal causes of singing, so he put different kinds of hormones in red-winged blackbirds to see whether singing would increase, decrease, or remain the same.
Second, how does it develop? One animal behaviorist (Peter Marler) suspected that the song of the red-winged blackbird, like the songs of other species of song birds, is learned. To investigate song development, he raised young red-winged blackbirds in sound-proof chambers in which they either heard nothing or they listened to recordings of normal song.
Third, how has it evolved? An animal behaviorist (Rebecca Irwin) looked at the evolutionary lineage to which red-winged blackbirds belong in an attempt to understand the evolution of their singing behavior.
Fourth, what is the function of singing? Two animal behaviorists (Frank Peek and Douglas Smith) used surgery to make red-winged blackbirds mute (actually, they could still make noise, but they couldn't sing the normal song) to see whether loss of song affected their ability to defend their territories. The second author of this manual captured red-winged blackbirds and held them in cages temporarily while he played tape recorded songs through speakers to see if the broadcasts alone could defend the territories.
Animal Behavior and Red-winged Blackbirds
Although these (and many other studies) of the behavior of red-winged blackbirds have addressed different questions using many different methods, all were based on the principles of scientific investigation. The authors of these studies used existing information to formulate hypotheses (proposed answers to one of the four questions of animal behavior), and then tested them by conducting observations or experiments that could falsify critical predictions of the hypotheses. This process has substantially increased our understanding of this species in particular, and of behavioral phenomena in general, and the process has been "snowballing." As we investigate more, we learn more about a species or a phenomenon, but we also raise more questions and propose more hypotheses, which stimulate more investigation. At this point, even though there have been literally thousands of studies of red-winged blackbirds, we still have much to learn, and the number of studies is still increasing. Animal behaviorists in particular, and scientists in general, are powerfully curious and driven to satisfy their curiosity. That is why science is dynamic and fun.
