A lecture from a life sciences class (4)
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Listen to part of a lecture from a life sciences class.
Prof: Birds use communication for a variety of reasons: to repel other birds, to attract other birds, to find family members, and to alert other birds to danger. They communicate with each other in unique and fascinating methods, which include singing, dancing and strutting. Biologists have only recently begun to compre [false start] to understand the implications of some of these, er, interesting behaviors.
Verbally, birds make noises that scientists label "calls" and "songs." Types of calls are cheeps, honks, squawks, chips -- I mean chirps -- and tweets. Now, most birds make only a single call, but some birds, known as songbirds, are able to craft more complex tunes. In recent years biologists have used tape recorders to better analyze bird noises and study other bird's re, responses to them. They have discovered that single calls communicate simple messages, such as "Here I am," or "Watch out for that hawk!" Um, songs, on the other hand, are performed, or usually performed, only by males, and for one of two specific reasons: to defend territory or to find a mate. In one experiment, scientists removed all the male birds of one species from a certain area and replaced them with tape recordings of their songs. Other males from that species heard the recordings and wouldn't enter that area.
Biologists have also discovered that male birds will sometimes have a singing con, uh, singing duel to determine which one gets the best territory. One bird will sing, and then the other will answer with the same song or a similar one. This counter-singing will go back and forth until one bird "wins," though no one yet knows how the champion is determined. Kind of like an avian "American Idol," huh? OK. In another experiment, biologists put dummies of one type of bird in a field. Half of the dummies played a recorded version of that bird's mating song, while the other dummies were kept silent. Female birds flocked to the singing dummies and ignored the quiet ones. I guess girl birds don't go for the strong, silent type. [groans] Although female songbirds don't usually sing, they will sometimes imitate a male's song to signal to their mate that an en, er, predator is coming. The male will think another bird is encroaching on its territory and hurry back to protect its nest.
Biologists know that baby birds make a cheeping sound to indicate to their parents that they are hungry or hurt, a behavior that they term "begging." Different kinds of birds beg with higher or lower frequencies, depending on the location of their nests. Birds with nests in trees beg louder, using a lower frequency, because they have less worry of attracting predators. Birds with nests on the ground beg with a higher frequency that doesn't carry the sound as far, because they are more vulnerable to a predator's attack. Um, begging birds compete for their mother's attention, to be fed first or to get extra food or care. Usually, a baby bird that has had enough to eat will quit begging loudly. However, biologists have recently found that this is not always the case. New studies indicate that parents often give more food and attention to the most persistent beggars -- the youngsters who cheep longest and loudest. Ironically, human babies often exhibit the same kind of behavior. We call in whining. [laughter]
OK [chuckles]. Birds also use a series of non-verbal signals, or body language, to communicate various intentions. Many male birds will perform some type of dance to attract a mate. Here is the male booby bird, for example. He alternately lifts its blue webbed feet high in the air until a female booby comes and touches his neck with her beak. Here she comes. All right dude. Good job! Other species attract mates by flashing feathers with extraordinary colors, such as a peacock's tail and a tragopan's blue-and-red chest. A male will usually puff up the colored parts of his body and strut near the female, hoping to impress her. Male bower birds build small nests that they decorate with colorful objects, such as uh, shells and, um, buttons. When a female comes near, the male bower will pick up one of the objects in his beak and strut around with it. When male birds succeed in attracting a female, the new pair will often perform an intricate dance together to indicate their acceptance of each other. A species of water bird called grebes perform a ritual in which they ruffle their feathers, shake their heads and offer each other plants to eat.
What is the main topic of the lecture?
How do male birds use songs?
Why does the professor discuss an experiment with dummies?
What can be inferred when the professor says this: "Here is the male booby bird"?
What is true of baby birds whose nests are in trees?
What does the professor imply about birds' communication?