[求助] gwd 28-5

Social learning in animals is said to occur when direct or indirect social 

interaction facilitates the acquisition of a novel behavior. It usually

 takes the form of an experienced animal (the demonstrator) performing

 a behavior such that the naïve animal (the observer) subsequently expresses 

the same behavior sooner, or more completely, than it would have otherwise. 

One example of social learning is the acquisition of preferences for novel 

foods. Some experiments have suggested that among mammals, social learning 

facilitates the identification of beneficial food items, but that among birds,

 social learning helps animals avoid toxic substances. For example, one study

 showed that when red-wing blackbirds observed others consuming a colored food 

(30) or a food in a distinctly marked container and then becoming ill, they 

subsequently avoided food associated with that color (35) or container. 

Another experiment showed that house sparrows consumed less red food after 

they observed others eating (40) red food that was treated so as to be noxious. 

 Studies on non-avian species have not produced similar results, leading researchers 

to speculate that avian social learning may be fundamentally different from that of mammals.

But Sherwin's recent (50) experiments with domestic hens do not support the 

notion that avian social learning necessarily facilitates aversion to novel 

(55) foods that are noxious or toxic. Even when demonstrator hens reacted with

 obvious disgust to a specific food, via vigorous head (60) shaking and bill

 wiping, there was no evidence that observers subsequently avoided eating 

that food. Sherwin's research team speculated that ecological or social 

constraints during the evolution of this species might have resulted in

 there being little benefit from the social learning of atability, for 

instance, selective pressures for this mode of learning would be reduced 

if the birds rarely encountered noxious or toxic food or rarely interacted

 after eating such food, or if the consequences of ingestion were minimal.

 (80) In a related experiment the same researchers showed that if observer

 hens watched demonstrator hens react favorably to food of a particular 

color, then observer hens ate more food of that color than they ate of

 food of other colors. These results confirmed that avian species can 

develop preferences for palatable food through social learning.

28-5: According to the passage, which of the following is true of the 
experiments on domestic hens conducted by Sherwin’s research team?
 
A: Only a small number of observer hens appeared to learn to avoid food that
 was demonstrated by other hens to be noxious.
B: Observer hens ingested food preferentially only after numerous instances
 of witnessing demonstrator hens preferentially ingest that type of food.
C: Observer hens appeared unable to recognize when demonstrator hens 
found a particular food especially palatable.
D: Observer hens appeared unable to recognize when demonstrator hens 
found a particular food especially palatable.
E: Demonstrator hens altered their behavior less obviously in response 
 
to noxious foods than in response to highly palatable foods.

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