Saturday, October 27, 2012

Black Rats of Israel

    Taking a shift away from my review article last week, I am going to focus on an experimental paper this week.  The paper is titled "Cultural Transmission of Feeding Behavior in the Black Rat (Rattus rattus)" by Joseph Terkel of Tel Aviv University.  This one talks about black rats, found in Israel, that were discovered to be pulling pine cones from tree branches, stripping all the scales and getting to the seeds located inside.  The experimenters were initially shocked at the behavior that they witnessed, since there were no squirrels in Israel, but they laid out a series of traps and discovered that it was these black rats doing the dirty work.
     The researchers then conducted a series of experiments to determine how these black rats had learned this behavior.  They wanted to know if the pine cone opening behavior was transmitted genetically or acquired by learning, and whether they learned it through trial and error or through imitation.
     The first experiments were done to examine trial and error learning.  Naive (those who had never stripped pine cones) rats before were not given food for 48 hours to make sure that they were hungry, and then put in a cage with pine cones.  The rats certainly did try to open the pine cones, but not a single rat (out of the 32 tested) were able to successfully strip the pine cones.  The primary response of the rats was to gnaw at the cones, which is the way rats typical approach eating their food.  In addition, a second experiment was done where naive, adult rats were paired with experienced pine cone strippers of the same sex.  This, too, proved ineffective as the naive rats were unable to learn the technique necessary to the strip the pine cones.  A third experiment was done where naive pups, were fed milk from their naive mothers who were fed pine seeds.  This was done to see if there was some flavor cue that would enhance the young rats' abilities to strip a pine cone.  This too proved ineffective.
    The most effective type of learning occurred when pups who were born to stripper mothers (mothers who knew how to strip pine cones) or born to naive parents but were reared by a stripper mother were able to socially learn the stripping behavior.  This is distinctly different from the previous experiments conducted because the rats are all young (pups) and have the plasticity to learn new behaviors, unlike adult rats who are more fixed in their ways.  Also, the rats got paired up with a female stripper mother, as opposed to a rat of the same sex.  The influence a mother has over pups is much greater than one an experienced adult has over other adults.  Pups of any species must look to the mother to learn how to feed and forage for food, otherwise they will die.  It is this necessity and situation that causes the pups to socially learn the behavior from mothers, whereas adult rats do not learn the behavior from other rats, instead opting to gnaw at the pine cones - a strategy that has provided weak results.
       I am impressed with how extensive the research conducted was.  The researchers also wanted to test how naive rats come to learn the stripping behavior, so they decided to assist the rats and give them clues to opening the pine cones.  They gave rats a series of cones with different grades of the scales stripped.  For example, they gave rats cones with 4 scales stripped off and found that they were able to finish the job of stripping the pine cone and get to the seeds inside.  When they were given a fully intact pine cone afterwards, they were unable to strip the pine cone, however.  It was found that ninety percent of the rats were able to open pine cones, when a steadily decreasing number of scales was presented to them.  For example, one week they were given a pine cone with 4 scales removed, then 3, then 2, then 1, and the rats were able to open them all.  It would have been interesting to see if the rats were able to open the pine cones with a gradually increasing order of the scales removed to see if they were able to open a pine cone with 1 scale removed, as opposed to starting off with the easiest task of opening up a pine cone with 4 scales removed.
     Finally, the research went into another style of opening the pine cones - a method called shaving. In this method, the rats would strip one side of the pine cones and extract the seeds from that side, as opposed to stripping the entire pine cone.  When "assisting" the rats, this time by pulling 4 scales off the cone, but only going halfway around the circumference of the base, they were able to complete the task by stripping one side of the pine cones and extra the seeds from that side only.  This goes to show you that rats are able to learn to strip cones based on what they see in nature.  If their earliest experiences with pine cones came from seeing scales stripped from one side, then they would shave the cones.  If their experiences came from seeing the scales stripped all the way around, then they would also strip the cones all the way around.  Animals are very social creatures, so observation and plasticity at a young age plays a very important role in development.  The article I read made a great point about how "In nature, the likelihood that a pup will encounter  a partially opened cone in the vicinity of its mother, is much greater than the likelihood of an adult finding a partially opened cone.  This experiment, therefore, stimulates a condition under which the feeding technique could be acquired and passed on to the next generation."
     There are two ways of testing that can be done to see how rats acquire the ability to strip pine cones - observation and experimental testing.  Both have their advantages and disadvantages which I wanted to discuss briefly.  The observational approach would provide more accurate results as the exact method by which rats acquire their skills, but it is often difficult to carry out because the rats feed at night, and in areas that are not always accessible.  On the other hand, experimental approaches are effective because any variable can be manipulated and tested, but the external validity of these tests is not very high, since rats are not in a cage or in a laboratory in the real world.  As the experimenters alluded to quite a few times, the rats were shy or scared to strip cones while people were watching them, and sometimes it seemed like they became desperate to do something different because they were starving and people were watching.  Maybe the Clever Hans phenomenon was at play in these experiments.  This term comes from the the situation whereby a horse seemed to know how to count and add numbers, but was actually just responding to the unintentional cues given by the experimenter whenever it had reached a correct answer.  Maybe the experimenters in this study let out a sigh of relief when the rats began stripping away the scales of the cones, and that was how they learned the behavior.  Although it may be a legitimate study, you can never know for sure exactly what is going on in nature simply through experimental procedures.
     In conclusion, rat pups were seen to be most capable of social learning (through observation and trial) when reared by a mother with pine cone stripping experience.  Many rats have been seen to take pine cones from their mothers after the mother has partially stripped the scales off.  This further supports the experiments conducted in this study where rats learned how to strip a pine cone after they were partially stripped already.  And, of course, it was concluded that the stripping behavior was not passed on genetically as was originally postulated.  The first rats to ever learn this behavior must have seen some pine cones in nature that had lost part of their scales and experimented with ripping the scales off completely.  I think these experimenters did an excellent job breaking down the process at every level and continually investigating the causes and factors at play for social learning.  This was one of the best experiments I had ever read about as no corners were cut and a multi-layer investigation was conducted to finally learn how it is that rats do what they do.


Terkel, Joseph. Cultural Transmission of Feeding Behavior in the Black Rat (Rattus rattus). Tel Aviv,  
            Tel Aviv University, 1996.

Monday, October 22, 2012

Foraging Mechanisms and Social Influences

Hello again.
   I have started up my blog post for Psych 118, Comparative Psychology and will be blogging about a variety of topics that differ markedly from my posts in the spring.  I will be writing a comparative analysis on the foraging and eating mechanisms and behaviors between different animals.  I will touch on lineages ranging from the earliest jellyfish when nervous systems were first developing to the more advanced primates and humans.  So far in class we have begun talking about how animals have been evolving and changing over time from the earliest porifera (sponges), to the cnidarians with their primitive nerve nets and on to the mammals - including apes and humans.  The evolutionary trend has been towards developing larger brains that occupy greater volumes relative to body size.  It is this trend that has helped great apes and humans acquire skills to forage for food more effectively.  Some of the topics I will discuss about include using tools to search for food, observing and imitating others, and other social influences that affect the way animals search for food.
    The primary research article I will be discussing today is entitled "Social influences on foraging in vertebrates: causal mechanisms and adaptive functions" by Bennett Galef and Luc-Alain Giraldeau.  It is a summary on 20 years of research on the causes and function of social influences on foraging by animals.  It is interesting to note the different types of behaviors that you find and how they affect foraging behavior in the species.  As animals engage in their daily rituals, which involve searching for food, they provide information for others, which attracts them and guides them.  For example when an agouti gnaws on a nut, the rasping sound it produces attracts other agoutis to find the feeding site as well.  In this way, one member of a pack is benefitting the whole group by alerting the others.  Similarly, rats also engage in social behavior that helps offspring or other members of the group.  When food is found at a source, adult rats deposit certain chemicals on the feeding site and the foods that they have been eating.  This is meant to leave a trail which can also attract other members of the group to find the sites.
   In addition to social cues on finding places to eat, animals can also socially learn what to eat. Visual cues play a very important role in members of the same species.  It has been found in this research that domesticated chicks observing a mechanized-arrow peck at certain colored pinheads will also favor those colored pinheads.  Similarly when red-winged blackbirds or the Burmese fowl watch members of their species eating certain types of foods, they immediately prefer those types of foods as well.  It is much more difficult, however, for species to convey food taste-aversions to other members of the species.  A surprising finding was reported that when a Norway rat saw another member of its species eat a food and become sick, it still showed a preference for that food, rather than an aversion to it.  Comparing to humans, it must be something about the more advanced mind that can decipher what constitutes illness and taste preference, because humans usually avoid a food that they see is making their fellow humans sick.  It is rare, however, to find socially learned taste-aversion in most non-humans, even primates.
    Finally, animals also learn their behaviors of how to eat through social observation.  Black rats that feed on pine seeds from pine cones learn how to break open the cones by observing members of their species.  It is worth noting that multiple lineages and hundreds of different species all learn through similar mechanisms, lending credence to the fact that learning through observation has been around for tens to hundreds of thousands of years.  From early development, infants are unable to forage for themselves, therefore, it would only make sense that they acquire the skills necessary to find food and how to eat them through observation and imitation of the older members of their group.
    The authors of the paper mention that imitation is a "type of learning specialized for exploitation of public information, [which remains] both tentative and largely restricted to apes".  I wonder why this is the case, as they never clarify how what rats and birds do is not imitation, but are simply called observation and social learning.  The example they have given in the text is milk-bottle opening by apes which is a form of learning by imitation. Essentially most types of learning involves some type of observation, internalization and imitation, but this might be about how one defines true "imitation".
    There is no doubt that social behavior plays a large role in learning in a vast array of species.  Ranging from sounds and chemicals alerting others to the location of food, to the types of food and places to find them, animals are constantly interacting with other members of their species.  It is always important to keep things in an evolutionary perspective, as it would be most beneficial to a species for other members to survive as well and pass on their genes.  In a sense it is a type of kin selection, since all members of a species are related in one way or another through a common ancestor, and they are essentially looking out for "one of their own" by providing some of their extra food to others.  There could be the possibility of a reciprocity of the good deed, but in general, favors are doled out for the success of the species as a whole.
   This article was quite lengthy and informative, so I will continue writing about its various topics in the next post.  Stay tuned!


Galef, B. G., Jr, & Giraldeau, L.-A.  (2001).  Social influences on foraging in vertebrates: causal mechanisms and adaptive functions. Animal Behaviour, 61(1), 3-15.