Behavioral Development

Okay--so adult ground squirrels have three different kinds of calls they use that appear to refer to different kinds of predators, and adult ground squirrels behave differently depending on what kind of alarm call they hear.

It turns out that young ground squirrels do NOT behave like adults do when a snake is sighted. A very young ground squirrel will sometimes make the "rattlesnake" call if it sees a very big snake, even if that snake is a gopher snake.

Those who hold the first set of assumptions would say that the baby's behavior is different simply because it does not know any better yet. It has made a mistake; nothing more.

Can you think of some data you could collect that would support such a view of why the ground squirrel pup's behavior is different from the adults'?

What should adults do when they hear a young ground squirrel making the call for "rattlesnake," if those with this first point of view are correct?

That's right--the adults should ignore "rattlesnake" calls made by young squirrels, since in all likelihood the youngsters are mistaken.

However, what about the other point of view? This point of view would say that when young ground squirrels make the "rattlesnake" call to any big snake, they are NOT making a mistake. Rather, they are behaving appropriately for their own particular ecological niche. To a very young ground squirrel, ANY big snake is a VERY bad snake. By making the alarm call associated with the worst kind of snake predators, these young animals are assuring they will get rapid and aggressive help.

What should adults do when they hear a young ground squirrel making the call for "rattlesnake" if those with THIS pint of view are correct?

That's right--the adults should come running. They should NOT treat calls from youngsters as "mistakes" but should behave in a way that suggests they take these calls seriously.

Which view is right? Remember, these "views" are basically theories about why baby animals do not behave like adults. Which one best explains a particular behavior will depend on the data that can be collected to support that point of view.

One way to do this is to look at the processes that appear to contribute to that development. Let's return to our young white-crowned sparrow male for more on this topic.

Remember that the young white-crowned sparrow male does not begin to sing his own species-typical adult male song until he is some 200-days old. How does that song develop?

This question has been addressed by rearing some hatchling white-crowned sparrow males in isolation, so that they do not have the opportunity to hear other conspecific males.

A young white-crowned sparrow male reared without the opportunity to hear its own father or some other conspecific male sing will NEVER grow up to sing the species-typical song. It will sing SOME kind of song. But that song will not be recognizable as white-crowned sparrow song.

However, a hatchling sparrow that is played some tapes of male white-crowned sparrow songs when he is between the ages of 10 and 50 days of age WILL learn to sing the species-typical adult song. This is most remarkable, since the youngster will not even begin practicing any kind of song until he is 100 days old or so. That means he must remember the song he heard when very young somehow, and then work to reproduce it when he begins to sing for himself.

Could we get our young males reared in isolation to sing ANY kind of song? Nope. If you play tapes of swamp sparrow song to young isolate white-crowned sparrow males, they will grow up to sing the same dysfunctional song they would have if they never heard ANY bird when they were young. So the ability to remember hearing a given song and then recreate it later when an adult is limited to hearing adult white-crowned sparrow song.

We CAN get our young males to sing a different song when adults, however, if we REAR them with nonconspecifics. Young male white-crowned sparrows that are foster-reared by swamp sparrow parents WILL learn to sing the song of the swamp sparrow when they are adults. It appears that hearing the song of a nonconspecific is not enough, but hearing that song AND getting to interact with the nonconspecific will result in getting our young male to sing what is essentially the "wrong" song when he is an adult.

Sound complicated? Wait--there is more! It turns out our little guy also has to be able to hear himself practice during the babbling phase of his "language development." If we deafen him before that, no matter what kind of tapes he got to hear before we deafened him, he will not learn to sing the species-typical song.

Normal adult male song development in white-crowned sparrow males, then, appears to be a delicate interplay of both "nature" (he appears to have some "built-in" templates that allow him to be maximally sensitive to the "right" song when he hears it), AND "nurture" (he has to hear himself practice, and cannot learn a nonconspecific song unless he has actual social experience with that species).

What about the cowbird? Cowbirds are parasitic brooders, laying their eggs in the nests of other birds and never raising their own offspring. So a young male cowbird rarely hears his dad's song when he is growing up. He is always in a kind of natural "isolation" experiment.

As you might guess, male cowbird song development then must be largely a consequence of "nature;" it must be mostly "built-in" or inherited.

It turns out to be not so simple. Meredith West raised some male cowbirds in isolation from other cowbirds, so that they did not even have a chance to interact with other cowbirds once they fledged and were "teenagers." Then she introduced them to an established colony of cowbirds to see what would happen.

What she observed is that isolate-reared cowbirds sang BEAUTIFUL cowbird song; it was even more perfect than the adult songs of young cowbird males that had opportunity to interact with adult cowbird males ("perfect" here is operationally defined in terms of how well the song "talked" females into copulatory postures). However, when the isolate males let loose with their perfect songs in the cowbird colony, the adult males in the colony attacked them. The young males who had opportunities to interact with adult males sang less perfect songs, but did not get attacked. It appears that the "final" kind of song a young male cowbird sings is not only a function of "nature" (i.e, the fact that he is a cowbird), but also a function of "nurture" (specifically, his experience with other territorial males).

But females have a role in it too. Male cowbirds will also modify their song in reaction to how a female responds to it. A male cowbird then has a bit of a problem when trying to perfect his adult song. He needs to have a song that attracts females, but that is not SO attractive to females that it elicits attacks from other males. Even in cowbirds, then, adult male song development depends on an interaction of nature and nuture.

One more example: How does temperament develop in rats?

To study this question, Dennenberg and Whimbey did a study in the 1960's in which they bred some female rats, and then assigned these rats to one of two groups. The experimental group was handled every day during their pregnancies. Handling consisted of picking up the female, moving her to a novel cage for a few minutes, then moving her back.

The control group was not handled.

When the rats delivered, Denneberg and Whimbey allowed the pups to grow up and then tested them for a temperament quality ("emotionality," or how emotional the animals were in response to a novel situation). They did so by placing the youngsters in a testing situation called an "open field." The open field is a gridded open arena in which one can measure fearfulness in rats by recording the number of grid sections they enter. A very fearful animal will freeze (as we do when we say we are "scared stiff"). A very fearful or emotional animal will also defecate and urinate more in the open field (another thing that also happens to humans when they are VERY frightened).

What Dennenberg and Whimbey found was that the offspring of the experimental rats were MUCH more fearful in the open field. They crossed fewer gridlines and entered fewer grid sections, while they urinated and defecated more. Thus, something that their MOTHERS experienced when pregnant had a long-lasting and profound effect on the youngsters when they were adults.

Even more amazing, Dennenberg later bred these young rats and tested THEIR offspring (the grandchildren of the original mothers in the study). Once again, the effect was obtained, with the addition that there was now a sex difference. The female grandchildren of the experiemental rats were more emotional in the open field than were the male grandchildren of the experimental rats. Both males and female grandchildren, however, showed the effect of what had happened to their grandmother during her pregnancy.

Thus Dennenberg showed what looked like a transgenerational change ("nature?") brought about by an experiential ("nurture?") difference in the P1 generation.


PSY/BIO 226: Comparative Animal Behavior
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Behavioral Development
	A female white-crowned sparrow lays some eggs. She and her mate tend them, and in a few weeks, they hatch.
	At first, the young sparrows are almost totally helpless. They have few feathers, and cannot keep themselves warm. They cannot stand on their legs, and have little control over their bodies. They cannot fly, and although they can make begging noises by which to entice their parents to feed them, they do not sing.
	About a hundred days later, the male chicks in the nest begin a kind of babbling, not unlike the babbling that very young human infants do. Their baby babblings do not sound or look like adult male white-crowned sparrow songs. But they will be very important to the young males' ability to develop a normal adult song later on.
	Finally, about 200 days after hatching, the young males are singing species-typical adult male song, and using that song both to hold territories of their own and to win females. You can listen to some white crowned sparrow song here. To read more about sparrow song development, and hear some additional songs, click here (you will need Real Audio Player to hear these songs. It can be downloaded for free here.)
The question remains: How did the young males' behavior change? What explains why their behavior was so different when they were hatchlings, versus when they were "teenage" birds, versus when they were adults? Why is the behavior of babies different from that of adults?

I. "World Views" Re: Developing Animals As with many topics in the study of animal behavior, there are several opinions on how best to explain the differences between babies and adults in terms of how they behave. One point of view has as its foundation the assumption that young animals are basically little more than "incomplete" or "unfinished" adults. From this point of view, babies behave differently than do adults because they simply "aren't there yet." Once they are old enough, they will stop behaving inappropriately and show the adult behavior expected of that species. Another point of view on this question argues quite the opposite. Animal behaviorists arguing from this point of view assume that baby animals behave differently than adults do because their needs and indeed their whole "ecology" (if you will) is different from those of adults. Of course they behave differently! But that does not mean they are not behaving appropriately. Let's look at an example of some infant behavior that differs from the behavior of adults, so we can see how these two different points of view would explain that difference.
	The California ground squirrel lives in burrows in open grassland areas all over the foothills and valleys of California.
The ground squirrels live in extensive colonies called "coteries." Each cotery consists primarily of related females and their young, with a few breeding males. Young males emigrate from their coteries when they become sexually mature, while young females stay in the home cotery. Adult ground squirrels make extensive use of calls to defend their cotery and communicate with one another. For example, they have specific alarm calls for each of the major types of predators that pursue them.
	Coyotes, dogs, cats, and other terrestrial mammals (including humans) make up one such class of predators. When a ground squirrel sees one of these kinds of predators approaching the cotery, she emits a particular kind of call. Every ground squirrel in the vicinity that hears this call immediately runs to a burrow entrance, then waits and looks around. After all, if the terrestrial predator trots on past, one can quickly go back to feeding above ground. However, if it looks like danger is approaching, one can also easily dive into the burrow to safety. Terrestrial predators are fast, but not that fast.
	Another ground squirrel predator comes in the form of hawks and other birds of prey. These are VERY fast predators, and when a ground squirrel sees one, it again has a very special call that seems to mean "aerial predator!" When other ground squirrels hear this call, they immediately dive for the nearest burrow. They do not pause at the entrance to "check it out." Aerial predators are too fast to allow this chancy behavior.
	The third type of predator a ground squirrel has is the snake. In particular, two kinds of snakes make meals out of ground squirrels in California. One of these is the gopher snake shown here. The gopher snake is a constrictor, killing its prey by crushing. It can look rather like a rattle snake in color, but it does not have venom. Ground squirrels have yet another call that means "snake!" When this call is heard, a ground squirrel immediately stands up or sits up on its back legs and looks around. If it can see the snake, it will head over to it and begin to jump at it, bite at it, and kick sand in its face, in what looks like an attempt to drive the snake out of the cotery. If you think about it, this makes sense. After all, the young squirrel pups are down in the burrows, and a snake can easily slide into a burrow (unlike hawks or coyotes!) Better to get the snake the heck out of there, if you can!
	Even more interesting, ground squirrels that have evolved in areas where there are rattlesnakes have two different kinds of snake calls. One appears to mean "snake!" and is used when a gopher or other similar snake is sighted. The other appears to mean "rattlesnake" and is used only when rattlesnakes are sighted. The rattlesnake call elicits even more defensive behaviors on the part of the squirrels, as they join together to try to drive the snake away.
Okay--so adult ground squirrels have three different kinds of calls they use that appear to refer to different kinds of predators, and adult ground squirrels behave differently depending on what kind of alarm call they hear. What does this have to do with behavioral development? It turns out that young ground squirrels do NOT behave like adults do when a snake is sighted. A very young ground squirrel will sometimes make the "rattlesnake" call if it sees a very big snake, even if that snake is a gopher snake. The question again is why is the baby's behavior different from the adult's? Those who hold the first set of assumptions would say that the baby's behavior is different simply because it does not know any better yet. It has made a mistake; nothing more. Can you think of some data you could collect that would support such a view of why the ground squirrel pup's behavior is different from the adults'? What should adults do when they hear a young ground squirrel making the call for "rattlesnake," if those with this first point of view are correct? That's right--the adults should ignore "rattlesnake" calls made by young squirrels, since in all likelihood the youngsters are mistaken. However, what about the other point of view? This point of view would say that when young ground squirrels make the "rattlesnake" call to any big snake, they are NOT making a mistake. Rather, they are behaving appropriately for their own particular ecological niche. To a very young ground squirrel, ANY big snake is a VERY bad snake. By making the alarm call associated with the worst kind of snake predators, these young animals are assuring they will get rapid and aggressive help. What should adults do when they hear a young ground squirrel making the call for "rattlesnake" if those with THIS pint of view are correct? That's right--the adults should come running. They should NOT treat calls from youngsters as "mistakes" but should behave in a way that suggests they take these calls seriously. Which view is right? Remember, these "views" are basically theories about why baby animals do not behave like adults. Which one best explains a particular behavior will depend on the data that can be collected to support that point of view. II. How Do We Study Development? One way to do this is to look at the processes that appear to contribute to that development. Let's return to our young white-crowned sparrow male for more on this topic. Remember that the young white-crowned sparrow male does not begin to sing his own species-typical adult male song until he is some 200-days old. How does that song develop? This question has been addressed by rearing some hatchling white-crowned sparrow males in isolation, so that they do not have the opportunity to hear other conspecific males. A young white-crowned sparrow male reared without the opportunity to hear its own father or some other conspecific male sing will NEVER grow up to sing the species-typical song. It will sing SOME kind of song. But that song will not be recognizable as white-crowned sparrow song. However, a hatchling sparrow that is played some tapes of male white-crowned sparrow songs when he is between the ages of 10 and 50 days of age WILL learn to sing the species-typical adult song. This is most remarkable, since the youngster will not even begin practicing any kind of song until he is 100 days old or so. That means he must remember the song he heard when very young somehow, and then work to reproduce it when he begins to sing for himself. Could we get our young males reared in isolation to sing ANY kind of song? Nope. If you play tapes of swamp sparrow song to young isolate white-crowned sparrow males, they will grow up to sing the same dysfunctional song they would have if they never heard ANY bird when they were young. So the ability to remember hearing a given song and then recreate it later when an adult is limited to hearing adult white-crowned sparrow song. We CAN get our young males to sing a different song when adults, however, if we REAR them with nonconspecifics. Young male white-crowned sparrows that are foster-reared by swamp sparrow parents WILL learn to sing the song of the swamp sparrow when they are adults. It appears that hearing the song of a nonconspecific is not enough, but hearing that song AND getting to interact with the nonconspecific will result in getting our young male to sing what is essentially the "wrong" song when he is an adult. Sound complicated? Wait--there is more! It turns out our little guy also has to be able to hear himself practice during the babbling phase of his "language development." If we deafen him before that, no matter what kind of tapes he got to hear before we deafened him, he will not learn to sing the species-typical song. Normal adult male song development in white-crowned sparrow males, then, appears to be a delicate interplay of both "nature" (he appears to have some "built-in" templates that allow him to be maximally sensitive to the "right" song when he hears it), AND "nurture" (he has to hear himself practice, and cannot learn a nonconspecific song unless he has actual social experience with that species). What about the cowbird? Cowbirds are parasitic brooders, laying their eggs in the nests of other birds and never raising their own offspring. So a young male cowbird rarely hears his dad's song when he is growing up. He is always in a kind of natural "isolation" experiment. As you might guess, male cowbird song development then must be largely a consequence of "nature;" it must be mostly "built-in" or inherited. It turns out to be not so simple. Meredith West raised some male cowbirds in isolation from other cowbirds, so that they did not even have a chance to interact with other cowbirds once they fledged and were "teenagers." Then she introduced them to an established colony of cowbirds to see what would happen. What she observed is that isolate-reared cowbirds sang BEAUTIFUL cowbird song; it was even more perfect than the adult songs of young cowbird males that had opportunity to interact with adult cowbird males ("perfect" here is operationally defined in terms of how well the song "talked" females into copulatory postures). However, when the isolate males let loose with their perfect songs in the cowbird colony, the adult males in the colony attacked them. The young males who had opportunities to interact with adult males sang less perfect songs, but did not get attacked. It appears that the "final" kind of song a young male cowbird sings is not only a function of "nature" (i.e, the fact that he is a cowbird), but also a function of "nurture" (specifically, his experience with other territorial males). But females have a role in it too. Male cowbirds will also modify their song in reaction to how a female responds to it. A male cowbird then has a bit of a problem when trying to perfect his adult song. He needs to have a song that attracts females, but that is not SO attractive to females that it elicits attacks from other males. Even in cowbirds, then, adult male song development depends on an interaction of nature and nuture. One more example: How does temperament develop in rats? To study this question, Dennenberg and Whimbey did a study in the 1960's in which they bred some female rats, and then assigned these rats to one of two groups. The experimental group was handled every day during their pregnancies. Handling consisted of picking up the female, moving her to a novel cage for a few minutes, then moving her back. The control group was not handled. When the rats delivered, Denneberg and Whimbey allowed the pups to grow up and then tested them for a temperament quality ("emotionality," or how emotional the animals were in response to a novel situation). They did so by placing the youngsters in a testing situation called an "open field." The open field is a gridded open arena in which one can measure fearfulness in rats by recording the number of grid sections they enter. A very fearful animal will freeze (as we do when we say we are "scared stiff"). A very fearful or emotional animal will also defecate and urinate more in the open field (another thing that also happens to humans when they are VERY frightened). What Dennenberg and Whimbey found was that the offspring of the experimental rats were MUCH more fearful in the open field. They crossed fewer gridlines and entered fewer grid sections, while they urinated and defecated more. Thus, something that their MOTHERS experienced when pregnant had a long-lasting and profound effect on the youngsters when they were adults. Even more amazing, Dennenberg later bred these young rats and tested THEIR offspring (the grandchildren of the original mothers in the study). Once again, the effect was obtained, with the addition that there was now a sex difference. The female grandchildren of the experiemental rats were more emotional in the open field than were the male grandchildren of the experimental rats. Both males and female grandchildren, however, showed the effect of what had happened to their grandmother during her pregnancy. Thus Dennenberg showed what looked like a transgenerational change ("nature?") brought about by an experiential ("nurture?") difference in the P1 generation.