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533
26Animal Behavior
Concept Outline
26.1 Ethology focuses on the natural history ofbehavior.
Approaches to the Study of Behavior. Field biologistsfocus on
evolutionary aspects of behavior.Behavioral Genetics. At least some
behaviors aregenetically determined.
26.2 Comparative psychology focuses on how learninginfluences
behavior.
Learning. Association plays a major role in learning.The
Development of Behavior. Parent-offspringinteractions play a key
role in the development of behavior.The Physiology of Behavior.
Hormones influence manybehaviors, particularly reproductive
ones.Behavioral Rhythms. Many behaviors are governed byinnate
biological clocks.
26.3 Communication is a key element of many animalbehaviors.
Courtship. Animals use many kinds of signals to courtone
another.Communication in Social Groups. Bees and other
socialanimals communicate in complex ways.
26.4 Migratory behavior presents many puzzles.
Orientation and Migration. Animals use many cuesfrom the
environment to navigate during migrations.
26.5 To what degree animals think is a subject oflively
dispute.
Animal Cognition. It is not clear to what degree
animalsthink.
Organisms interact with their environment in manyways. To
understand these interactions, we need toappreciate both the
internal factors that shape the way ananimal behaves, as well as
aspects of the external environ-ment that affect individuals and
organisms. In this chapter,we explore the mechanisms that determine
an animals be-havior (figure 26.1), as well as the ways in which
behaviordevelops in an individual. In the next chapter, we will
con-sider the field of behavioral ecology, which investigateshow
natural selection has molded behavior through evolu-tionary
time.
FIGURE 26.1Rearing offspring involves complex behaviors. Living
in groupscalled prides makes lions better mothers. Females share
theresponsibilities of nursing and protecting the prides
young,increasing the probability that the youngsters will survive
intoadulthood.
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other males and to attract a female to reproduce; this isthe
ultimate, or evolutionary, explanation for the
malesvocalization.
The study of behavior has had a long history of contro-versy.
One source of controversy has been the question ofwhether behavior
is determined more by an individualsgenes or its learning and
experience. In other words, is be-havior the result of nature
(instinct) or nurture (experi-ence)? In the past, this question has
been considered an ei-ther/or proposition, but we now know that
instinct andexperience both play significant roles, often
interacting incomplex ways to produce the final behavior. The
scientificstudy of instinct and learning, as well as their
interrelation-ship, has led to the growth of several scientific
disciplines,including ethology, behavioral genetics, behavioral
neuro-science, and comparative psychology.
Ethology
Ethology is the study of the natural history of behavior.Early
ethologists (figure 26.2) were trained in zoology andevolutionary
biology, fields that emphasize the study of an-imal behavior under
natural conditions. As a result of thistraining, they believed that
behavior is largely instinctive,or innatethe product of natural
selection. Because behav-ior is often stereotyped (appearing in the
same way in dif-ferent individuals of a species), they argued that
it must bebased on preset paths in the nervous system. In their
view,these paths are structured from genetic blueprints andcause
animals to show a relatively complete behavior thefirst time it is
produced.
The early ethologists based their opinions on behav-iors such as
egg retrieval by geese. Geese incubate theireggs in a nest. If a
goose notices that an egg has beenknocked out of the nest, it will
extend its neck toward theegg, get up, and roll the egg back into
the nest with aside-to-side motion of its neck while the egg is
tuckedbeneath its bill. Even if the egg is removed during
re-trieval, the goose completes the behavior, as if driven bya
program released by the initial sight of the egg outsidethe nest.
According to ethologists, egg retrieval behavioris triggered by a
sign stimulus (also called a key stimu-lus), the appearance of an
egg out of the nest; a compo-nent of the gooses nervous system, the
innate releasingmechanism, provides the neural instructions for
themotor program, or fixed action pattern (figure 26.3).More
generally, the sign stimulus is a signal in the en-vironment that
triggers a behavior. The innate releasingmechanism is the sensory
mechanism that detects the sig-nal, and the fixed action pattern is
the stereotyped act.
534 Part VII Ecology and Behavior
Approaches to the Study of BehaviorDuring the past two decades,
the study of animal behaviorhas emerged as an important and diverse
science thatbridges several disciplines within biology. Evolution,
ecol-ogy, physiology, genetics, and psychology all have naturaland
logical linkages with the study of behavior, each disci-pline
adding a different perspective and addressing differ-ent
questions.
Research in animal behavior has made major contribu-tions to our
understanding of nervous system organization,child development, and
human communication, as well asthe process of speciation, community
organization, and themechanism of natural selection itself. The
study of the be-havior of nonhuman animals has led to the
identification ofgeneral principles of behavior, which have been
applied,often controversially, to humans. This has changed the
waywe think about the origins of human behavior and the waywe
perceive ourselves.
Behavior can be defined as the way an organism re-sponds to
stimuli in its environment. These stimuli mightbe as simple as the
odor of food. In this sense, a bacterialcell behaves by moving
toward higher concentrations ofsugar. This behavior is very simple
and well-suited to thelife of bacteria, allowing these organisms to
live and repro-duce. As animals evolved, they occupied different
environ-ments and faced diverse problems that affected their
sur-vival and reproduction. Their nervous systems andbehavior
concomitantly became more complex. Nervoussystems perceive and
process information concerning envi-ronmental stimuli and trigger
adaptive motor responses,which we see as patterns of behavior.
When we observe animal behavior, we can explain it intwo
different ways. First, we might ask how it all works,that is, how
the animals senses, nerve networks, or inter-nal state provide a
physiological basis for the behavior. Inthis way, we would be
asking a question of proximatecausation. To analyze the proximate
cause of behavior,we might measure hormone levels or record the
impulseactivity of neurons in the animal. We could also ask whythe
behavior evolved, that is, what is its adaptive value?This is a
question concerning ultimate causation. Tostudy the ultimate cause
of a behavior, we would attemptto determine how it influenced the
animals survival or re-productive success. Thus, a male songbird
may sing dur-ing the breeding season because it has a level of
thesteroid sex hormone, testosterone, which binds to hor-mone
receptors in the brain and triggers the productionof song; this
would be the proximate cause of the malebirds song. But the male
sings to defend a territory from
26.1 Ethology focuses on the natural history of behavior.
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Similarly, a frog unfolds its long, sticky tongue at thesight of
a moving insect, and a male stickleback fish willattack another
male showing a bright red underside. Suchresponses certainly appear
to be programmed and in-stinctive, but what evidence supports the
ethological viewthat behavior has an underlying neural basis?
Behavior as a Response to Stimuli in theEnvironment
In the example of egg retrieval behavior in geese, a goosemust
first perceive that an egg is outside of the nest. To re-spond to
this stimulus, it must convert one form of energywhich is an input
to its visual systemthe energy of pho-tons of lightinto a form of
energy its nervous system canunderstand and use to respondthe
electrical energy of anerve impulse. Animals need to respond to
other stimuli inthe environment as well. For an animal to orient
from afood source back to its nest, it might rely on the position
ofthe sun. To find a mate, an animal might use a particularchemical
scent. The electromagnetic energy of light andthe chemical energy
of an odor must be converted to theelectrical energy of a nerve
impulse. This is done throughtransduction, the conversion of energy
in the environmentto an action potential, and the first step in the
processing ofstimuli perceived by the senses. For example,
rhodopsin isresponsible for the transduction of visual
stimuli.Rhodopsin is made of cis-retinal and the protein
opsin.Light is absorbed by the visual pigment cis-retinal causing
it
to change its shape to trans-retinal (see chapter 55). This
inturn changes the shape of the companion protein opsin,and induces
the first step in a cascade of molecular eventsthat finally
triggers a nerve impulse. Sound, odor, andtastes are transduced to
nerve impulses by similarprocesses.
Ethologists study behavior from an evolutionaryperspective,
focusing on the neural basis of behaviors.
Chapter 26 Animal Behavior 535
FIGURE 26.2The founding fathers of ethology: Karl von Frisch,
Konrad Lorenz, and Niko Tinbergen pioneered the study of
behavioralscience. In 1973, they received the Nobel Prize in
Physiology or Medicine for their path-making contributions. Von
Frisch led the studyof honeybee communication and sensory biology.
Lorenz focused on social development (imprinting) and the natural
history ofaggression. Tinbergen examined the functional
significance of behavior and was the first behavioral
ecologist.
FIGURE 26.3Lizard prey capture. The complex series of movements
of thetongue this chameleon uses to capture an insect represents a
fixedaction pattern.
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Behavioral GeneticsIn a famous experiment carried out in the
1940s, RobertTryon studied the ability of rats to find their way
througha maze with many blind alleys and only one exit, where
areward of food awaited. Some rats quickly learned to zipright
through the maze to the food, making few incorrectturns, while
other rats took much longer to learn the cor-rect path (figure
26.4). Tryon bred the fast learners withone another to establish a
maze-bright colony, and hesimilarly bred the slow learners with one
another to estab-lish a maze-dull colony. He then tested the
offspring ineach colony to see how quickly they learned the
maze.The offspring of maze-bright rats learned even morequickly
than their parents had, while the offspring ofmaze-dull parents
were even poorer at maze learning.After repeating this procedure
over several generations,Tryon was able to produce two behaviorally
distinct typesof rat with very different maze-learning abilities.
Clearlythe ability to learn the maze was to some degree
heredi-tary, governed by genes passed from parent to
offspring.Furthermore, those genes were specific to this
behavior,as the two groups of rats did not differ in their ability
toperform other behavioral tasks, such as running a com-pletely
different kind of maze. Tryons research demon-strates how a study
can reveal that behavior has a herita-ble component.
Further support for the genetic basis of behavior hascome from
studies of hybrids. William Dilger of CornellUniversity has
examined two species of lovebird (genusAgapornis), which differ in
the way they carry twigs, paper,and other materials used to build a
nest. A. personata holdsnest material in its beak, while A.
roseicollis carries materialtucked under its flank feathers (figure
26.5). When Dilgercrossed the two species to produce hybrids, he
found thatthe hybrids carry nest material in a way that seems
inter-mediate between that of the parents: they repeatedly
shiftmaterial between the bill and the flank feathers. Otherstudies
conducted on courtship songs in crickets and treefrogs also
demonstrate the intermediate nature of hybridbehavior.
The role of genetics can also be seen in humans bycomparing the
behavior of identical twins. Identical twinsare, as their name
implies, genetically identical. How-ever, most sets of identical
twins are raised in the sameenvironment, so it is not possible to
determine whethersimilarities in behavior result from their genetic
similar-ity or from experiences shared as they grew up (the
clas-sic nature versus nurture debate). However, in somecases,
twins have been separated at birth. A recent studyof 50 such sets
of twins revealed many similarities in per-sonality, temperament,
and even leisure-time activities,even though the twins were often
raised in very differentenvironments. These similarities indicate
that geneticsplays a role in determining behavior even in humans,
al-though the relative importance of genetics versus envi-ronment
is still hotly debated.
536 Part VII Ecology and Behavior
Parentalgeneration
Firstgeneration
Secondgeneration
Fifthgeneration
Seventhgeneration
Total number of errors innegotiating the maze
(fourteen trials)
9 39 64 114 214Quicker ratsSlower rats
FIGURE 26.4The genetics of learning. Tryon selected rats for
their ability tolearn to run a maze and demonstrated that this
ability isinfluenced by genes. He tested a large group of rats,
selectedthose that ran the maze in the shortest time, and let them
breedwith one another. He then tested their progeny and again
selectedthose with the quickest maze-running times for breeding.
Afterseven generations, he had succeeded in halving the average
timean inexperienced rat required to negotiate the maze.
Parallelartificial selection for slow running time more than
doubled theaverage running time.
FIGURE 26.5Genetics of lovebird behavior. Lovebirds inherit the
tendency tocarry nest material, such as these paper strips, under
their flankfeathers.
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Single Gene Effects on Behavior
The maze-learning, hybrid, and identical twins studies
justdescribed suggest genes play a role in behavior, but
recentresearch has provided much greater detail on the geneticbasis
of behavior. In the fruit fly Drosophila, and in mice,many
mutations have been associated with particular be-havioral
abnormalities.
In fruit flies, for example, individuals that possess
alter-native alleles for a single gene differ greatly in their
feedingbehavior as larvae; larvae with one allele move around
agreat deal as they eat, whereas individuals with the alterna-tive
allele move hardly at all. A wide variety of mutations atother
genes are now known in Drosophila which affect al-most every aspect
of courtship behavior.
The ways in which genetic differences affect behaviorhave been
worked out for several mouse genes. For example,some mice with one
mutation have trouble remembering in-formation that they learned
two days earlier about where ob-jects are located. This difference
appears to result becausethe mutant mice do not produce the enzyme
-calcium-calmodulin-dependent kinase II, which plays an
importantrole in the functioning of a part of the brain, the
hippocam-pus, that is important for spatial learning.
Modern molecular biology techniques allow the role ofgenetics in
behavior to be investigated with ever greaterprecision. For
example, male mice genetically engineered(as knock-outs) to lack
the ability to synthesize nitricoxide, a brain neurotransmitter,
show increased aggressivebehavior.
A particularly fascinating breakthrough occurred in1996, when
scientists using the knock-out technique dis-covered a new gene,
fosB, that seems to determine whetheror not female mice will
nurture their young. Females withboth fosB alleles knocked out will
initially investigate theirnewborn babies, but then ignore them, in
stark contrast tothe caring and protective maternal behavior
provided bynormal females (figure 26.6).
The cause of this inattentiveness appears to result from achain
reaction. When mothers of new babies initially in-spect them,
information from their auditory, olfactory, andtactile senses are
transmitted to the hypothalamus, wherefosB alleles are activated,
producing a particular protein,which in turn activates other
enzymes and genes that affectthe neural circuitry within the
hypothalamus. These modi-fications within the brain cause the
female to react mater-nally toward her offspring. In contrast, in
mothers lackingthe fosB alleles, this reaction is stopped midway.
No proteinis activated, the brains neural circuitry is not rewired,
andmaternal behavior does not result.
As these genetic techniques are becoming used morewidely, the
next few years should see similar dramatic ad-vances in our
knowledge of how genes affect behavior inmany varieties of
humans.
The genetic basis of behavior is supported by
artificialselection experiments, hybridization studies, andstudies
on the behavior of mutants. Research has alsoidentified specific
genes that control behavior.
Chapter 26 Animal Behavior 537
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1.0
0.8
0.6
0.4
0.2
(c)
(d)fosB alleles present
fosB alleles absent
Min
utes
cro
uch
ing
ove
ro
ffspr
ing
Prop
ortio
no
fpu
psre
triev
ed
(a)
(b)
FIGURE 26.6Genetically causeddefect in maternalcare. (a) In
mice,normal mothers takevery good care of theiroffspring,
retrievingthem if they moveaway and crouchingover them. (b)
Motherswith the mutant fosBallele perform neitherof these
behaviors,leaving their pupsexposed. (c) Amount oftime female mice
wereobserved crouching ina nursing posture overoffspring.(d)
Proportion of pupsretrieved when theywere experimentallymoved.
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LearningWhile ethologists were attempting to explain behavior
asan instinctive process, comparative psychologists focusedheavily
on learning as the major element that shapes behav-ior. These
behavioral scientists, working primarily on ratsin laboratory
settings, identified the ways in which animalslearn. Learning is
any modification of behavior that resultsfrom experience rather
than maturation.
The simplest type of learning, nonassociative learn-ing, does
not require an animal to form an associationbetween two stimuli or
between a stimulus and a re-sponse. One form of nonassociative
learning is habitua-tion, which can be defined as a decrease in
response to arepeated stimulus that has no positive or negative
conse-quences (that is, no reinforcement). In many cases,
thestimulus evokes a strong response when it is first encoun-tered,
but the magnitude of the response gradually de-clines with repeated
exposure. For example, young birdssee many types of objects moving
overhead. At first, theymay respond by crouching down and remaining
still.Some of the objects, like falling leaves or members oftheir
own species flying by, are seen very frequently andhave no positive
or negative consequence to thenestlings. Over time, the young birds
may habituate tosuch stimuli and stop responding. Thus, habituation
canbe thought of as learning not to respond to a stimulus.Being
able to ignore unimportant stimuli is critical to ananimal
confronting a barrage of stimuli in a complex en-vironment. Another
form of nonassociative learning issensitization, characterized by
an increased responsive-ness to a stimulus. Sensitization is
essentially the oppositeof habituation.
A change in behavior that involves an association be-tween two
stimuli or between a stimulus and a response istermed associative
learning (figure 26.7). The behavioris modified, or conditioned,
through the association.This form of learning is more complex than
habituationor sensitization. The two major types of associative
learn-ing are called classical conditioning and operant
con-ditioning; they differ in the way the associations
areestablished.
Classical Conditioning
In classical conditioning, the paired presentation of
twodifferent kinds of stimuli causes the animal to form an
asso-ciation between the stimuli. Classical conditioning is
alsocalled Pavlovian conditioning, after Russian psychologistIvan
Pavlov, who first described it. Pavlov presented meatpowder, an
unconditioned stimulus, to a dog and noted thatthe dog responded by
salivating, an unconditioned response. Ifan unrelated stimulus,
such as the ringing of a bell, was
538 Part VII Ecology and Behavior
26.2 Comparative psychology focuses on how learning influences
behavior.
FIGURE 26.7Learning what is edible. Associative learning is
involved inpredator-prey interactions. (a) A naive toad is offered
abumblebee as food. (b) The toad is stung, and (c)
subsequentlyavoids feeding on bumblebees or any other insects
having theirblack-and-yellow coloration. The toad has associated
theappearance of the insect with pain, and modifies its
behavior.
(a)
(b)
(c)
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presented at the same time as the meat powder, over re-peated
trials the dog would salivate in response to thesound of the bell
alone. The dog had learned to associatethe unrelated sound stimulus
with the meat powder stimu-lus. Its response to the sound stimulus
was, therefore, con-ditioned, and the sound of the bell is referred
to as a condi-tioned stimulus.
Operant Conditioning
In operant conditioning, an animal learns to associate
itsbehavioral response with a reward or punishment. Ameri-can
psychologist B. F. Skinner studied operant condition-ing in rats by
placing them in an apparatus that came to becalled a Skinner box.
As the rat explored the box, itwould occasionally press a lever by
accident, causing a pel-let of food to appear. At first, the rat
would ignore thelever, eat the food pellet, and continue to move
about.Soon, however, it learned to associate pressing the lever(the
behavioral response) with obtaining food (the reward).When it was
hungry, it would spend all its time pressingthe lever. This sort of
trial-and-error learning is of majorimportance to most
vertebrates.
Comparative psychologists used to believe that any twostimuli
could be linked in classical conditioning and thatanimals could be
conditioned to perform any learnablebehavior in response to any
stimulus by operant condi-tioning. As you will see below, this view
has changed.Today, it is thought that instinct guides learning by
deter-mining what type of information can be learned
throughconditioning.
Instinct
It is now clear that some animals have innate predisposi-tions
toward forming certain associations. For example, if arat is
offered a food pellet at the same time it is exposed toX rays
(which later produces nausea), the rat will rememberthe taste of
the food pellet but not its size. Conversely, if arat is given a
food pellet at the same time an electric shockis delivered (which
immediately causes pain), the rat will re-member the size of the
pellet but not its taste. Similarly, pi-geons can learn to
associate food with colors but not withsounds; on the other hand,
they can associate danger withsounds but not with colors.
These examples of learning preparedness demon-strate that what
an animal can learn is biologically influ-encedthat is, learning is
possible only within the bound-aries set by instinct. Innate
programs have evolvedbecause they underscore adaptive responses.
Rats, whichforage at night and have a highly developed sense
ofsmell, are better able to identify dangerous food by itsodor than
by its size or color. The seed a pigeon eats mayhave a distinctive
color that the pigeon can see, but itmakes no sound the pigeon can
hear. The study of learn-
ing has expanded to include its ecological significance, sothat
we are now able to consider the evolution of learn-ing. An animals
ecology, of course, is key to understand-ing what an animal is
capable of learning. Some species ofbirds, like Clarks nutcracker,
feed on seeds. Birds storeseeds in caches they bury when seeds are
abundant so theywill have food during the winter. Thousands of
seedcaches may be buried and then later recovered. Onewould expect
the birds to have an extraordinary spatialmemory, and this is
indeed what has been found (figure26.8). Clarks nutcracker, and
other seed-hoarding birds,have an unusually large hippocampus, the
center formemory storage in the brain (see chapter 54).
Habituation and sensitization are simple forms oflearning in
which there is no association betweenstimuli and responses. In
contrast, associative learning(classical and operant conditioning)
involves theformation of an association between two stimuli
orbetween a stimulus and a response.
Chapter 26 Animal Behavior 539
FIGURE 26.8The Clarks nutcracker has an extraordinary memory.
AClarks nutcracker can remember the locations of up to 2000
seedcaches months after hiding them. After conducting
experiments,scientists have concluded that the birds use features
of thelandscape and other surrounding objects as spatial references
tomemorize the locations of the caches.
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The Development ofBehaviorBehavioral biologists now
recognizethat behavior has both genetic andlearned components, and
the schoolsof ethology and psychology are lesspolarized than they
once were. Thusfar in this chapter we have discussedthe influence
of genes and learningseparately. As we will see, these
factorsinteract during development to shapebehavior.
Parent-Offspring Interactions
As an animal matures, it may form so-cial attachments to other
individuals orform preferences that will influencebehavior later in
life. This process,called imprinting, is sometimes con-sidered a
type of learning. In filial im-printing, social attachments form
be-tween parents and offspring. Forexample, young birds of some
speciesbegin to follow their mother within afew hours after
hatching, and their fol-lowing response results in a bond be-tween
mother and young. However,the young birds initial experience
de-termines how this imprint is estab-lished. The German ethologist
Kon-rad Lorenz showed that birds will follow the first objectthey
see after hatching and direct their social behavior to-ward that
object. Lorenz raised geese from eggs, and whenhe offered himself
as a model for imprinting, the goslingstreated him as if he were
their parent, following him duti-fully (figure 26.9). Black boxes,
flashing lights, and water-ing cans can also be effective
imprinting objects (figure26.10). Imprinting occurs during a
sensitive phase, or acritical period (roughly 13 to 16 hours after
hatching ingeese), when the success of imprinting is highest.
Several studies demonstrate that the social interactionsthat
occur between parents and offspring during the criticalperiod are
key to the normal development of behavior. Thepsychologist Harry
Harlow gave orphaned rhesus monkeyinfants the opportunity to form
social attachments with twosurrogate mothers, one made of soft
cloth covering awire frame and the other made only of wire. The
infantschose to spend time with the cloth mother, even if only
thewire mother provided food, indicating that texture and tac-tile
contact, rather than providing food, may be among thekey qualities
in a mother that promote infant social attach-ment. If infants are
deprived of normal social contact, theirdevelopment is abnormal.
Greater degrees of deprivationlead to greater abnormalities in
social behavior during
childhood and adulthood. Studies on orphaned human in-fants
suggest that a constant mother figure is required fornormal growth
and psychological development.
Recent research has revealed a biological need for
thestimulation that occurs during parent-offspring
interactionsearly in life. Female rats lick their pups after birth,
and thisstimulation inhibits the release of an endorphin (see
chap-ter 56) that can block normal growth. Pups that receivenormal
tactile stimulation also have more brain receptorsfor
glucocorticoid hormones, longer-lived brain neurons,and a greater
tolerance for stress. Premature human infantswho are massaged gain
weight rapidly. These studies indi-cate that the need for normal
social interaction is based inthe brain and that touch and other
aspects of contact be-tween parents and offspring are important for
physical aswell as behavioral development.
Sexual imprinting is a process in which an individuallearns to
direct its sexual behavior at members of its ownspecies.
Cross-fostering studies, in which individuals ofone species are
raised by parents of another species, revealthat this form of
imprinting also occurs early in life. Inmost species of birds,
these studies have shown that the fos-tered bird will attempt to
mate with members of its fosterspecies when it is sexually
mature.
540 Part VII Ecology and Behavior
(a)
(b)
FIGURE 26.9An unlikely parent. The eager goslingsfollowing
Konrad Lorenz think he is theirmother. He is the first object they
sawwhen they hatched, and they have usedhim as a model for
imprinting.
FIGURE 26.10How imprinting is studied. Ducklingswill imprint on
the first object they see,even (a) a black box or (b) a white
sphere.
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Interaction between Instinct and Learning
The work of Peter Marler and his colleagues on the ac-quisition
of courtship song by white-crowned sparrowsprovides an excellent
example of the interaction betweeninstinct and learning in the
development of behavior.Courtship songs are sung by mature males
and arespecies-specific. By rearing male birds in soundproof
in-cubators provided with speakers and microphones, Marlercould
control what a bird heard as it matured and recordthe song it
produced as an adult. He found that white-crowned sparrows that
heard no song at all during devel-opment, or that heard only the
song of a different species,the song sparrow, sang a poorly
developed song as adults(figure 26.11). But birds that heard the
song of their ownspecies, or that heard the songs of both the
white-crownedsparrow and the song sparrow, sang a fully
developed,white-crowned sparrow song as adults. These results
sug-gest that these birds have a genetic template, or instinc-tive
program, that guides them to learn the appropriatesong. During a
critical period in development, the tem-plate will accept the
correct song as a model. Thus, songacquisition depends on learning,
but only the song of thecorrect species can be learned. The genetic
template forlearning is selective. However, learning plays a
prominentrole as well. If a young white-crowned sparrow is
surgi-cally deafened after it hears its species song during
thecritical period, it will also sing a poorly developed song asan
adult. Therefore, the bird must practice listening tohimself sing,
matching what he hears to the model histemplate has accepted.
Although this explanation of song development stoodunchallenged
for many years, recent research has shownthat white-crowned sparrow
males can learn anotherspecies song under certain conditions. If a
live malestrawberry finch is placed in a cage next to a young
malesparrow, the young sparrow will learn to sing the straw-berry
finchs song! This finding indicates that socialstimuli may be more
effective than a tape-recorded songin overriding the innate program
that guides song devel-opment. Furthermore, the males of some bird
specieshave no opportunity to hear the song of their ownspecies. In
such cases, it appears that the males instinc-tively know their own
species song. For example, cuck-oos are brood parasites; females
lay their eggs in the nestof another species of bird, and the young
that hatch arereared by the foster parents (figure 26.12). When
thecuckoos become adults, they sing the song of their ownspecies
rather than that of their foster parents. Becausemale brood
parasites would most likely hear the song oftheir host species
during development, it is adaptive forthem to ignore such incorrect
stimuli. They hear noadult males of their own species singing, so
no correctsong models are available. In these species, natural
selec-tion has programmed the male with a genetically
guidedsong.
Interactions that occur during sensitive phases ofimprinting are
critical to normal behavioraldevelopment. Physical contact plays an
important rolein the development of psychological well-being
andgrowth.
Chapter 26 Animal Behavior 541
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6
4
2
Freq
uenc
y(kH
z)
(a)
(b) 0.5 1.0 1.5 2.0Time (s)
FIGURE 26.11Song development in birds. (a) The sonograms of
songsproduced by male white-crowned sparrows that had been
exposedto their own species song during development are different
from(b) those of male sparrows that heard no song during rearing.
Thisdifference indicates that the genetic program itself is
insufficientto produce a normal song.
FIGURE 26.12Brood parasite. Cuckoos lay their eggs in the nests
of otherspecies of birds. Because the young cuckoos (large bird to
theright) are raised by a different species (like this meadow
pipit,smaller bird to the left), they have no opportunity to learn
thecuckoo song; the cuckoo song they later sing is innate.
-
The Physiology ofBehaviorThe early ethologists emphasis on
in-stinct sometimes overlooked the internalfactors that control
behavior. If askedwhy a male bird defends a territory andsings only
during the breeding season,they would answer that a bird singswhen
it is in the right motivational stateor mood and has the
appropriate drive.But what do these phrases mean in termsof
physiological control mechanisms?
Part of our understanding of thephysiological control of
behavior hascome from the study of reproductivebehavior. Animals
show reproductivebehaviors such as courtship only duringthe
breeding season. Research onlizards, birds, rats, and other
animalshas revealed that hormones play an im-portant role in these
behaviors. Changesin day length trigger the secretion
ofgonadotropin-releasing hormone by thehypothalamus, which
stimulates the re-lease of the gonadotropins, follicle-stimulating
hormone (FSH) andluteinizing hormone, by the anterior pi-tuitary
gland. These hormones causethe development of reproductive
tissuesto ready the animal for breeding. Thegonadotropins, in turn,
stimulate the se-cretion of the steroid sex hormones, es-trogens
and progesterone in females andtestosterone in males. The sex
hor-mones act on the brain to trigger behav-iors associated with
reproduction. Forexample, birdsong and territorial behav-ior depend
upon the level of testos-terone in the male, and the receptivityof
females to male courtship dependsupon estrogen levels.
Hormones have both organizationaland activational effects. In
the exampleof birdsong given above, estrogen in themale causes the
development of thesong system, which is composed ofneural tissue in
the forebrain and itsconnections to the spinal cord and thesyrinx
(a structure like our larynx that allows the bird tosing). Early in
a males development, the gonads produceestrogen, which stimulates
neuron growth in the brain. Inthe mature male, the testes produce
testosterone, whichactivates song. Thus, the development of the
neural sys-tems that are responsible for behavior is first
organized,then activated by hormones.
Research on the physiology of repro-ductive behavior shows that
there areimportant interactions among hor-mones, behavior, and
stimuli in both thephysical and social environments of
anindividual. Daniel Lehrmans work onreproduction in ring doves
provides anexcellent example of how these factorsinteract (figure
26.13). Male courtshipbehavior is controlled by testosteroneand
related steroid hormones. Themales behavior causes the release
ofFSH in the female, and FSH promotesthe growth of the ovarian
follicles (seechapter 59). The developing follicles re-lease
estrogens, which affect other re-productive tissues. Nest
constructionfollows after one or two days. The pres-ence of the
nest then triggers the secre-tion of progesterone in the female,
initi-ating incubation behavior after the eggis laid. Feeding
occurs once the eggshatch, and this behavior is also hormon-ally
controlled.
The research of Lehrman and hiscolleagues paved the way for many
addi-tional investigations in behavioral en-docrinology, the study
of the hormonalregulation of behavior. For example,male Anolis
lizards begin courtship aftera seasonal rise in temperature, and
themales courtship is needed to stimulatethe growth of ovarian
follicles in the fe-male. These and other studies demon-strate the
interactive effects of the phys-ical environment (for
example,temperature and day length) and the so-cial environment
(such as the presenceof a nest and the courtship display of amate)
on the hormonal condition of ananimal. Hormones are, therefore,
aproximate cause of behavior. To controlreproductive behavior, they
must be re-leased when the conditions are most fa-vorable for the
growth of young. Otherbehaviors, such as territoriality
anddominance behavior, also have hormonalcorrelates.
Hormones may interact with neuro-transmitters to alter behavior.
Estrogen affects the neuro-transmitter serotonin in female mice,
and may be in partresponsible for the mood swings experienced by
somehuman females during the menstrual cycle.
Hormones have important influences on reproductiveand social
behavior.
542 Part VII Ecology and Behavior
(1)
(2)
(3)
(4)
(5)
FIGURE 26.13Hormonal control of reproductivebehavior.
Reproduction in the ring doveinvolves a sequence of
behaviorsregulated by hormones: (1) courtshipand copulation; (2)
nest building; (3) egglaying; (4) incubation; and (5) feedingcrop
milk to the young after they hatch.
-
Behavioral RhythmsMany animals exhibit behaviors that vary at
regular inter-vals of time. Geese migrate south in the fall, birds
sing inthe early morning, bats fly at night rather than during
theday, and most humans sleep at night and are active in
thedaytime. Some behaviors are timed to occur in concertwith lunar
or tidal cycles (figure 26.14). Why do regular re-peating patterns
of behavior occur, and what determineswhen they occur? The study of
questions like these has re-vealed that rhythmic animal behaviors
are based on bothendogenous (internal) rhythms and exogenous
(external)timers.
Most studies of behavioral rhythms have focused on be-haviors
that appear to be keyed to a daily cycle, such assleeping. Rhythms
with a period of about 24 hours arecalled circadian (about a day)
rhythms. Many of thesebehaviors have a strong endogenous component,
as if theywere driven by a biological clock. Such behaviors are
saidto be free-running, continuing on a regular cycle even in
theabsence of any cues from the environment. Almost all fruitfly
pupae hatch in the early morning, for example, even ifthey are kept
in total darkness throughout their week-longdevelopment. They keep
track of time with an internalclock whose pattern is determined by
a single gene, calledthe per (for period ) gene. Different
mutations of the pergene shorten or lengthen the daily rhythm. The
per geneproduces a protein in a regular 24-hour cycle in the
brain,serving as the flys pacemaker of activity. The protein
prob-ably affects the expression of other genes that
ultimatelyregulate activity. As the per protein accumulates, it
seemsto turn off the gene. In mice, the clock gene is
responsiblefor regulating the animals daily rhythm.
Most biological clocks do not exactly match the rhythmsof the
environment. Therefore, the behavioral rhythm ofan individual
deprived of external cues gradually drifts outof phase with the
environment. Exposure to an environ-mental cue resets the
biological clock and keeps the behav-ior properly synchronized with
the environment. Light isthe most common cue for resetting
circadian rhythms.
The most obvious circadian rhythm in humans is thesleep-activity
cycle. In controlled experiments, humanshave lived for months in
underground apartments, whereall light is artificial and there are
no external cues whatso-ever indicating day length. Left to set
their own schedules,most of these people adopt daily activity
patterns (onephase of activity plus one phase of sleep) of about 25
hours,although there is considerable variation. Some
individualsexhibit 50-hour clocks, active for as long as 36 hours
duringeach period! Under normal circumstances, the day-nightcycle
resets an individuals free-running clock every day toa cycle period
of 24 hours.
What constitutes an animals biological clock? In someinsects,
the clock is thought to be located in the optic lobesof the brain,
and timekeeping appears to be based on hor-mones. In mammals,
including humans, the biological
clock lies in a specific region of the hypothalamus calledthe
suprachiasmatic nucleus (SCN). The SCN is a self-sustaining
oscillator, which means it undergoes sponta-neous, cyclical changes
in activity. This oscillatory activityhelps the SCN to act as a
pacemaker for circadian rhythms,but in order for the rhythms to be
entrained to externallight-dark cycles, the SCN must be influenced
by light. Infact, there are both direct and indirect neural
projectionsfrom the retina to the SCN.
The SCN controls circadian rhythms by regulating thesecretion of
the hormone melatonin by the pineal gland.During the daytime, the
SCN suppresses melatonin secre-tion. Consequently, more melatonin
is secreted over a 24-hour period during short days than during
long days. Vari-ations in melatonin secretion thus serve as an
indicator ofseasonal changes in day length, and these variations
partici-pate in timing the seasonal reproductive behavior of
manymammals. Disturbances in melatonin secretion may be par-tially
responsible for the jet-lag people experience whenair travel
suddenly throws their internal clocks out of regis-ter with the
day-night cycle.
Many important behavioral rhythms have cycle periodslonger than
24 hours. For example, circannual behaviorssuch as breeding,
hibernation, and migration occur on ayearly cycle. These behaviors
seem to be largely timed byhormonal and other physiological changes
keyed to ex-ogenous factors such as day length. The degree to
whichendogenous biological clocks underlie circannual rhythmsis not
known, as it is very difficult to perform constant-environment
experiments of several years duration. Themechanism of the
biological clock remains one of themost tantalizing puzzles in
biology today.
Endogenous circadian rhythms have free-running cycleperiods of
approximately 24 hours; they are entrainedto a more exact 24-hour
cycle period by environmentalcues.
Chapter 26 Animal Behavior 543
FIGURE 26.14Tidal rhythm. Oysters open their shells for feeding
when thetide is in and close them when the tide is out.
-
Much of the research in animal behavior is devoted to ana-lyzing
the nature of communication signals, determininghow they are
perceived, and identifying the ecological rolesthey play and their
evolutionary origins.
CourtshipDuring courtship, animals produce signals to
communicatewith potential mates and with other members of their
ownsex. A stimulus-response chain sometimes occurs, inwhich the
behavior of one individual in turn releases a be-havior by another
individual (figure 26.15).
Courtship Signaling
A male stickleback fish will defend the nest it builds on
thebottom of a pond or stream by attacking conspecific males(that
is, males of the same species) that approach the nest.Niko
Tinbergen studied the social releasers responsible forthis behavior
by making simple clay models. He found thata models shape and
degree of resemblance to a fish were
544 Part VII Ecology and Behavior
26.3 Communication is a key element of many animal
behaviors.
Female giveshead-up displayto male
1
Male swims zigzagto female and then leads her to nest
Male showsfemale entrance to nest
2
3 4
5
Female enters nestand spawns whilemale stimulates tail Male
enters nest
and fertilizes eggs
unimportant; any model with a red underside (like the un-derside
of a male stickleback) could release the attack be-havior.
Tinbergen also used a series of clay models todemonstrate that a
male stickleback recognizes a female byher abdomen, swollen with
eggs.
Courtship signals are often species-specific, limiting
com-munication to members of the same species and thus play-ing a
key role in reproductive isolation. The flashes of fire-flies
(which are actually beetles) are such species-specificsignals.
Females recognize conspecific males by their flashpattern (figure
26.16), and males recognize conspecific fe-males by their flash
response. This series of reciprocal re-sponses provides a
continuous check on the species iden-tity of potential mates.
Visual courtship displays sometimes have more than onecomponent.
The male Anolis lizard extends and retracts hisfleshy and often
colorful dewlap while perched on a branchin his territory (figure
26.17). The display thus involvesboth color and movement (the
extension of the dewlap aswell as a series of lizard push-ups). To
which componentof the display does the female respond? Experiments
inwhich the dewlap color is altered with ink show that color
isunimportant for some species; that is, a female can becourted
successfully by a male with an atypically coloreddewlap.
FIGURE 26.15A stimulus-response chain. Stickleback courtship
involves a sequence of behaviors leading to the fertilization of
eggs.
-
Pheromones
Chemical signals also mediate interactions between malesand
females. Pheromones, chemical messengers used forcommunication
between individuals of the same species,serve as sex attractants
among other functions in many ani-mals. Even the human egg produces
a chemical attractantto communicate with sperm! Female silk moths
(Bombyxmori) produce a sex pheromone called bombykol in a
glandassociated with the reproductive system. Neurophysiologi-cal
studies show that the males antennae contain numeroussensory
receptors specific for bombykol. These receptorsare extraordinarily
sensitive, enabling the male to respondbehaviorally to
concentrations of bombykol as low as onemolecule in 1017 molecules
of oxygen in the air!
Many insects, amphibians, and birds produce species-specific
acoustic signals to attract mates. Bullfrog males callto females by
inflating and discharging air from their vocalsacs, located beneath
the lower jaw. The female can distin-guish a conspecific males call
from the call of other frogsthat may be in the same habitat and
mating at the sametime. Male birds produce songs, complex sounds
composedof notes and phrases, to advertise their presence and to
at-tract females. In many bird species, variations in the
malessongs identify particular males in a population. In
thesespecies, the song is individually specific as well as
species-specific.
Level of Specificity
Why should different signals have different levels of
speci-ficity? The level of specificity relates to the function
ofthe signal. Many courtship signals are species-specific tohelp
animals avoid making errors in mating that wouldproduce inviable
hybrids or otherwise waste reproductiveeffort. A male birds song is
individually specific because itallows his presence (as opposed to
simply the presence ofan unidentifiable member of the species) to
be recognizedby neighboring birds. When territories are being
estab-lished, males may sing and aggressively confront neighbor-ing
conspecifics to defend their space. Aggression carriesthe risk of
injury, and it is energetically costly to sing.After territorial
borders have been established, intrusionsby neighbors are few
because the outcome of the contestshave already been determined.
Each male then knowshis neighbor by the song he sings, and also
knows thatmale does not constitute a threat because they have
alreadysettled their territorial contests. So, all birds in the
popula-tion can lower their energy costs by identifying
theirneighbors through their individualistic songs. In a
similarway, mammals mark their territories with pheromones
thatsignal individual identity, which may be encoded as ablend of a
number of chemicals. Other signals, such as themobbing and alarm
calls of birds, are anonymous, convey-ing no information about the
identity of the sender. Thesesignals may permit communication about
the presence of apredator common to several bird species.
Courtship behaviors are keyed to species-specific
visual,chemical, and acoustic signals.
Chapter 26 Animal Behavior 545
1
2
3
4
5
67
8
9
FIGURE 26.16Firefly fireworks. The bioluminescent displays of
these lampyridbeetles are species-specific and serve as behavioral
mechanisms ofreproductive isolation. Each number represents the
flash patternof a male of a different species.
FIGURE 26.17Dewlap display of a male Anolis lizard. Under
hormonalstimulation, males extend their fleshy, colored dewlaps to
courtfemales. This behavior also stimulates hormone release and
egg-laying in the female.
-
Communication inSocial GroupsMany insects, fish, birds, and
mam-mals live in social groups in which in-formation is
communicated betweengroup members. For example, someindividuals in
mammalian societiesserve as guards. When a predatorappears, the
guards give an alarm call,and group members respond by seek-ing
shelter. Social insects, such as antsand honeybees, produce
alarmpheromones that trigger attack be-havior. Ants also deposit
trailpheromones between the nest and afood source to induce
cooperationduring foraging (figure 26.18). Honey-bees have an
extremely complex dancelanguage that directs nestmates torich
nectar sources.
The Dance Language of theHoneybee
The European honeybee, Apis mellifera,lives in hives consisting
of 30,000 to40,000 individuals whose behaviors areintegrated into a
complex colony.Worker bees may forage for miles fromthe hive,
collecting nectar and pollenfrom a variety of plants and
switchingbetween plant species and popula-tions on the basis of how
energeti-cally rewarding their food is. Thefood sources used by
bees tend tooccur in patches, and each patch of-fers much more food
than a singlebee can transport to the hive. Acolony is able to
exploit the resourcesof a patch because of the behavior ofscout
bees, which locate patches andcommunicate their location to
hivemates through a dancelanguage. Over many years, Nobel laureate
Karl vonFrisch was able to unravel the details of this
communica-tion system.
After a successful scout bee returns to the hive, she per-forms
a remarkable behavior pattern called a waggle danceon a vertical
comb (figure 26.19). The path of the bee dur-ing the dance
resembles a figure-eight. On the straight partof the path, the bee
vibrates or waggles her abdomen whileproducing bursts of sound. She
may stop periodically togive her hivemates a sample of the nectar
she has carriedback to the hive in her crop. As she dances, she is
followedclosely by other bees, which soon appear as foragers at
thenew food source.
Von Frisch and his colleagues claimed that the otherbees use
information in the waggle dance to locate the foodsource. According
to their explanation, the scout bee indi-cates the direction of the
food source by representing theangle between the food source and
the hive in reference tothe sun as the angle between the straight
part of the danceand vertical in the hive. The distance to the food
source isindicated by the tempo, or degree of vigor, of the
dance.
Adrian Wenner, a scientist at the University of Califor-nia, did
not believe that the dance language communicatedanything about the
location of food, and he challenged vonFrischs explanation. Wenner
maintained that flower odorwas the most important cue allowing
recruited bees to ar-rive at a new food source. A heated
controversy ensued as
546 Part VII Ecology and Behavior
(a) (b)
FIGURE 26.18The chemical control of fire ant foraging. Trial
pheromones, produced in an accessorygland near the fire ants sting,
organize cooperative foraging. The trails taken by the firstants to
travel to a food source (a) are soon followed by most of the other
ants (b).
(a) (b)
FIGURE 26.19The waggle dance of honeybees. (a) A scout bee
dances on a comb in the hive. (b) Theangle between the food source
and the nest is represented by a dancing bee as the anglebetween
the straight part of the dance and vertical. The food is 20 to the
right of the sun,and the straight part of the bees dance on the
hive is 20 to the right of vertical.
-
the two groups of researchers published articles supportingtheir
positions.
The dance language controversy was resolved (in theminds of most
scientists) in the mid-1970s by the creativeresearch of James L.
Gould. Gould devised an experimentin which hive members were
tricked into misinterpretingthe directions given by the scout bees
dance. As a result,Gould was able to manipulate where the hive
memberswould go if they were using visual signals. If odor were
thecue they were using, hive members would have appeared atthe food
source, but instead they appeared exactly whereGould predicted.
This confirmed von Frischs ideas.
Recently, researchers have extended the study of thehoneybee
dance language by building robot bees whosedances can be completely
controlled. Their dances are pro-grammed by a computer and
perfectly reproduce the nat-ural honeybee dance; the robots even
stop to give foodsamples! The use of robot bees has allowed
scientists to de-termine precisely which cues direct hivemates to
foodsources.
Primate Language
Some primates have a vocabulary that allows individualsto
communicate the identity of specific predators. The vo-calizations
of African vervet monkeys, for example, distin-guish eagles,
leopards, and snakes (figure 26.20). Chim-panzees and gorillas can
learn to recognize a large numberof symbols and use them to
communicate abstract con-cepts. The complexity of human language
would at first ap-pear to defy biological explanation, but closer
examinationsuggests that the differences are in fact superficialall
lan-guages share many basic structural similarities. All of
theroughly 3000 languages draw from the same set of 40 con-
sonant sounds (English uses two dozen of them), and anyhuman can
learn them. Researchers believe these similari-ties reflect the way
our brains handle abstract information,a genetically determined
characteristic of all humans.
Language develops at an early age in humans. Humaninfants are
capable of recognizing the 40 consonant soundscharacteristic of
speech, including those not present in theparticular language they
will learn, while they ignore othersounds. In contrast, individuals
who have not heard certainconsonant sounds as infants can only
rarely distinguish orproduce them as adults. That is why English
speakers havedifficulty mastering the throaty French r, French
speak-ers typically replace the English th with z, and
nativeJapanese often substitute l for the unfamiliar English
r.Children go through a babbling phase, in which theylearn by trial
and error how to make the sounds of lan-guage. Even deaf children
go through a babbling phaseusing sign language. Next, children
quickly and easily learna vocabulary of thousands of words. Like
babbling, thisphase of rapid learning seems to be genetically
pro-grammed. It is followed by a stage in which children formsimple
sentences which, though they may be grammaticallyincorrect, can
convey information. Learning the rules ofgrammar constitutes the
final step in language acquisition.
While language is the primary channel of human com-munication,
odor and other nonverbal signals (such asbody language) may also
convey information. However,it is difficult to determine the
relative importance of theseother communication channels in
humans.
The study of animal communication involves analysis ofthe
specificity of signals, their information content, andthe methods
used to produce and receive them.
Chapter 26 Animal Behavior 547
01
0.5 secondsEagle
2345678
0.5 secondsLeopard
01Fr
eque
ncy
(kiloc
ycles
per s
econ
d)
Freq
uenc
y (ki
locyc
lespe
r sec
ond)
2345678
(a)
(b)
FIGURE 26.20Primate semantics. (a) Predators, like this leopard,
attack and feed on vervetmonkeys. (b) The monkeys give different
alarm calls when eagles, leopards, andsnakes are sighted by troupe
members. Each distinctive call elicits a different andadaptive
escape behavior.
-
Orientation and MigrationAnimals may travel to and from a nest
to feed or move reg-ularly from one place to another. To do so,
they must ori-ent themselves by tracking stimuli in the
environment.
Movement toward or away from some stimulus is calledtaxis. The
attraction of flying insects to outdoor lights is anexample of
positive phototaxis. Insects that avoid light, suchas the common
cockroach, exhibit negative phototaxis. Otherstimuli may be used as
orienting cues. For example, troutorient themselves in a stream so
as to face against the cur-rent. However, not all responses involve
a specific orienta-tion. Some animals just become more active when
stimulusintensity increases, a responses called kineses.
Long-range, two-way movements are known as migra-tions. In many
animals, migrations occur circannually.Ducks and geese migrate
along flyways from Canada acrossthe United States each fall and
return each spring.Monarch butterflies migrate each fall from
central andeastern North America to several small, geographically
iso-lated areas of coniferous forest in the mountains of
centralMexico (figure 26.21). Each August, the butterflies begin
aflight southward to their overwintering sites. At the end
ofwinter, the monarchs begin the return flight to their sum-mer
breeding ranges. What is amazing about the migrationof the monarch,
however, is that two to five generationsmay be produced as the
butterflies fly north. The butter-flies that migrate in the autumn
to the precisely locatedoverwintering grounds in Mexico have never
been therebefore.
When colonies of bobolinks became established in thewestern
United States, far from their normal range in theMidwest and East,
they did not migrate directly to theirwinter range in South
America. Instead, they migrated eastto their ancestral range and
then south along the originalflyway (figure 26.22). Rather than
changing the originalmigration pattern, they simply added a new
pattern.
How Migrating Animals Navigate
Biologists have studied migration with great interest, andwe now
have a good understanding of how these feats ofnavigation are
achieved. It is important to understand thedistinction between
orientation (the ability to follow abearing) and navigation (the
ability to set or adjust a bear-ing, and then follow it). The
former is analogous to using acompass, while the latter is like
using a compass in con-junction with a map. Experiments on
starlings indicate thatinexperienced birds migrate by orientation,
while olderbirds that have migrated previously use true
navigation(figure 26.23).
Birds and other animals navigate by looking at the sunand the
stars. The indigo bunting, which flies during theday and uses the
sun as a guide, compensates for themovement of the sun in the sky
as the day progresses byreference to the north star, which does not
move in thesky. Buntings also use the positions of the
constellationsand the position of the pole star in the night sky,
cuesthey learn as young birds. Starlings and certain otherbirds
compensate for the suns apparent movement in the
548 Part VII Ecology and Behavior
26.4 Migratory behavior presents many puzzles.
SanFrancisco
NewYork
LosAngeles
MexicoCity
SummerbreedingrangesOverwinteringaggregationareas
(a) (b) (c)
FIGURE 26.21Migration of monarch butterflies. (a) Monarchs from
western North America overwinter in areas of mild climate along the
PacificCoast. Those from the eastern United States and southeastern
Canada migrate to Mexico, a journey of over 3000 kilometers that
takesfrom two to five generations to complete. (b) Monarch
butterflies arriving at the remote fir forests of the overwintering
grounds and (c)forming aggregations on the tree trunks.
-
sky by using an internal clock. If such birds are shown
anexperimental sun in a fixed position while in captivity,they will
change their orientation to it at a constant rateof about 15 per
hour.
Many migrating birds also have the ability to detect theearths
magnetic field and to orient themselves with respectto it. In a
closed indoor cage, they will attempt to move inthe correct
geographical direction, even though there areno visible external
cues. However, the placement of a pow-erful magnet near the cage
can alter the direction in whichthe birds attempt to move.
Magnetite, a magnetized ironore, has been found in the heads of
some birds, but the sen-sory receptors birds employ to detect
magnetic fields havenot been identified.
It appears that the first migration of a bird is innatelyguided
by both celestial cues (the birds fly mainly atnight) and the
earths magnetic field. These cues give thesame information about
the general direction of the mi-gration, but the information about
direction provided bythe stars seems to dominate over the magnetic
informa-tion when the two cues are experimentally manipulated
togive conflicting directions. Recent studies, however, indi-cate
that celestial cues tell northern hemisphere birds tomove south
when they begin their migration, while mag-netic cues give them the
direction for the specific migra-tory path (perhaps a southeast
turn the bird must makemidroute). In short, these new data suggest
that celestialand magnetic cues interact during development to
fine-tune the birds navigation.
We know relatively little about how other migratinganimals
navigate. For instance, green sea turtles migratefrom Brazil
halfway across the Atlantic Ocean to Ascen-sion Island, where the
females lay their eggs. How dothey find this tiny island in the
middle of the ocean,which they havent seen for perhaps 30 years?
How dothe young that hatch on the island know how to findtheir way
to Brazil? Recent studies suggest that wave ac-tion is an important
cue.
Many animals migrate in predictable ways, navigatingby looking
at the sun and stars, and in some cases bydetecting magnetic
fields.
Chapter 26 Animal Behavior 549
FIGURE 26.22Birds on the move. (a) Thesummer range of
bobolinksrecently extended to the far Westfrom their more
established rangein the Midwest. When theymigrate to South America
in thewinter, bobolinks that nested inthe West do not fly directly
to thewinter range; instead, they fly tothe Midwest first and then
use theancestral flyway. (b) The goldenplover has an even
longermigration route that is circular.These birds fly from
Arcticbreeding grounds to winteringareas in southeastern
SouthAmerica, a distance of some 13,000kilometers.
Winteringrange
Breedingrange
Holland
Switzerland
Spain
Bobolink Golden plover
Summernestingrange
Winterrange
Summernestingrange
Winterrange
(a) (b)
FIGURE 26.23Migratory behavior of starlings. The navigational
abilities ofinexperienced birds differ from those of adults who
have made themigratory journey before. Starlings were captured in
Holland,halfway along their full migratory route from Baltic
breedinggrounds to wintering grounds in the British Isles; these
birds weretransported to Switzerland and released. Experienced
older birdscompensated for the displacement and flew toward the
normalwintering grounds (blue arrow). Inexperienced young birds
keptflying in the same direction, on a course that took them
towardSpain (red arrow). These observations imply that
inexperiencedbirds fly by orientation, while experienced birds
learn truenavigation.
-
Animal CognitionIt is likely each of us could tell an anecdotal
story about thebehavior of a pet cat or dog that would seem to
suggest thatthe animal had a degree of reasoning ability or was
capableof thinking. For many decades, however, students of
animalbehavior flatly rejected the notion that nonhuman animalscan
think. In fact, behaviorist Lloyd Morgan stated thatone should
never assume a behavior represents consciousthought if there is any
other explanation that precludes theassumption of consciousness.
The prevailing approach wasto treat animals as though they
responded to the environ-ment through reflexlike behaviors.
In recent years, serious attention has been given to thetopic of
animal awareness. The central question iswhether animals show
cognitive behaviorthat is, dothey process information and respond
in a manner thatsuggests thinking (figure 26.24)? What kinds of
behaviorwould demonstrate cognition? Some birds in urban
areasremove the foil caps from nonhomogenized milk bottlesto get at
the cream beneath, and this behavior is known to
have spread within a population to other birds. Japanesemacaques
learned to wash potatoes and float grain to sep-arate it from sand.
A chimpanzee pulls the leaves off of atree branch and uses the
stick to probe the entrance to atermite nest and gather termites.
As we saw earlier, vervetmonkeys have a vocabulary that identifies
specific preda-tors.
Only a few experiments have tested the thinking abilityof
nonhuman animals. Some of these studies suggest thatanimals may
give false information (that is, they lie).Currently, researchers
are trying to determine if some pri-mates deceive others to
manipulate the behavior of theother members of their troop. There
are many anecdotalaccounts that appear to support the idea that
deception oc-curs in some nonhuman primate species such as
baboonsand chimpanzees, but it has been difficult to devise
field-based experiments to test this idea. Much of this type of
re-search on animal cognition is in its infancy, but it is sure
togrow and to raise controversy. In any case, there is nothingto be
gained by a dogmatic denial of the possibility of
animalconsciousness.
550 Part VII Ecology and Behavior
26.5 To what degree animals think is a subject of lively
dispute.
(a) (b)
FIGURE 26.24Animal thinking? (a) This chimpanzee is stripping
the leaves from a twig, which it will then use to probe a termite
nest. This behaviorstrongly suggests that the chimpanzee is
consciously planning ahead, with full knowledge of what it intends
to do. (b) This sea otter isusing a rock as an anvil, against which
it bashes a clam to break it open. A sea otter will often keep a
favorite rock for a long time, asthough it has a clear idea of what
it is going to use the rock for. Behaviors such as these suggest
that animals have cognitive abilities.
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552 Part VII Ecology and Behavior
Chapter 26 Summary Questions Media Resources
26.1 Ethology focuses on the natural history of behavior.
Behavior is an adaptive response to stimuli in theenvironment.
An animals sensory systems detect andprocess information about
these stimuli.
1. How does a hybrid lovebirdsmethod of carrying nestmaterials
compare with that ofits parents? What does thiscomparison suggest
aboutwhether the behavior isinstinctive or learned?
Behavior is both instinctive (influenced by genes) andlearned
through experience. Genes are thought tolimit the extent to which
behavior can be modifiedand the types of associations that can be
made.
The simplest forms of learning involve habituationand
sensitization. More complex associative learning,such as classical
and operant conditioning, may bedue to the strengthening or
weakening of existingsynapses as well as the formation of entirely
newsynapses.
An animals internal state influences when and how abehavior will
occur. Hormones can change an ani-mals behavior and perception of
stimuli in a way thatfacilitates reproduction.
2. How does associative learningdiffer from
nonassociativelearning? How does classicalconditioning differ from
operantconditioning?3. What is filial imprinting?What is sexual
imprinting? Whydo some young animals imprinton objects like a
moving box?4. How does Marlers work onsong development in
white-crowned sparrows indicate thatbehavior is shaped by
learning?How does it indicate thatbehavior is shaped by
instinct?
26.2 Comparative psychology focuses on how learning influences
behavior.
Animals communicate by producing visual, acoustic,and chemical
signals. These signals are involved inmating, finding food, defense
against predators, andother social situations.
5. How do communicationsignals participate inreproductive
isolation? Give oneexample of a signal that isspecies-specific. Why
are somesignals individually specific?
26.3 Communication is a key element of many animal
behaviors.
Animals use cues such as the position of the sun andstars to
orient during daily activities and to navigateduring long-range
migrations.
6. What is the definition oftaxis? What are kineses? Whatcues do
migrating birds use toorient and navigate during
theirmigrations?
26.4 Migratory behavior presents many puzzles.
Many anecdotal accounts point to animal cognition,but research
is in its infancy.
7. What evidence would youaccept that an animal isthinking?
26.5 To what degree animals think is a subject of lively
dispute.
www.mhhe.comraven6e www.biocourse.com
On Science Article:Polyandry in Hawks