Animal Communication Flashcards
Introduction to animal communication
Communication is at the heart of much of social behavior.
- Signal –a feature or behaviour of one individual (producer) that influences the behaviour, or future behaviour, of another individual (receiver), and that evolved specifically for that purpose.
- Cue – any feature or behaviour that can be used to guide future action
Signals evolved specifically to communicate. Cues did not.
Sensory modalities (ways of communicating) - visual, vocal, olfactory (smell), tactile (smell), electric
Signalling involves signallers and receivers:
Group members(e.g. alarm calls)
Mates(e.g. courtship signals)
Rivals(e.g. aggressive signals)
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Signal evolution:
•Two crucial conditions for a signal to evolve
1) From the production side
Signal needs to be informative
•That is, a signal (e.g. alarm call) predictably indicates (correlates with) a specific feature (e.g. predator)
•Only then it is useful for the receiver
2) From the receiver’s side: The receiver is able to perceive, and can adjust its behaviour (e.g. hiding from a predator) in accordance with, the signal. Receivers evolved specific perceptual means to receive the signal and to adjust their behaviour accordingly.
Ritualization - the making of a signal:
Cue is gradually converted into a signal (during evolution)
1) A cue (that is useful for the receiver) is ‘picked up’ or paid attention by the receiver
2) Gradually, the receiver attends to more and more elaborated (less ambivalent) ‘cues’
3) Therefore, the signaller is ‘forced’ to elaborate the ‘cue’ more and more
Outcome: conspicuous, stereotyped and repetitive signalling behaviours (to ensure receiver’s response), e.g. courtship dance in some birds
Signals and future behaviour:
Signals are often about subsequent behaviour of the signaller that, e.g.:
-signal aggressive intentions (e.g. growling)
-signal affiliative intentions
-coordinate behaviour with partner/group members
Signals allow the receiver to predict the behaviour of the producer, and to adjust its behaviour accordingly (benefits both parties)
Predicting others’ behaviour - an example:
•Taking off ‘without warning’ causes the whole flock to take off too
•This is an antipredator strategy (startled birds take off just in case)
•Hence, many birds evolved “take-off signals” to signify an intention to fly
•Taking off after performing the ritual does not startle the flock
For example, sky-pointing behaviour in blue-footed booby. the wings are wide open and rotated at the shoulder with the beak and the neck facing the sky. this is a very sophisticated, conspicuous signal because signalling taking off in this species is especially important.
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Signals are sent and received by individuals, both within and between populations, and even between species. There are many different senses that are employed during bouts of communication.
Some environments are extremely “noisy,” making it difficult to send and receive signals.
For example, the “soundscape” of an environment like the tropics is noisy and complex, making communication especially difficult (Planque and Slabbekoorn, 2008). In such auditory soundscapes, natural selection should favor communicating in ways that maximize the chances that auditory signals are not masked.
Evidence suggests that in neotropical rainforests, birds in one species monitor the auditory communication of birds in other species and adjust their own communication to minimize the chances that their
own signals are masked (Luther, 2009). But the soundscape in neotropical rainforests also includes signals from insects, mammals, and even amphibians. Cicada species, for example, can be very noisy.
Patrick Hart and colleagues hypothesized that neotropical birds might try to partition the soundscape with cicadas to increase the chances that their signals are not masked (Hart et al., 2015). In particular, they tested the prediction that birds in the Costa Rican
rainforest would partition the soundscape with Zammara smaragdina, a species of cicada that sings often and loudly in this environment, using a very broad band spectrum that could mask many bird songs.
The mean number of bird species singing, and the mean number of bird vocalizations, were both significantly lower in the 15 minute period after the cicadas started singing compared to the fifteen minutes before.
In the cases when birds did sing concurrently with the cicadas, they used sounds that did not overlap with the frequencies of the sounds used by the cicadas. What’s more, on the few days when cicadas did not sing at all, the birds changed their singing patterns during the time period cicadas normally sing, suggesting that it was the cicada song per se that birds were responding to.
Ethologists typically define communication as the transfer of information from a signaler to a receiver. Communication is inherently social—it involves
more than a single individual—and communication conveys information that is necessary to solve some problem or another.
Communication and Honesty
Signal evolution - ensuring reliability
Condition: signalling can evolve only when it benefits both the signaller and the receiver
Problem: Signallers can manipulate the behaviour of the receivers to their own advantage by emitting false information
How to ensure signal reliability?
this is important, otherwise signals would not evolve. if signals were not useful for the producers to, they would simply stop producing the signal or the receivers would ignore the signal.
Ensuring signal reliability –three ways
•When interests of signallers and receivers converge (faking a signal is not beneficial for both parties)
•Indexes of quality (impossible to fake –e.g. imposed by anatomical constraints of the signaller)
•Costly signalling (very difficult to fake –imposed by costs of signalling, requires energy to produce it)
Signalling when interests converge - social insects:
we are likely to have honest signalling when interest of signallers and receivers converge. however, totally convergent interests are surprisingly rare in nature. usually relationships are based on conflict. However interests do converge in some animal species, including bees, individuals such as workers are genetically highly related to each other and to their mother.
in such situations due to high relatedness between individuals, it is beneficial to behave altruistically towards other workers and to the mother to produce more highly related systems. this includes sharing information about food and peace by communicating. what is especially interesting about bee communication is that its level of complexity according to some scientists, almost approaches the level of complexity of human communication. for example, after harvesting polin inside the hive, bees can communicate to other bees several pieces of quite sophisticated information about the source of food (distance and direction).
such altruistic behaviour have also been recorded in other social insects characterised by such animals as ants who mark a trail on return from a food source to make it easier for others to locate the food.
Signalling when interests converge - alarm calls:
Three types of alarm calls -
Raptor - cough call
Leopard - barks
Snake - chuttercall
Seyfarth & Cheney 1980
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Regardless of the problem a communication network is in place to solve, we can ask whether natural selection should favor honest signals or deception.
Dawkins and Krebs argue that communication is not so much the exchange of information between a signaler and a receiver but rather an attempt by the signaler to manipulate the recipient. They recognize that sometimes what is in the best interest of the signaler is also in the best interest of the recipient. But when what is good for the signaler is not good for the recipient, natural selection will favor signalers that send signals in whatever way best increases the fitness of the signaler, even if that means manipulating recipients. Natural selection will also favor recipients with the ability to unscramble what is honest and what isn’t, so it can act in ways that maximize its own fitness.
This is a different view from what Dawkins and Krebs refer to as the classic ethological approach of communication (Marler, 1968; W. J. Smith, 1968, 1977; N. Tinbergen, 1964). Implicit in the classic approach is that both parties usually benefit from the information
exchange, and there is little selection pressure for either to be deceitful: the signaler and receiver have common interests, and selection favors the most economical way to share information.
Krebs and Dawkins offer a way to distinguish between cases in which there is an arms race between manipulators and mind readers, and those in which cooperative signaling dominates. Krebs and Dawkins propose that when communication is of the manipulator/mind-reader type, signals employed should be exaggerated, as one might expect from a salesman attempting to convince a prospective buyer that his product is the top of the line.
When cooperative signaling is in play, natural selection should favor less exaggerated signals—what Krebs and Dawkins refer to as conspiratorial whispers. Because signaling often involves some costs —for example, energy costs or drawing attention from predators—
natural selection should favor minimizing these costs through conspiratorial whispers, which reduce the conspicuousness of the communication itself (De Backer and Gurven, 2006; R. A. Johnstone, 1998; Noble, 1999).
The formal mathematical models of the conspiratorial whispers versus conspicuous display hypotheses is a useful heuristic tool. There is, however, another means besides cooperative signaling by which we might expect communication to be honest. Honesty might evolve if the signals being sent are either impossible or, at the very least, difficult to fake.
As an example, imagine that females produce more offspring when they mate with larger males. All males, even small ones, would be favored when they produced signals that make it appear to a female that they were large. But selection should favor females paying attention only to those cues that are honest indicators of large size. Females should cue in on honest signals.
This appears to be the case in toads: Deep croaks can
be produced only by large males because of the physiology of their vocal system. Because male toads can’t fake deep croaks and females prefer larger males as mates, female toads can use croaks as an honest signal when choosing among males (Davies and Halliday, 1978).
Amotz Zahavi has suggested that honesty is also possible when traits are not impossible but just very costly to fake (Grafen, 1990a,b; Zahavi, 1975, 1977, 2003; Zahavi and Zahavi, 1997). Under Zahavi’s
handicap principle, if a trait is costly to produce, it may be used as an honest signal, because only those individuals that can pay the cost will typically adopt the signal in question. For example, imagine that females are using the length of a male’s energy-costly song as a cue for the amount of resources he is able to garner.
While a male that is not good at garnering resources could potentially use virtually all of his resources to sing, and thus could give the female a false impression of his resource-garnering skills, most often only the males that are genuinely good at gathering resources would be able to afford to sing, as singing is an energy-costly activity. Honest communication may be an outcome even when deception is possible in principle, as long as deception is costly (E. Adams and Mesterton-Gibbons, 1995; R. A. Johnstone, 1995, 1998; Mesterton-Gibbons and Adams, 1998; Zahavi and Zahavi, 1997).
Communication Solves Problems
ethologists have also examined communication at a broader level, not confined to a single behavioral context. For example, Karen McComb and Stuart Semple studied the relationship between vocalization and group size in primates (McComb and Semple, 2005). When these researchers examined the published literature and compared vocalization
repertoire—the number of different vocalizations used—and group size, they found a significant positive correlation.
One possible explanation for this finding is that as group size increases, the benefits of a broad repertoire of sounds to communicate with other group members increases (Snowdon, 2009). However, because
McComb and Semple’s study was correlational, it is not clear yet whether increased group size favored increased vocalization repertoires or whether increased vocalization repertoire favored the evolution of increased group size (Freeberg et al., 2012) or both.
• Problem: How to Coordinate Group Foraging
When animals forage in groups, they face coordination problems. When new food sources are found, how can that information be transferred to other group members if such a transfer is beneficial to the signaler (Dornhaus et al., 2006; Fernandez-Juricic and Kowalski, 2011; Fernandez-Juricic et al., 2006; Galef and Giraldeau, 2001; J. R. Stevens and Gilby, 2004; Thierry et al., 1995; Torney et al., 2011)?
Food Calls in Birds:
Colonial breeding cliff swallows (Petrochelidon pyrrhonota) live in nests that act as information centers (C. R. Brown, 1986; Ward and Zahavi, 1973). For some time, researchers thought that individuals living in nests passively received information—they simply observed
their nestmates and followed them to potential resources. While this sort of system does allow for group foraging, it is not as efficient a solution to coordinating group behavior as recruiting foragers.
Charles Brown and his colleagues studied whether individuals are recruited to food sites (C. Brown et al., 1991). Brown and his team found that cliff swallows gave off “squeak” calls, which alerted conspecifics that a new food patch—often a swarm of insects—had been found. Squeak calls were emitted only in the context of recruiting others to a food site, suggesting that they served the specific function of facilitating group foraging, per see.
Recruiters also obtain benefits from calling because the increased group size that results from recruiting makes it more likely that some group members will find and track the insect swarm and thus provide further foraging opportunities (C. Brown, 1988; C. Brown et al., 1991). This tracking behavior may be important, as swallows must often return to the colony to provision young, and might have difficulty relocating an insect swarm without the help of others. As well as Swallows, ravens who are scavengers can often survive for days if they uncover a large food patch. they often emit a loud yell attracting other ravens to the caller’s newly discovered bounty (Boeckle et al., 2012).
Bernd Heinrich and John Marzluff (Corvus corax; Heinrich, 1988a,b; Heinrich and Marzluff, 1991).
On the proximate end, it appears that yelling is a response to hunger level. In terms of the costs and benefits of calling, it appears that yelling by juvenile ravens attracts other juvenile ravens to a food resource, allowing them to overpower resident adult ravens.
Marzluff and his team studied juvenile ravens in Maine, where individuals form roosts near a newly discovered food source—for example, a large animal carcass. They found that such roosts are very mobile and ravens move to where new prey has been discovered. Marzluff’s team hypothesized that these mobile roosts served as information centers that provided roost mates to share information about prey discovered away from the roost. evening roosts contain knowledgeable individuals that know about nearby prey, and naive individuals that do not. they communicate with one another, and that one or a few knowledgeable individuals lead the way.
In one experiment, Marzluff found that the same individual would act as a leader when it learned the location of new prey, and as a follower when it was denied information that others in the nest knew. While it is not clear exactly how information about who is a knowledgeable forager and who is not is spread at the roost, researchers noted that before the ravens departed from the roost in the morning, they emitted “honking” sounds. Whether knowledgeable birds were more likely to emit such sounds remains to be tested.
Reciprocal signaling in honeyguide-human: interspecies signalling (signalling between two different species). a honey-guide bird leads people to beehives, people then harvest the honey and then reward the bird with a piece of honeycomb. this interaction benefits both parties, the bird would not be able to get to honey on its own and people would not be able to locate the honey. this is why this communicative system evolved, because it benefits both parties. However, this system to evolve after harvesting the honey, people must reward the bird otherwise the signal would not evolve or the bird would simply stop behaving this way.
Honeybees and the Waggle Dance:
In honeybees, collecting food for the hive often involves thousands of workers covering large areas (Visscher and Seeley, 1982). The waggle dance of the honeybee was first studied experimentally by Karl von Frisch (von Frisch, 1967). Upon returning to the nest, the worker bee quickly starts “dancing” up and down a vertical honeycomb within the hive; her sisters and half-sisters stay near her, making as much physical contact as possible with both her and each other in the process. While dancing vigorously by waggling her abdomen, the worker conveys crucial information to her relatives in the hive.
The dance provides topographical information (north, east, south, west, northwest, and so on) for finding the food source from which she has just returned. The angle at which the forager dances provides information about the position of the food source of interest in relation to the hive and to the sun. Furthermore, the longer the bee dances— the waggle dance known as the “straight line”—the farther away the bounty. The more precise the information conveyed in the waggle dance, the greater the ability of other bees to find the food source, the more food brought back to the hive, and consequently the greater the inclusive fitness of the forager, because a hive is largely composed of individuals that are closely related to one another.
Ross Crozier and his colleagues studied the genetics of the honeybee dances by examining the point at which bees shift from other types of dances to the waggle dance (Johnson et al., 2002; Oldroyd and Thompson, 2007; Oxley and Oldroyd, 2010). When resources are close to the hive, honeybee foragers tend to use what is called a round dance. When the resources are at greater distances, bees switch to a sickle dance, and when food is very far from a hive, foragers use the waggle dance.
Crozier and his team ran many experiments in which they mated individuals from populations of bees that differed in terms of when they shifted from using the round to the sickle dance, and when they shifted from the sickle to the waggle dance. For example, the researchers studied bees transitioning from the round to the sickle dance when food was more than 20 meters from the hive, and they shifted from the sickle dance to the waggle dance when food was 60 meters or more from the hive. The results of the genetic crosses undertaken by Crozier and his colleagues suggest that the transition across dance types is controlled at a single locus (Johnson et al., 2002).
Ethologists also studied developmental changes with the honeybee waggle dance. Jurgen Tautz and his colleagues examined how hive temperature during development affected the waggle dance behavior of bees (Tautz et al., 2003). The researchers observed differences in the waggle dance behavior in bees raised at different temperatures. The results suggest that differences in temperature during early development can have important effects on the bees and the hive. When bees were raised in colder temperatures, they were both poor learners and less efficient at communicating important foraging-related information to other members of their hive. Lower temperatures lead to bees that are both poor foragers and poor communicators, which in turn leads to less energy for the hive and hence to lower hive temperatures, which then leads to even worse foragers, and so on.
SUMMARY
research question - How does the honeybee waggle dance communicate information to would-be foragers?
The honeybee waggle dance is one of the few instances of nonhuman communication where place and time are communicated symbolically.
Many different approaches have been taken to address the research question, including recording behavior within hives, experimental manipulation of foraging sites, manipulation of the hive environments, genetic breeding studies, and molecular genetic analyses
have been employed to study this question.
The discovery was that two of the key components of the waggle dance convey the location of food sources to naive foragers are the angle that a returning forager uses during the straight run part of the waggle dance (an indication of compass direction) and the duration of the straight run (indicating distance from the hive). Both convey information about the location of food sources to naive foragers.
The results mean that animals are capable of complex,
sophisticated forms of communication, some of which use symbolic representation.
• Problem: How to Find and Secure a Mate
Animals use many different types of communication when assessing potential mates. In this section, we will examine the role of (1) vocal communication (birdsong) and (2) tactile communication (ripples by insects that live in water), as they relate to intrasexual and intersexual selection.
Birdsong:
Birdsong has many functions associated with colony formation, flocking, foraging, and other behaviors (Kroodsma and Byers, 1991), but here there is a focus on its role in sexual selection. In most species of songbirds, males don’t just learn a song; they learn many different songs. Because repertoire size may be a proxy cue for a male’s age and/or genetic quality, ethologists have hypothesized that females may use the size of a male’s song repertoire when choosing between mates (Hosoi et al., 2005; MacDougal-Shackleton, 1997).
Aki Hosoi examined, does the number of different songs a male sings affect his mating success?
This an important question because some work suggests that the size of a male’s song repertoire affects his mating success, but whether females
prefer large song repertoires in males was not known.
The approach taken to address the research question - Female brown-headed cowbirds (Molothrus ater) were exposed to males that sang different numbers of songs. Males were from either the same population as the female, a different cowbird population, or a different species.
The discovery was Females engaged in more copulation-solicitation displays when exposed to cowbird males with larger song repertoires.
Ripple Communication and Mate Choice in Aquatic Insects
In 1972, Stim Wilcox discovered a new form of communication called ripple communication in water striders, insects that live in freshwater lakes, ponds, streams, and small rivers. In water striders, ripples are
typically produced by an up-and-down movement of the legs, with both right and left legs in synchrony and in contact with the water surface (Wilcox, 1995). The water striders produce ripples: waves with different amplitudes and frequencies for different kinds of behaviors, including signals for calling mates, courtship, copulation, postcopulation, mate guarding, spacing, territoriality, and food defense.
Wilcox ran playback experiments that demonstrated that females from as far away as 60 cm were attracted to mating ripple signals—ripples that are different from those produced by aggressive males (Wilcox, 1972). Females would often grasp males and even begin to
oviposit (lay eggs) in response to playbacks of calling signals. In addition, Wilcox hypothesized that ripple calls designed to attract mates also serve as a means for species identification, as R. anomalus are often found in the same streams and ponds as other water striders (Polhemus and Karunaratne, 1993).
• CONSERVATION CONNECTION: Anthropogenic Change and Animal Communication
The type of communication system that natural selection favors in a population depends, in part, on the ecology and environment in which that species lives. For example, many forest-dwelling birds that breed in leks will display courtship behavior only when the light breaks through the forest canopy through small gaps at certain times of the day.
Altering that environment can disrupt courtship activity.
In the Guianian cock-of-the-rock (Rupicola rupicola), orange-colored males will often display to females when yellow-orange wavelength light from small gaps in the canopy reaches the ground (Endler, 1997; Endler
and Thery, 1996). The courtship dance and song that then takes place is dramatic, as described by Pepper Trail, who studied these birds in Suriname: “The normally silent males burst into ringing choruses of
raucous, crowing calls and drop from their resting perches. . . . Each male stands erect and violently beats his wings, flashing the dramatic, usually concealed, black and white primary feathers” (Trail, 1995). Males may then repeat this greeting display (Figure 13.16), and females choose from among the displaying males.
Humans clear-cutting the area of the lekking arena, or even areas in its vicinity, will change the way light enters the lekking arena and might radically disrupt the courtship communication between male and female
cock-of-the-rocks (Endler, 1997). Of course, it is difficult to predict exactly how, but such clear-cutting might produce constant light during daytime hours, which could (1) stop males from displaying at all because of
increased exposure to predators, (2) induce males to display so often that they become energetically drained, or (3) lead to females no longer being able to assess male quality accurately. Any or all of these effects could affect population size.
• Problem: Predators
Vervet monkeys living in the Amboseli National Park in southern Kenya face danger from many predators. When encountering these predators, vervets communicate information in a remarkable fashion. Vervets emit specific alarm calls for specific types of danger and different calls elicit different responses by groupmates (Cheney and Seyfarth, 1990; Manser, 2013).
When an eagle is spotted, vervets emit a “cough” call. When other vervets hear the cough call, they look into the air or hide in the bushes, where they tend to be safe from avian threat. If a leopard is spotted, a “barking” alarm call is given, and vervets respond by heading up trees, where their agility makes them relatively safe from leopard attacks. When a python or cobra is sighted, vervets emit a “chutter” call. Since snakes often hunt vervets by hiding in the tall grass, a chutter call gets other vervets to stand and scan the grass around them for snakes.
the receivers respond differently depending on the type of call. if they hear an eagle call they run to the bushes for safety (safest option for kind of predator), hearing a leopard alarm call is when they run up the tree (safest option), and for the snake alarm they scan the ground and approach the snake to morbid. this is semantic communication; different sounds signalling different features in the environment. this is why the signals are called functional referentiality signals.
This sort of complex alarm calling has also been found in other primates such as chimpanzees and tamarins, as well as in birds (Crockford and Boesch, 2003; Crockford et al., 2012; Kirchhof and Hammerschmidt, 2006; Suzuki, 2016). In blue monkeys (Cercopithecus mitis), males not only give specific alarm calls for specific predators but they can gauge the distance of predators from the alarm calls given by others in their group (Papworth et al., 2008; Zuberbuhler, 2009). For more about the complex, often cognitively challenging aspects to communication and signals in the context of
predation.
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Development, Learning, and Alarm Call Communication in Meerkats
When parental care is present and lengthy, natural selection will often favor developmental pathways in which young individuals learn about communicative signals from adults (Platzen and Magrath, 2005). This
should be especially true when signals are complex, as in the alarm calls of vervets. Indeed, the evidence suggests that young vervets do learn about alarm calls from older individuals (Seyfarth and Cheney, 1986).
Meerkats also have prolonged parental care and learn complex alarms calls for terrestrial and avian predators.
Meerkat pups spend the first three weeks of their lives underground, and then they emerge and join groups of juveniles (six to twelve months old) and adults. Once above ground, pups are subject to predation pressure from avian and terrestrial predators.
Linda Hollen and Marta Manser examined the development of the response to alarm calls in maturing meerkat pups (Hollen and Manser, 2006). They studied eleven groups of free-ranging meerkats in the Kalahari Desert, using both data from the field and experimental manipulation through playback experiments in which meerkats were exposed to recorded alarm calls.
Behavior observations indicate that, compared with adults, pups initially were more likely than adults to ignore alarm calls emitted in the presence of dangerous predators and don’t react appropriately to alarm calls as adults do. After hearing an alarm call, pups often moved to shelter when they observed adults only briefly looking up and scanning for aerial predators.
And even when pups displayed antipredator behaviors
similar to those of adults, they reacted more slowly than did adults. As time passed, however, pups began to display more adultlike, adaptive, responses to alarm calls, and evidence strongly suggests that these changes are in part due to pups learning about alarm calls and predators from adults (Hollen et al., 2008).
——————————————————————————–When Not to Pay Attention to Signals
When signals such as alarm calls become less reliable, natural selection should favor paying less and less attention to them. This raises the question of whether animals that receive inaccurate information from a signaler respond by eventually ignoring the signaler
(Beauchamp and Ruxton, 2007; Blumstein et al., 2004; Hollen and Radford, 2009).
James Hare and Brent Atkins examined this in Richardson’s ground squirrels (Spermophilus richardsonii). Hare and Atkins designed an experiment with juvenile ground squirrels in one of two treatments. In one treatment, juveniles heard a recorded alarm call and then saw a predator repeated ten times (a stuffed badger). In a second treatment, ground squirrels heard an alarm call repeated ten times, but now they did not see a predator (Hare and Atkins, 2001).
Hare and Atkins examined how long the squirrels remained vigilant and the extent to which juvenile squirrels in the two treatment conditions turned in the direction from which an alarm call emanated
(postural change). No differences across the two groups were found in their response to the first alarm call, which was expected, as the squirrels had no knowledge beforehand as to which alarm calls would
be reliable and which would not. Even after hearing five alarm calls, there was a difference in postural change: Squirrels that had heard unreliable calls were less likely to look in the direction of the call than were squirrels that had heard reliable calls. After hearing the alarm call ten times, differences in vigilance duration between the two groups of squirrels emerged.
Squirrels in the group in which the alarm was paired with a reliable caller responded to alarm calls
by remaining vigilant and looking in the direction of the call. Squirrels in the other treatment ignored the alarm calls, and they were unlikely to look in the direction from which the calls emanated. Given enough information, Richardson’s ground squirrels can distinguish between reliable and unreliable calls (Pollard and Blumstein, 2012).
Can Elephants Distinguish Between Humans Based On Voice?
Elephants in the Ambosseli National Park face many dangers, including threats from humans. But, the threat that humans present to elephants differs across the ethnic group, sex, and age of the humans involved.
Maasai pastoralists, who spend much time grazing their cattle, are more dangerous to elephants than are individuals from the Kamba, because the former sometimes come into conflict with elephants over access to watering holes and grazing patches, while the latter do not (Moss et al., 2011).
On occasions when Maasai pastoralists spear elephants over conflicts associated with grazing sites, it is Maasai adult males, not adult females or children, that attack the elephants. Prior work had demonstrated that elephants could distinguish between Maasai and Kamba people based on olfactory cues (Bates et al., 2007). Karen McComb and her team wanted to know whether elephants could use human voice to discern the level of threat posed by a human (McComb
et al., 2014; Plotnik and de Waal, 2014).
They presented playbacks of human voices to forty-eight elephant family groups and noted the response
of the elephants. Depending on which type of human voice they heard, the elephants displayed differences in defensive behaviors, including bunching together, listening, smelling, and retreat behavior. The elephants’ defensive behaviors were stronger in response to voices that were associated with human groups that were more dangerous: defensive behaviors were
stronger in response to Maasai adult males vs. Kamba adult males, Maasai males vs. Maasai females, and Maasai adult males vs. Maasai boys
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SUMMARY
What is the research question?
Can elephants gauge how dangerous humans are using vocal cues?
Why is this an important question?
If animals can use signal characteristics to gauge how likely a signaler was to be dangerous, such a trait would be favored by natural selection.
What approach was taken to address the research question?
The behavior of elephants was noted in response to playbacks of human voices that were associated with different levels of threat to the animals.
What was discovered?
Elephants displayed more defensive behaviors
when exposed to human voices that were associated with greater risks.
What do the results mean?
Elephants use human vocal cues to detect differences associated with risk between humans from different populations (the Maasai, who sometimes kill elephants, and the Kamba, the who rarely do), different sexes (human males are more dangerous than females), and
age (older humans are more dangerous than children).
Signalling when interests DO NOT converge
- Indexes of quality (impossible to fake –e.g. imposed by anatomical constraints)
- Costly signalling (very difficult to fake –imposed by costs of signalling)
Indexes - body size:
indexes simply cannot be fake because of anatomical constraints such as body size. tree marking is seen in some territorial mammals; tigers stand on their hinde legs and scratch the bark of the tree, bears rub their back against a tree. both outcomes are the same; a genuine proof of body size and directed at rival males.
this signal is genuine as the height at which the mark is left can not be faked, it is constrained or limited by body size by the signaller. If tigers or bears could learn how to stand on a box, the signal would no longer be reliable.
animals can also signal their body size by vocalising; low-frequency calls from larger toads deter smaller toads male challengers when guarding females.
Indexes - physical condition:
Stotting in gazelles
two meanings - has discovered the predator and they are in very good physical condition.
Discourages predators from pursuit.
Beneficial for both parties.
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Another way of ensuring signal reliability is;
The handicap principle: receiver-driven mechanism for signal reliability (by Amotz Zahavi)
STEP BY STEP;
•Receivers attend to reliable (honest) signals
•Honesty is ensured by costs of signalling
•Due to these costs, signals are more likely displayed by high-quality (or highly motivated) individuals
•Cheating is unlikely (due to costs associated with signalling)
•Hence, the more costly (and hence reliable) the signal is, the more likely the receiver is to attend to it •Outcome –elaborated, conspicuous, costly signals
Signals are reliable because of, not in spite of, costs
Costly signalling - courtship signals
Knapp & Kovach 1991 (costly signalling in damselfish)
- Exclusive paternal (male) care
- Females choose males based on energetic displays
- Display honest signal of male condition
this study showed that these displays correlate with male physical condition, this is probably why there is a positive relationship between may displace and egg survival.
another example in house finches plumage brightness correlates with fitting the visits to nests and therefore with food provision potential. this is why they prefer brightly coloured males, importantly, Carotenoids cannot be synthesized, so they provide an honest measure of a male’s foraging ability.
honesty of begging:
in some bird species there’s a positive relationship between begging and need, therefore begging is an honest signal of need or hunger.
how is this honesty maintained? what is the mechanism behind it?
1)Begging is costly – it attracts predators. Artificial nests (on the ground) were more likely to be predated if begging calls were played.
•Ground-nesters more prone to predation
•Produce higher-pitched begging calls
•High-frequency sounds do not travel as far
These high-pitched begging calls are used to confuse the predator, not attract help.
2) Begging is energetically costly: only pays off when really in need. parental investment is beneficial for offspring to demand more food than the parent is prepared to give. however, the genetic cost associated with begging makes it difficult for chicks to exploit a parent. so begging only pays off when really needed otherwise, the costs of begging outweigh the gains. (Kilner, 2001) study shows that showed that chicks that call for longer have lower body mass, so begging does incur costs.
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Costly signalling: human equivalents
Conspicuous consumption
Display of wealth
these signals are honest because poor individuals do not have enough resources to produce these kinds of displays/signals.
Excess of resources - an honest display of wealth
evolutionary mechanisms behind cost:
(two possibilities)
- sexual selection
- social selection; such signals are associated with prestige in the society and associated political benefits.
communication: four levels of explanation
why do barn swallow males sing?
1) Because of high levels of testosterone
2) Because they learn singing from neighbour males
3) Because they inherited that behaviour from ancestors
4) To attract females / repel rival males
all of the answers are correct but they explain vocal signalling on several different levels (they are not mutually exclusive). they are still kind of independent because to understand ultimate level explanations, we don’t necessarily need to understand proximate level explanations. but to have a proper picture of a given behaviour we need to have both ultimate level and proximate level explanations.
explanations one and two are so called proximate levels of explanations. they refer to the mechanism of vocal production and to the ontogenetic development of calling (so how calls are generated on the anatomical or physiological level, what are the mechanism involved in signalling and how signalling changes during optogenetic development).
for example, it could be socially learned from other individuals.
explanations three and four are so called ultimate-level explanations. they refer to function and evolution. what is the ultimate function? what is the purpose? why is singing adaptive? and how it does it evolve?
how similar or how different animal communication is from human communication
Language is functionally complex
-Multiple information transfer
Language is structurally complex
- Semantics
- Syntax
Are animal calls functionally and structurally complex?
non-human primates such as apes can be especially informative because they are evolutionary closely related to humans.
Are chimpanzee calls functionally and structurally complex?
Agonistic (aggression) calls - screams and ‘waa’ barks
more than just screams, victims of aggression produce sometimes so-called ‘waa’ barks which are produced during the same vocal sequence of screams. the questions was whether and how these barks are different from screams especially in terms of function.
they appear to be different on the spectrum with screams being more tonal and high pitched than the more noisy and lower pitched ‘waa’ barks. but you may admit that it’s not easy for us to distinguish between these two. this is because by only listening to them, to us the sounds are so similar to each other.
A chimpanzee however would not make any mistake here. these two types of called are directed at different audiences and have different functions. for example, victims of aggression were more likely to scream, but not ‘waa’ bark when potential helpers such as adult males were nearby suggesting that these calls function to recruit help.
furthermore, after ‘waa’ barking but not screaming, victims were more likely to retaliate against the aggressor, suggesting that the function of the ‘waa’ bark is to repel the opponent. so screams and barks produce a part of the same vocal sequence, but directed at different audiences and play different functions.
a similar principle applies to another chimpanzee called the Pant Hoot, a Pant Hoot is acoustically complex, because it compromises 4 distinct phases; the introduction, build-up, climax and let down. these 4 phases are associated differently with 4 different kinds of information.
introduction - identity, age
build-up - age
climax - dominance, identity
let down - activity (what they do)
chimpanzees can probably recognise each other through the introduction or climax part of the call.
Victims were more likely to scream (but NOT ‘waa’ bark) when potential helpers were nearby (Fedurek et al, 2015)
