Animal Behavior: Chapter 51
Animals can behave socially or on their own, in fixed or variable ways, based on their physiological systems. Animal behavior is is an action carried out by the muscles of the animal in response to a certain stimulus. This chapter explains how animal behavior is developed, controlled, and how it is influenced by genes and the environment.

How do animals behaviors develop?
Scientists ask this question to try and determine what functions certain animal behaviors accomplish and how they arose in the first place. Niko Tinbergen was a pioneer in the field animal behavior and developed the following questions to try and understand any animal's behavior:
  • What stimulus elicits the behavior, and what physiological mechanisms mediate the response?
  • How does the animal's experience during growth and development influence the response?
  • How does the behavior aid survival and reproduction?
  • What is the behavior's evolutionary history?

These questions fall under two categories of animal behavior inquiry. The first two ask about proximate causation: the how a behavior is modified or occurs. The last two ask about ultimate causation: the why a behavior arises in terms of natural selection and evolutionary history. These questions define behavioral ecology: the study of ecological and evolutionary basis for animal behavior.
51_02SticklebackSignStim-U.jpg
The different sticklebacks and decoys


Basic Animal Behaviors:
There are many types of animal behavior. A fixed action pattern is when an animal responds to a stimuli without having to learn the behavior; it happens naturally. An example is with some fish that Tinbergen experimented with. He used fish called sticklebacks and moved different colors and shapes of fake fish in front of the male sticklebacks' tank. Male sticklebacks behave aggressively when another male enters their territory, and males have distinctive red markings on their bellies, whilst females are solid colored. Decoy fish of any shape, even unrealistic ones, with red bellies would cause the stickleback to try to attack. This is an example of sign stimulus, as the sign of the red belly stimulates the male stickleback to behave aggressively. Since the fish does this without ever having to learn this behavior, it is also an example of the aforementioned fixed action pattern.

Animal behavior is also influenced by the environment. For example, animals use environmental cues to know when to undergo migration, which is a regular, usually annual, long-distance change in location. In order to find their way through unknown territory, animals use several different techniques. They can use the sun and stars for navigating, and some animals can even sense their position relative to the earth's magnetic field and will navigate using that information.

Animals also behave in rhythms. The most common is the circadian clock, an intangible time-keeping mechanism that animals use to determine night from day and thus establish certain patterns in their behavior. The circadian clock doesn't only help keep track of day and night, it also tell certain animals when to hibernate and when to wake up. Migration and reproduction are also rhythmic behaviors, as they happen annually (called circannual rhythms) or monthly or something along those lines. Daylight and nighttime also play roles for these longer rhythms: if an animal is constantly exposed to unnaturally extended daylight then it will induce out-of-season migration. Some animals also use the moon to determine rhythms. For example, fiddler crabs will determine mating season after a certain amount of tidal stages, which also correlates with the phases of the moon.

Animal Communication:
A stimulus transmitted from one animal to another is called a signal, i.e., a bird's call. This transmission and reception of signals is called communication. There are enormous amounts of forms of animal communication, including for courtship, pack behavior, warnings, and many others. The most common modes of animal communication are visual, chemical,
51_06MinnowResponse-U.jpg
Example of pheromones in minnows
tactile, and auditory, and each category constitutes of exactly what you would think. Some animal communication can get very complex, such as the communication of worker bees to the hive of the exact position, amount, and quality of a food source.

Animals that communicate using odor or taste secrete chemicals called pheromones. Pheromones are usually associated with communication for reproductive purposes. They can also serve as warnings or alarms. For example, if certain catfish or minnows are injured, they will emit pheromones that make nearby fish more cautious, as well as group more closely together.

How development affects behavior:
Animals will perform all the above behaviors regardless of how they were raised. This is called innate behavior: development does not affect the behavior. Other behaviors can vary based on the animal's experience during growth. One way to test how a behavior is affected is by using a cross-fostering study: in this study a baby animal is put in the care of an animal of a different species, and the differences between that animal's behavior and one that was raised normally are compared. Since this study isn't really applicable to humans, a twin study is more fitting: the observation of differences in identical twins' behavior based on certain experiences. In both cases, development heavily influences behavior.

Learning:
One of the most powerful ways the environment affects behavior is through learning: the modification of behavior based on specific experiences.

One form of learning is called imprinting, which includes both learned and innate components. Imprinting is the formation at a specific stage of development of a behavioral response that usually lasts the whole animal's life. Imprinting is distinguishable from other types of learning because it has a sensitive period: there is a specific period of time when an animal can learn by imprinting. During this sensitive period, a young animal will be imprinted by its parents and their behaviors, and learn to try to copy them. Imprinting is obviously a type of learned behavior, but it is also somewhat of an innate behavior because birds for example will imprint whatever they see first, which might not necessarily be their actual mother.

Another form of learning is called spatial learning, where an organism learns to establish a memory of specific locations in the environment, such as nests, food sites, hazards, ect. Animals generally learn their environment by relating these sites to certain landmarks, but will also navigate using other senses like smell. Animals can also create a cognitive map, where they will relate positions of landmarks to each other in order to navigate to a certain site.

This blue jay has probably now associated the monarch's color and bad taste
This blue jay has probably now associated the monarch's color and bad taste

Another form of learning is associative learning, where animals will associate one environmental feature to another, usually across different senses. One example of associative learning is with a blue jay and a monarch butterfly. A young blue jay will eat a tasty looking monarch butterfly, but since this insect is poisonous, it will cause the blue jay to experience a very uncomfortable taste as well as vomiting. The blue jay will then associate the bright orange color of the butterfly with the foul taste and will keep itself from eating any insect bearing a close resemblance. Some animals can only associate certain senses, and that's just how they evolved.


Complex forms of learning involve a process called cognition: the process of knowing that involves awareness, reasoning, recollection, and judgement. People generally think primates and dolphins are the only animals smart enough to go through a cognitive process, but studies in laboratories show that even insects can perform such a complex learning method. Animals have also been shown to do problem solving, the devising of a method to bypass apparent or real obstacles. Problem solving is usually only done successfully by only the smartest animals, like the ones mentioned before, but one of the most notable examples is the advanced problem solving ability of ravens, one of the few animals that will create tools to help them accomplish a goal.
51_10HoneybeeMazeTest-L.jpg
In this example, honeybees learned in the color maze that choosing the same 2 colors in a row would get them a reward. When moved into a pattern maze, the bees chose the same 2 patterns in a row

The above learning methods and behaviors are developed relatively quickly. Some behaviors take a much longer time; for example, a bird learns to sing gradually and in different stages.Singing is learned by imprinting: the bird listens to the parents during the sensitive period, but doesn't start to actually sing yet. Instead it chirps in response to its own species' call. Then when the bird grows more, it will attempt the song, and fix errors. This is an example of a developed behavior.

Although some animals use the methods above, other animals can learn problem solving by observing groups of their species and seeing how they interact with one another. This is observation is called social learning. An example is a young monkey watching an older monkey crack a nut open with a stone, and then realizing that that's the best way to get to the food inside. Social learning forms culture, which is the system of information transfer via social learning that influences the behaviors of individuals in the population. Culture can influence the phenotypes and therefore the genetic fitness of the population.
51_13EvolFruitFlyForag-L.jpg
Optimal foraging model for foraging distances and population

How behavior enhances survival and reproductive success:
To survive, an animal needs food. Behavior that involves gathering and eating food is called foraging. Animals want to forage with minimum energy and maximum results. An example of how they modify behavior for this is in low populations, animals will forage at lower distances than at high populations, because they wouldn't need to move past areas of food depletion in low populations. This minimum energy maximum benefit behavior is described by an optimal foraging model.

Optimal foraging is useless if the forager gets eaten by a predator. This means that the animal must also balance risk and reward. This means that they have to evaluate the situation and forage as cautiously as possible without expending too much energy.


Survival doesn't mean anything either if the animal doesn't pass on their genes to the next generation. So the animal must also develop mating behaviors and choose the right mate to most efficiently reproduce. Mating behaviors include seeking or attracting mates, choosing potential mates, competing for mates, and caring for offspring. Different animals have different mating behaviors. Most animals are promiscuous, meaning that they don't bond or stay with a single mate. If the mates stay together for a longer period with a single mate, then they're called monogamous, and if they stay with multiple mates, they're polygamous. Most polygamous exhibit polygyny, which is when one male stays with multiple females, but some exhibit polyandry: when one female stays with multiple males. Most animals also exhibit sexual dimorphism, which is when the male and females appear different within the same species. Monogamous generally don't exhibit sexual dimorphism, while for polygamous animals the entire sex that wants to stay with a single animal of the opposite sex is usually more
Mate-choice copying
Mate-choice copying
ornamented and flashy. Another factor influencing mating behavior is certainty of paternity, where the male wants to make sure that his genes are the ones being passed on. This means that is the animal is in a group and has mated with a female, he will protect that female from other males trying to mate with it

Sexual Selection:
Sexual selection can be intersexual (members of one sex choosing mates of the other) or intrasexual (competition within a sex for mates). Mate choice will influence the evolution of the opposite sex, because certain traits will be chosen repeatedly. Some animals will undergo mate-choice copying, which is when the choice of mates will be copied by the choosers. For example, a certain female guppy usually chooses males with the brightest orange coloring. However, an experiment was conducted where a fake female was made to look like it was courting with a male with lesser orange coloration. The other females then started to choose the males with less orange coloring.

Competition between males is usually physical, and can contain agnostic behavior, which is a sort of ritual to gain a mate.

Game Theory
The fitness of a particular behavior is often determined by other behaviors. Game theory is the evaluation of alternative strategies in situations where every individual's strategy is involved to determine the outcome. An example is when an animal that isn't very physical and wouldn't win competitions changes its strategy to a 'sneaky' mating strategy. Instead of competing physically, the sneaky male might quickly mate when the other males are battling. Then the sneaky genes will be passed on and the behavior continued.

Evolution of behavior
Most closely related species exhibit similar behaviors, suggesting that behavior is genetic. So how did strange behaviors that don't look like they benefit the animal evolve? An example of such behavior is altruism. Altruism is when an animal lowers its own fitness, but increases fitness of others in the population. How would selfless behavior remain in the gene pool if they have decreased fitness? This is easily explainable with parents helping offspring, because it keeps their offspring and thus their genes from dying off from the gene pool. If its not a parent helping an offspring, the animals are practicing inclusive fitness, because by helping siblings within their pack or parents, they will increase the chances of some of their genes passing on because they share some genes with siblings. Inclusive fitness can be explained by Hamilton's rule: rB > C, where r is the coefficient of relatedness, C is cost, and B is benefit. Natural selection that favors altruistic behavior by enhancing reproductive success of relatives is called kin selection.

In humans:
Human culture is related to evolution in sociobiology. The main idea of this practice is that behaviors exist because they are expressions of genes that were favored by natural selection. Human behavior is a very vast and still expanding field; we don't yet know all of it.

Click here to return to Ecology home page
Return to Ecology home