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Animal behavior is the set of actions or reactions that organisms display in response to internal or external stimuli. Organisms respond to both internal conditions (like hormone levels or hunger) and external cues (like predators or temperature). These responses may be behavioral (e.g., hiding in shade) or physiological (e.g., sweating or shivering).
These behaviors are often vital to survival and reproduction, and like any other trait, behavior is a phenotype that can be shaped by evolution. It is influenced by both genetic programming and environmental experience. As a phenotype, behavior can be selected for by natural selection if it improves an organism's ability to survive and reproduce.
For example, in stickleback fish, males instinctively attack anything with a red belly during breeding season. This innate behavior is encoded genetically and helps defend territory and nesting sites - key to reproductive success. This behavior is an example of a fixed action pattern - an instinctual sequence of behaviors that once started, will continue to completion.
Innate Behaviors
Innate Behaviors
Innate behaviors are genetically hardwired. They are performed correctly without prior experience or learning. For example, turtle hatchlings instinctively move toward the ocean immediately after hatching.
Learned Behaviors
Learned Behaviors
Learned behaviors are shaped by experience. They allow flexibility and can help organisms adapt to changing environments. As an example, crows have learned how to use tools to access food or solving multi-step puzzles.
Many animals show a mix of both. For instance, songbirds have an innate ability to sing, but they learn their species’ specific song by listening to adults.
When studying behavior, there are typically two main questions that scientists ask:
What is the proximate cause of this behavior? In other words, what stimulus immediately led to this behavior occuring.
What is the ultimate cause of this behavior? In other words, why did this behavior evolve?
Organisms often respond to stimuli with movement, and there are two main types:
Kinesis
Kinesis
Kinesis is a non-directional response to a stimulus. The organism moves more or less, but not toward or away from the stimulus.
Taxis
Taxis
Taxis is a directional response to a stimulus. For example, moths exhibit positive phototaxis and fly toward light sources.
Communication and Signaling
Communication and Signaling
Animals use various types of signals to communicate. These signals cause changes in the behavior of other organisms and can influence reproductive success, dominance, or resource acquisition.
Types of Signals and Examples:
Visual – Fireflies flash specific light patterns to attract mates.
Auditory – Male frogs use croaks to signal territory and attract females.
Tactile – Honeybees use the waggle dance to physically show other bees the direction and distance to a food source.
Chemical – Ants leave pheromone trails to guide others to food.
Electrical – Some fish, like electric eels, use electric fields to locate prey or communicate.
These signals help animals to find mates, establish territory, signal dominance, avoid danger, cooperate in hunting, and more.
Even unicellular organisms can exhibit behaviors. In quorum sensing, bacteria release signaling molecules into the environment. As the population grows, these molecules increase in concentration. Once a threshold is reached, the bacteria collectively change their behavior. In Vibrio fischeri, quorum sensing activates bioluminescence only when enough bacteria are present. In pathogenic bacteria, quorum sensing can trigger the expression of virulence genes when population density is high enough to launch a successful infection.
Cooperative Behavior
Cooperative Behavior
Even unicellular organisms can exhibit behaviors. In quorum sensing, bacteria release signaling molecules into the environment. As the population grows, these molecules increase in concentration. Once a threshold is reached, the bacteria collectively change their behavior. In Vibrio fischeri, quorum sensing activates bioluminescence only when enough bacteria are present. In pathogenic bacteria, quorum sensing can trigger the expression of virulence genes when population density is high enough to launch a successful infection.
Sometimes, animals work together in ways that increase the fitness of the individual and the group.
Meerkats take turns keeping watch for predators, even though it puts the lookout at risk.
Bees and ants sacrifice their own reproduction to support the queen.
Pack hunting in African wild dogs increases hunting success for everyone involved.
One of the most fascinating examples comes from naked mole rats. These mammals live in underground colonies with a eusocial structure, similar to that of bees. Each colony has a single breeding queen, a few breeding males, and many sterile workers. The workers perform tasks like tunnel maintenance, food gathering, and defending the colony. Some individuals even have the exclusive job of eating a lot and then using their bigger bodies to plug the tunnel holes when it rains! Even though most individuals never reproduce, they increase their inclusive fitness by supporting close relatives, ensuring that shared genes are passed on.
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