Appetitive behavior serves as the evolutionary engine of animal and human survival, orchestrating the complex sequence of actions that bring an organism into direct contact with essential biological goals. From foraging across vast terrains to seeking social intimacy, this active motivational phase bridges internal physiological deficits with the external stimuli necessary for homeostasis. Understanding the neurobiological, ethological, and psychological dimensions of appetitive behavior reveals how anticipation, incentive salience, and goal-directed learning shape the behavioral repertoire of living organisms.
Appetitive Behavior
1. Concise Definition
Appetitive behavior refers to the initial, flexible, and goal-oriented phase of motivated behavior directed toward discovering, approaching, and securing an unconditioned stimulus or reward. Unlike the rigid consummatory actions that conclude an instinctual sequence, appetitive behavior is characterized by high behavioral plasticity, environmental exploration, and sensitivity to instrumental learning. In contemporary neuroscience and behavioral psychology, it represents the operational manifestation of “wanting”—the neurochemical and cognitive mobilization toward an anticipated reinforcement.
This behavioral sequence begins when an internal state of deprivation or an external sensory cue initiates seeking activities. Through exploratory locomotion, sensory scanning, and learned approach strategies, the organism navigates its habitat to locate the desired incentive, such as food, water, a receptive mate, or thermal shelter. Once the target stimulus is reached and sensory contact is established, appetitive behavior transitions into the stereotyped, reflexive actions that constitute the consummatory phase.
Beyond basic biological drives, the concept encompasses complex human pursuits, including economic striving, substance-seeking behaviors in addiction, and novelty seeking. It reflects an organism’s continuous calculation of cost-benefit ratios, reward probabilities, and energetic investments, making it a foundational paradigm for understanding motivational neurobiology, ethology, and psychiatric pathology.
2. Etymology & Linguistic Origin
The term appetitive traces its etymological lineage to the Latin verb appetere, compounded from the prefix ad- (meaning “to,” “toward,” or “at”) and petere (meaning “to seek,” “strive after,” “attack,” or “aim for”). The post-classical Latin derivative appetitivus entered Middle English and Early Modern philosophical discourse through Scholastic adaptations of Aristotelian psychology, denoting an intrinsic faculty or power of the soul oriented toward pursuing perceived goods and avoiding perceived evils.
In classical philosophy, Aristotle distinguished the vegetative, appetitive (orektikon), and rational faculties of the psyche. The appetitive soul represented the seat of desires, passions, and motor inclinations that responded to sensory representations. Thomas Aquinas preserved this taxonomy in medieval philosophy, classifying appetites into natural, concupiscible, and irascible drives that move the animate being toward life-sustaining objects.
The modern scientific adoption of the phrase “appetitive behavior” occurred during the early twentieth century within the emerging discipline of ethology. Wallace Craig formally introduced the distinction between “appetitive behavior” and “consummatory action” in his seminal 1918 paper, liberating the term from metaphysical connotations and grounding it in objective, empirical observations of animal drive states and behavioral sequences.
3. Pronunciation & Grammatical Form
The term is pronounced phonetically in American English as /əˈpɛtɪtɪv bɪˈheɪvjər/ and in Received Pronunciation British English as /ˈæpɪtɪtɪv bɪˈheɪvjə/. Primary lexical stress in “appetitive” falls on either the second syllable (/əˈpɛt-/) or the first syllable (/ˈæp-/), depending on regional academic dialects, with the secondary stress resting on the antepenultimate or penultimate syllable.
Grammatically, “appetitive” functions as a classifying and qualitative adjective modifying the non-count or count noun “behavior.” In psychometric and psychological contexts, it frequently enters into compound noun phrases such as appetitive conditioning, appetitive motivation, appetitive phase, and appetitive aggression. The nominal form directly referencing the psychological state is appetite, while the opposite valence is grammatically designated by the adjective aversive, yielding the canonical motivational dichotomy of appetitive versus aversive systems.
4. Detailed Conceptual Explanation
Appetitive behavior constitutes the dynamic operational phase that enables an organism to bridge the spatial, temporal, and energetic gap separating its current state from a biological imperative. Living systems require continuous thermodynamic inputs and periodic reproductive encounters to maintain biological integrity and pass on genetic material. Because these resources are rarely distributed uniformly within any natural environment, organisms cannot rely solely on passive waiting or stationary consumption. Appetitive behavior encompasses the entire repertoire of proactive movements, cognitive mapping, sniffing, scanning, and habitat traversal mobilized to locate valuable resources.
A critical characteristic of appetitive behavior is its remarkable behavioral plasticity and structural variability. When an animal experiences energy depletion, it does not engage in a static, pre-programmed routine; instead, it initiates an open-ended search that adapts to ambient conditions, historical learning, topographical obstacles, and current predator risks. A wolf hunting for prey may alternate between tracking scents, sprinting across open fields, stalking through dense foliage, and waiting in ambush. Every component of this hunt represents appetitive behavior, each step modulated by moment-to-moment feedback from the environment. This adaptability contrasts sharply with the consummatory phase, which is marked by species-typical, invariant motor patterns such as mastication, deglutition, or copulatory reflexes.
At the neurobiological level, appetitive behavior is governed predominantly by ascending mesolimbic and mesocortical dopamine pathways. Projections arising from the ventral tegmental area (VTA) and innervating the nucleus accumbens, amygdala, and prefrontal cortex do not primarily encode the sensory pleasure of receiving a reward; rather, they mediate incentive salience, anticipation, and the energetic mobilization necessary to obtain that reward. When an organism detects a cue associated with food, a burst of phasic dopamine release transforms the neutral mental representation into an attractive, “wanted” goal, compelling the animal to initiate appetitive approach behavior.
Furthermore, appetitive behavior operates under hierarchical neuroendocrine control. Hypothalamic nuclei—most notably the lateral hypothalamus and the arcuate nucleus—monitor circulating energy markers such as leptin, insulin, and ghrelin. When ghrelin levels rise during fasting, it activates neuropeptide Y (NPY) and agouti-related peptide (AgRP) neurons, which in turn project to the mesolimbic dopamine system. This homeostatic signal lowers the behavioral activation threshold, transforming the animal from a state of quiet rest into one of vigorous appetitive exploration. The organism becomes hyper-responsive to sensory cues that predict nourishment, illustrating how systemic physiological deficits are translated into observable motor drive.
Finally, appetitive behavior encompasses distinct temporal phases, beginning with general, cue-independent search behavior (sometimes termed “undirected search”) and culminating in focused, cue-guided approach (termed “directed search”). As the organism approaches the reward, its behavioral repertoire narrows. Cognitive evaluations transition from broad environmental scanning toward fine-motor execution, bringing the incentive stimulus within direct physical reach so that consummatory reflexes can take over.
5. Historical Development
The systematic study of appetitive behavior originated within comparative psychology and classical ethology during the early twentieth century. Prior to this period, animal behavior was predominantly interpreted through the lens of pure Cartesian mechanical reflexology or anthropomorphic introspection. In 1918, American ethologist Wallace Craig published a landmark paper titled “Appetites and Aversions as Constituents of Instincts” in the Biological Bulletin. Craig proposed that an instinct is not a single, monolithic reflex chain, but a dynamic sequence composed of an appetitive phase driven by an internal state of unrest, leading to a state of satisfaction achieved through a consummatory reaction.
Craig’s operational dichotomy was enthusiastically adopted and formalized by European ethologists Konrad Lorenz and Nikolaas Tinbergen during the 1930s and 1940s. Lorenz integrated appetitive behavior into his famous psycho-hydraulic model of motivation, arguing that endogenous “action-specific energy” accumulates over time, driving appetitive searching until a specific innate releasing mechanism (IRM) encounters a sign stimulus, triggering a stereotypic fixed action pattern (FAP). Tinbergen expanded this concept in The Study of Instinct (1951), arranging appetitive behaviors into hierarchical levels that descend from broad appetitive impulses (e.g., reproduction) down to localized, precise motor coordinates (e.g., territory defense, nest-building, and courtship).
During the mid-twentieth century, the behaviorist tradition in North American experimental psychology approached appetitive phenomena through instrumental and operant conditioning paradigms. B. F. Skinner and Clark Hull operationalized appetitive behaviors as learned lever-presses and maze-running patterns sustained by primary and secondary reinforcers. In Hull’s drive-reduction theory, appetitive seeking was viewed as an instrumental response energized by non-specific biological drive states and guided by habit hierarchies.
The modern era began in the late 1980s and 1990s with the cognitive and affective neuroscience revolution. Researchers such as Kent Berridge and Terry Robinson challenged the long-held assumption that motivation and pleasure are identical neurobiological processes. By dissecting the brain circuitry of reward, they demonstrated that “wanting” (appetitive incentive salience, driven by dopamine) is neurochemically and anatomically dissociable from “liking” (consummatory pleasure, mediated by endogenous opioid and cannabinoid hot spots). This insight transformed contemporary research on addiction, eating disorders, and neuroeconomics, establishing appetitive behavior as an independent domain of investigation.
6. Theoretical Foundations
Several theoretical frameworks explain how appetitive behaviors are organized, initiated, and regulated:
Ethological Hierarchy Theory: Developed by Tinbergen and Lorenz, this model posits that motivational systems are structured hierarchically. At the highest level, generalized appetitive drives mobilize broad classes of behavior. As the animal moves closer to its goal, the appetitive sequences become increasingly restricted and specialized, driven by environmental feedback and releasing mechanisms, until the system discharges through a consummatory act, resetting the motivational pressure.
Incentive Salience Theory: Formulated by Berridge and Robinson, this neuropsychological framework divides reward into three distinct psychological components: learning (associative representations), “liking” (hedonic impact), and “wanting” (incentive salience). Appetitive behavior is the direct behavioral consequence of incentive salience. Dopaminergic pathways imbue neutral mental representations and perceptual stimuli with motivational attraction, transforming mere perceptual cues into compelling incentive magnets that drive vigorous approach and seeking behaviors.
Behavioral Activation and Approach Systems (BAS): In human personality and cognitive neuroscience, Jeffrey Gray’s Reinforcement Sensitivity Theory conceptualizes appetitive behavior through the Behavioral Approach System (BAS). The BAS is a hypothesized neurobehavioral engine sensitive to signals of reward, conditioned appetitive stimuli, and escape from punishment. Individual differences in the sensitivity of this system account for variations in trait impulsivity, reward responsiveness, and positive affectivity across populations.
Optimal Foraging Theory: Grounded in evolutionary ecology, this model evaluates appetitive behavior through economic optimization. Organisms must balance the energetic costs and predation risks of searching for sustenance against the caloric gain of the food item. Natural selection favors appetitive strategies that maximize the net rate of energy gain per unit of foraging time, providing a computational basis for the variable search patterns observed in nature.
7. Key Components, Types & Dimensions
Appetitive behavior can be deconstructed into several distinct structural components, subtypes, and operational dimensions:
- Undirected (General) Search Behavior: The preliminary stage characterized by spontaneous, broad exploratory locomotion and sensory surveillance in the absence of explicit, proximate reward cues.
- Directed (Focal) Search Behavior: The targeted phase initiated once a predictive sensory cue or spatial trail is detected, during which the organism narrows its motor path directly toward the reinforcement.
- Incentive Salience (“Wanting”): The psychological and neurochemical attribution of motivational value to a stimulus, driving subjective desire and objective physical approach.
- Instrumental Conditioning and Effort Exertion: The expenditure of physical and cognitive labor (e.g., lever pressing, traversing obstacles, solving spatial puzzles) to bring the reward within reach.
- Appetitive Aggression: A specialized subtype wherein predatory or aggressive actions are experienced as intrinsically motivating and reinforcing rather than aversively defensive.
- Appetitive Proceptivity: The preparatory courtship displays, signaling behaviors, and active solicitations performed to attract and secure a willing reproductive partner.
- Anticipatory Arousal: Autonomic and central nervous system activation—manifested as increased heart rate, pupil dilation, and vigilance—preparing the body for engagement with the anticipated incentive.
8. Examples & Illustrative Cases
To grasp the practical manifestation of appetitive behavior across species, consider the classic hunting sequence of the domestic cat (Felis catus). When a cat experiences predatory motivation, it does not immediately pounce. Instead, it engages in extensive appetitive behaviors: stealthy territorial patrolling, pausing to sniff olfactory markings, positioning its ears toward faint rustling sounds, and entering a slow, calculated stalking posture. Each of these steps is flexible and dependent on real-time sensory feedback. Only when the cat leaps, pins, bites, and ingests the rodent does it cross the threshold into consummatory behavior. If the prey scurries under a floorboard, the cat remains frozen in appetitive vigilance or resumes searching, demonstrating the resilience of the appetitive drive.
A parallel illustration from human psychopathology appears in substance use disorders. Consider an individual struggling with severe opioid addiction. The multi-hour process of securing financial resources, sending text messages, driving across a city to meet a supplier, negotiating the transaction, and preparing the injection equipment constitutes an intense, all-consuming sequence of appetitive behavior. Dopamine levels in the striatum surge during this anticipatory period, frequently peaking immediately before the drug is administered. The actual biochemical intoxication and transient relief represent the consummatory endpoint, but the appetitive seeking is what dominates the patient’s daily functional life and leads to significant functional impairment.
In everyday human life, appetitive behavior is evident in modern culinary culture. Browsing restaurant menus online, smelling food aromas wafting from a kitchen, reading food reviews, and walking to a bakery represent appetitive actions. These actions are accompanied by autonomic shifts, including cephalic-phase insulin release and salivation, readying the digestive tract for the consummatory acts of mastication and swallowing.
9. Measurement & Assessment
Measuring appetitive behavior requires paradigms that isolate the motivational, anticipatory, and effort-related components of a behavioral sequence from the consummatory act itself:
Operant Progressive Ratio (PR) Schedules: In preclinical neurobiology, rodents are placed in operant conditioning chambers where each successive delivery of a food pellet or intravenous drug infusion requires an increasing number of lever presses or nose pokes (e.g., 1, 2, 4, 9, 16, 25…). The “breakpoint”—the maximum effort the animal will expend before abandoning the task—provides an objective quantitative index of appetitive motivation and reward valuation.
Effort-Related Choice Paradigms: Developed by John Salamone and colleagues, paradigms such as the Concurrent Choice Task present an animal with an option between a low-effort, low-reward option (freely available standard chow) and a high-effort, high-reward option (barrier jumping or intensive lever pressing for high-fat sucrose pellets). Dopamine depletion in the nucleus accumbens reliably impairs the animal’s willingness to engage in the high-effort appetitive search without diminishing its consummatory consumption of freely available food.
Conditioned Place Preference (CPP): This behavioral assay tests an animal’s preference for an environment previously paired with an appetitive stimulus versus a neutral environment. The time spent navigating the reward-paired chamber in a drug-free, unreinforced state serves as a metric of conditioned appetitive approach.
Psychometric Self-Report Scales: In human psychological research, appetitive tendencies are quantified using standardized psychometric instruments. The Carver and White BIS/BAS Scales assess individual differences in the sensitivity of the Behavioral Approach System across three subscales: Drive, Reward Responsiveness, and Fun Seeking. The Appetitive Aggression Scale (AAS) measures the extent to which individuals perceive violent acts as fascinating, rewarding, and exciting.
Neuroimaging and Eye-Tracking: Human laboratory studies employ functional Magnetic Resonance Imaging (fMRI) paired with the Monetary Incentive Delay (MID) task to measure blood-oxygen-level-dependent (BOLD) responses in the ventral striatum during the anticipation of reward. Eye-tracking paradigms assess appetitive attentional bias by measuring gaze fixation duration on appetitive cues, such as ultra-processed foods or substance-related paraphernalia.
10. Applications & Practical Significance
Understanding appetitive behavior is essential for addressing clinical, behavioral, and societal challenges:
Addiction Psychiatry: Substance use disorders are increasingly conceptualized as pathologies of appetitive dysregulation. Chronic drug exposure induces neuroadaptations in the mesolimbic circuitry, sensitizing the incentive salience attributed to drug-associated cues. Consequently, individuals experience compulsive appetitive craving even after prolonged abstinence, making appetitive seeking a central target for behavioral extinction and pharmacotherapies.
Metabolic Disorders and Obesity: The modern food environment is saturated with hyper-palatable, energy-dense foods and pervasive advertising cues. Many individuals struggle with “hedonic hunger”—an overactive appetitive drive to seek food in the complete absence of metabolic energy deficits. Interventions targeting cue-induced craving, mindful awareness of appetitive impulses, and modern GLP-1 receptor agonists (which dampen both peripheral hunger and central appetitive valuation) illustrate the medical relevance of modulating this phase.
Animal Welfare and Veterinary Science: Confined livestock and captive zoo animals often display severe behavioral pathologies, such as stereotypic pacing or self-mutilation, when their appetitive foraging drives are frustrated. Modern animal welfare emphasizes “environmental enrichment”—such as scatter feeding, puzzle feeders, and naturalistic foraging grounds—which permits animals to engage in healthy, natural appetitive sequences rather than simply receiving passive meals.
Neuromarketing and User-Experience Design: Commercial enterprises leverage appetitive psychology to design engaging digital interfaces and marketing campaigns. The deployment of intermittent reward schedules, notification chimes, and infinite scrolling on social media platforms taps directly into the dopamine-driven appetitive seeking cycle, compelling users to continuously refresh their feeds in pursuit of novel social reinforcement.
11. Research & Empirical Evidence
Decades of empirical research have mapped the physiological and neural architecture governing appetitive behavior. A transformative milestone occurred in 1954, when James Olds and Peter Milner discovered that rats with electrodes implanted in the septal area and lateral hypothalamus would repeatedly press a lever thousands of times per hour to receive direct electrical stimulation. This demonstrated the existence of dedicated neural substrates dedicated to reinforcement and appetitive seeking.
Subsequent work by Wolfram Schultz in the 1990s revolutionized reward theory by identifying the electrophysiological firing properties of dopamine neurons. Using single-unit recordings in non-human primates, Schultz demonstrated that dopamine neurons fire in response to unpredictable rewards. Crucially, as the animals learned that a sensory cue preceded the reward, dopamine firing shifted entirely from the reward itself to the conditioned cue. The dopamine surge was shown to encode a “reward prediction error,” signaling the discrepancy between expected and received outcomes. This confirmed that dopamine acts as an anticipatory signal driving appetitive engagement rather than a readout of hedonic consumption.
Kent Berridge and colleagues validated this dissociation experimentally through the taste reactivity test. By administering neurotoxins to deplete striatal dopamine in rodents, they observed that the animals stopped seeking food and would starve if not tube-fed (a loss of appetitive behavior). Yet, when sugar solutions were placed directly into their mouths, these dopamine-deficient animals exhibited the exact same facial expressions of hedonic pleasure (“liking”) as healthy controls. Conversely, microinjections of opioids into localized hedonic hot spots in the nucleus accumbens enhanced consummatory pleasure without necessarily increasing appetitive lever pressing, cementing the mechanistic boundary between “wanting” and “liking.”
More recently, optogenetic and chemogenetic studies have isolated the precise neuronal populations controlling appetitive states. Research out of Scott Sternson’s laboratory demonstrated that activating AgRP neurons in the arcuate nucleus of sated mice triggers intense appetitive food-seeking behavior within minutes. These investigations demonstrate that specific genetic and molecular switches within the brain directly regulate the transition from quiescence to vigorous appetitive seeking.
12. Cultural & Cross-Cultural Considerations
While the fundamental neurobiology of appetitive behavior is universal across humanity, its behavioral expressions, regulatory controls, and cognitive appraisals are heavily shaped by cultural systems. Different societies establish distinct norms regarding which appetitive drives are encouraged, channeled, or suppressed.
In Western consumerist cultures, individual appetitive seeking is frequently valorized through ideals of personal ambition, entrepreneurial drive, material acquisition, and romantic pursuit. Economic and social architectures reinforce persistent appetitive striving, framing the continuous seeking of higher status, wealth, and novelty as a personal virtue. Conversely, several Eastern philosophical and religious traditions, such as Buddhism, Daoism, and classical Stoicism, conceptualize uncontrolled appetitive desire (taṇhā or excessive striving) as the fundamental source of human suffering. These frameworks cultivate cultural practices, such as mindfulness, fasting, and monastic contemplation, designed to systematically dampen appetitive reactivity and promote homeostatic equanimity.
Cultural definitions also govern what constitutes an acceptable target for appetitive drive. For example, culinary traditions dictate which sensory items are classified as appetizing incentives versus aversive objects. Similarly, courtship rituals vary across societies, dictating whether appetitive romantic seeking must be highly indirect, formalized, and mediated by community elders, or direct, informal, and individualistic. These variations show that cultural conditioning acts as a top-down regulator, determining the legitimate channels through which human appetitive motivation is expressed.
13. Criticisms, Debates & Limitations
Despite its widespread utility, the conceptual division between appetitive and consummatory behavior has sparked theoretical controversies within psychology and neuroscience:
The Blurring of Behavioral Boundaries: Some contemporary ethologists and motor physiologists argue that the distinction between appetitive and consummatory behavior is an oversimplification. In natural environments, behavioral sequences are nested rather than linear. For example, when a predator chases prey, each step, sprint, turn, and lunge contains elements of both motor execution (stereotypic actions) and open-loop search. Dividing these complex, continuous behaviors into two rigid categories can lead to artificial dichotomies that obscure the integrated nature of motor control.
Reductionist Dopamine Models: An ongoing debate involves the precise cognitive interpretation of dopamine’s role in appetitive behavior. While the incentive salience hypothesis remains widely influential, competing theorists argue that dopamine encodes sensorimotor energization, precision optimization, or formal Bayesian prediction errors rather than psychological “wanting.” Over-attributing all appetitive seeking to mesolimbic dopamine risks neglecting the vital roles of glutamate, serotonin, acetylcholine, and hypothalamic neuropeptide systems.
Ethical Concerns in Appetitive Aggression Research: The application of appetitive behavior models to human violence, particularly through the concept of “appetitive aggression” among combatants and gang members, has sparked controversy. Some sociologists and human rights scholars caution that describing violent acts as neurobiologically reinforcing or appetitive may be misinterpreted as legitimizing war crimes or reducing systemic geopolitical violence to biological instincts.
14. Related Terms & Distinctions
To prevent conceptual confusion, appetitive behavior must be distinguished from several closely related psychological constructs:
- Consummatory Behavior: The concluding, highly stereotypic, and reflexive phase of a motivational sequence (e.g., chewing, swallowing, ejaculation) that directly satisfies a biological drive. Appetitive behavior is variable, exploratory, and preparatory; consummatory behavior is fixed, responsive, and definitive.
- Incentive Salience: The neurochemical attribution of motivational “magnetism” to a perceptual stimulus, mediated by dopamine. While incentive salience is the underlying neurocognitive process, appetitive behavior is its observable motor and behavioral manifestation.
- Aversive Behavior: Behaviors organized around avoiding, escaping, or defending against noxious, dangerous, or painful stimuli. Appetitive behavior is valenced positively (approach), whereas aversive behavior is valenced negatively (avoidance).
- Satiety: The post-consummatory physiological and psychological state characterized by the absence of appetitive drive and the cessation of seeking behaviors.
- Goal-Directed Action: A cognitive framework where behavior is guided by an explicit knowledge of the contingency between an action and its outcome, as well as the current value of that outcome. While much appetitive behavior begins as goal-directed, extended repetition can cause it to transition into an autonomous habit.
15. Summary / Key Takeaways
Appetitive behavior is the essential exploratory, flexible, and approach-oriented phase of motivated action that enables organisms to locate and secure vital biological resources. Initiated by internal physiological signals and triggered by environmental reward cues, it is characterized by behavioral plasticity, instrumental effort, and anticipatory arousal. Neurobiologically driven by mesolimbic dopamine networks and incentive salience mechanisms, appetitive behavior is distinct from the stereotyped, reflexive consummatory actions that conclude an instinctual cycle.
From animal foraging to human consumer choices, appetitive behavior governs how living beings interact with opportunities in their environments. When dysregulated, it contributes to major psychological and metabolic disorders, including addiction, obesity, and pathological gambling. Understanding its neurobiology, historical development, and clinical applications provides vital insight into how desire, anticipation, and goal-directed action shape the natural and human world.
References
- Berridge, K. C., & Robinson, T. E. (1998). What is the role of dopamine in reward: Hedonic impact, reward learning, or incentive salience? Brain Research Reviews, 28(3), 309–369. https://doi.org/10.1016/S0165-0173(98)00019-8
- Craig, W. (1918). Appetites and aversions as constituents of instincts. Biological Bulletin, 34(2), 91–107. https://doi.org/10.2307/1536346
- Lorenz, K. (1950). The comparative method in studying innate behaviour patterns. Symposia of the Society for Experimental Biology, 4, 221–268.
- Salamone, J. D., & Correa, M. (2012). The mysterious motivational functions of mesolimbic dopamine. Neuron, 76(3), 470–485. https://doi.org/10.1016/j.neuron.2012.10.021
- Tinbergen, N. (1951). The Study of Instinct. Oxford University Press.