Territoriality

The scientific study of territoriality traces its origins to the early twentieth century. H. Eliot Howard's 1920 monograph Territory in Bird Life provided the first systematic treatment, arguing that male songbirds defend discrete areas to attract mates and secure nesting sites. Margaret Morse Nice (1941) subsequently published a landmark review, 'The role of territory in bird life,' which catalogued the diversity of territorial systems in birds and helped standardize terminology. Gladwyn Kingsley Noble (1939) offered a deliberately minimal definition—territory as 'any defended area'—which became widely adopted because of its inclusivity across taxa. William Henry Burt (1943) later drew the critical distinction between a 'territory' (a defended area) and a 'home range' (the larger area traversed during normal activities), a conceptual separation that remains foundational in behavioral ecology.

Jerram L. Brown (1964) transformed the study of territoriality by introducing the concept of economic defendability. Brown proposed that an animal should become territorial only when the benefits of exclusive resource access exceed the costs of defense—a principle later extended by Brown and Orians (1970) to spacing patterns more broadly. Under this framework, the optimal territory size is the one that maximizes the net energy gain (or fitness) after subtracting defense costs. Several factors modulate the cost-benefit balance. Resource density and predictability are key: when resources are concentrated and their locations are stable and foreseeable, defense becomes economically feasible, whereas widely dispersed or unpredictable resources make territorial defense unprofitable. Intruder pressure also matters; as the number of potential competitors increases, the marginal cost of defending each additional confrontation rises, eventually making defense uneconomical. Thomas Schoener (1983) reconciled competing models of optimal feeding-territory size and showed that the predicted territory size depends strongly on how food density and intruder rate interact.

Animals employ a diverse suite of mechanisms to establish and maintain territories. Olfactory signaling, particularly scent-marking, is widespread among mammals. Giuggioli, Potts, and Harris (2011) developed a mechanistic model demonstrating that the key parameters controlling territory formation in scent-marking animals are the average territory size (inversely proportional to population density) and the active scent time—the duration during which a deposited scent mark remains detectable and effective. Because an animal cannot permanently monitor all its borders, it must regularly traverse its territory to refresh scent marks before they fade, and the area it can defend is therefore limited by the time required for such boundary patrols. In their study of urban red foxes (Vulpes vulpes) in Bristol, the active scent time was estimated at approximately three to four days.

Vocal signals are the primary defense mechanism in many bird species. Male songbirds broadcast territorial songs that serve the dual purpose of repelling rival males and attracting females. Ritualistic visual displays—including posturing, color-patch exposure, and crest or frill erection—are employed by a wide range of taxa from fish to reptiles. Direct physical combat, though energetically costly and potentially injurious, serves as an escalated defense when signaling alone fails to deter intruders.

Territories can be classified according to the resources they protect and the extent of defense. Nice (1941) proposed a classification system for bird territories that remains influential. Type A territories encompass the entire home range and serve mating, nesting, and feeding functions simultaneously. Type B territories include a mating and nesting area but exclude the feeding range. Type C territories are defended only as small areas around the nest. Type D territories consist solely of a mating or display site (such as a lek). These categories have been broadly adapted for non-avian taxa, though the diversity of territorial systems across the animal kingdom defies any single classification.

The late twentieth and early twenty-first centuries saw the development of mechanistic models that derive territory patterns from the 'microscopic' behavior of individual animals. Lewis and Murray (1993) pioneered this approach with one-dimensional advection-diffusion equations based on the scent-marking behavior of gray wolves (Canis lupus) in Minnesota. Their models predicted the spontaneous formation of territory boundaries and buffer zones—areas between territories where neither pack ventures—that corresponded closely to observed field patterns. Later two-dimensional extensions (Moorcroft, Lewis, and Crabtree 2006) incorporated topography and prey distribution and were successfully tested against coyote (Canis latrans) territory data in Yellowstone.

The individual-based model (IBM) approach introduced by Giuggioli, Potts, and Harris (2011) provided complementary insights, revealing that territory boundaries are inherently dynamic and undergo slow subdiffusive movement—a feature not captured by continuum models. This framework demonstrated that territories function as deformable 'elastic objects' whose collective dynamics are governed by exclusion processes analogous to those in statistical physics.

Game-theoretic approaches have also been important. Maynard Smith and Price (1973) introduced the Hawk-Dove game, from which the 'Bourgeois' strategy (fight as owner, retreat as intruder) emerged as an evolutionarily stable strategy explaining the widespread respect for ownership observed in nature. Hinsch and Komdeur (2017) proposed a useful classification of territorial conflicts into three types: competition for entire territories (takeover), competition for space (boundary negotiation between neighbors), and competition for resources (intrusions for theft). Each type involves distinct cost-benefit structures and information asymmetries, and the authors argued that much inconsistency in the theoretical literature arises from conflating these distinct conflict types.

Territoriality is one of the most frequently invoked behavioral concepts in dinosaur paleobiology, though direct evidence is inevitably limited by the nature of the fossil record. Inferences about dinosaur territorial behavior rely on several lines of evidence.

The extant phylogenetic bracket (Witmer 1995) provides the first line of reasoning. Both extant groups bracketing non-avian dinosaurs—crocodilians and birds—are frequently territorial. Male crocodilians defend stretches of waterway, using bellowing displays and physical combat; birds exhibit some of the most elaborate territorial signaling known in the animal kingdom. Because territoriality is present in both outgroups, it is parsimoniously inferred to have been present in at least some non-avian dinosaurs.

Osteological evidence of intraspecific combat constitutes the second major line of evidence. Farke, Wolff, and Tanke (2009) conducted a statistical analysis of cranial lesions (periosteal reactive bone and healing fractures) in Triceratops and Centrosaurus, finding that Triceratops had significantly higher rates of lesions on the squamosal bone of the frill (P = 0.002) compared to Centrosaurus. This pattern is consistent with horn-to-horn combat in Triceratops—a behavior analogous to territorial or dominance contests in modern horned ungulates. In tyrannosaurs, facial bite marks on skulls and jaws provide evidence for intraspecific agonistic interactions. Peterson et al. (2009) documented face biting in a juvenile tyrannosaurid and suggested it could reflect play fighting or dominance establishment. Bell and Currie (2009) described a tyrannosaur jaw bitten by a confamilial, providing strong evidence for aggressive interactions that may have included territorial disputes.

Elaborate display structures such as the cranial crests of hadrosaurs, the horns and frills of ceratopsians, and the head crests of theropods like oviraptorosaurs are widely interpreted as having served communicative functions. In modern animals, such structures are often associated with territorial signaling and mate attraction, and an analogous function in dinosaurs is widely accepted.

Trace fossil evidence, including trackways showing parallel movement patterns and site fidelity, provides indirect behavioral data. Bonebeds of monospecific assemblages (e.g., Centrosaurus or Maiasaura) suggest gregarious behavior that in modern taxa is often associated with complex social and territorial dynamics.

Territoriality has far-reaching ecological consequences. By spacing individuals across the landscape, it regulates local population density and can prevent overexploitation of resources—a phenomenon sometimes described as the 'territorial buffer.' Territorial exclusion creates a class of non-territorial 'floaters' that may suffer reduced survival and reproductive success. Buffer zones between territories can serve as ecological refugia; in wolf-deer systems, white-tailed deer densities are notably elevated in the buffer zones between wolf pack territories where predation pressure is reduced.

Territoriality also influences disease dynamics. In territorial populations, the limited spatial overlap between individuals can slow pathogen transmission. However, disruption of territorial structures—for example, through population culling—can paradoxically increase disease spread by triggering territory rearrangement and elevated contact rates among displaced animals, as shown in studies of mange in red fox populations (Potts, Harris, and Giuggioli 2013) and bovine tuberculosis in badger populations.

Understanding territoriality is critical for conservation planning. Territory size determines the minimum area required to support a viable population and directly informs reserve design. For species reintroductions, knowledge of how territorial structures form and stabilize is essential for predicting whether released individuals will successfully establish themselves in a new habitat. Territorial behavior can also impede range expansion, as established territory holders may resist the settlement of incoming individuals, potentially slowing the colonization of newly available habitat.