cats for specific physical traits rather than behavior or function (Montague et al. 2014). The past 150 years has seen the recognition of approximately 50 different cat breeds (Cat Fanciers Association 2020), although purebred cats make up only 6–8% of the total US cat population today (Bradshaw et al. 2012).
2.3 Sensory Perception
The sensory systems of the domestic cat, which are almost identical to other Felis wildcats, have evolved to allow these species to become efficient hunters under a variety of environmental conditions. Perception also dictates the manner by which cats communicate with one another and with humans (Brown and Bradshaw 2013).
2.3.1 Vision
Small rodents are typically active at dawn and dusk, and cats have evolved features to enhance low‐light vision for crepuscular hunting. Cats have large eyes, and their pupils greatly expand in dark conditions, allowing increased light transmission to the retina. The pupil can narrow to a very thin slit to protect the retina in bright lighting. The tapetum is a reflective layer of tissue in the choroid of the eye. In addition to creating the “eye shine” observed when passing a light across the eyes of a cat (and many other species) at night, this structure also allows any light entering the eye to be reflected and amplified (Houpt 2018). The cat’s retina contains about three times more rods than cones. Rods are photoreceptor cells responsible for night vision, but the sacrifice in cone density results in lower visual acuity and color perception. Cats probably have a dichromatic spectrum of mainly blues and greens (Bradshaw et al. 2012). Color is unlikely to be an important factor in a cat’s sensory world. Cats have binocular vision but may not be able to focus well on an object within a foot from the eyes. Caged cats are nearsighted compared to outdoor cats (Belkin et al. 1977). Excellent motion detection due to specialized neurocircuitry in the visual cortex is yet another sensory capability that greatly enhances predatory success.
2.3.2 Hearing
Cats are able to detect sounds between 45 and 64,000 Hz, including 10.5 octaves, which is one of the broadest hearing ranges of any mammalian species (Fay and Popper 1994). The high‐frequency, even ultrasonic sound perception is likely helpful for the detection of prey and possibly kitten communication, but the evolutionary function for detecting very low‐frequency sounds remains a mystery (Bradshaw et al. 2012). The pinnae, or external parts of the ear, are highly moveable, amplify sounds, and allow the cat to more easily pinpoint the location of the source. Additionally, the pinnae position can be used to visually communicate emotional information to a conspecific (Leyhausen 1979; Overall 2013).
2.3.3 Olfaction
The importance of olfactory signals in hunting and conspecific communication has not been well studied. Cats seem to rely less on smell to locate prey compared to dogs (Montague et al. 2014); nevertheless, cats have a relatively robust sense of smell based on the numbers of olfactory receptors (Shreve and Udell 2017). Olfaction in cats, as in most non‐human animals, is composed of both the main and accessory systems. The main olfactory system is responsible for scent detection, whereas the distinct secondary system identifies socially relevant chemicals, such as pheromones. At the center of the accessory system is the vomeronasal organ, a cluster of specialized sensory cells that sit above the nasopalatine bone and connect to both oral and nasal passages, allowing evaluation of both airborne and fluid‐borne molecules (Brown and Bradshaw 2013). The information is relayed to the emotional centers of the brain, which can permit the animal to physiologically and behaviorally prepare for the appropriate action, usually without any conscious awareness (Mills 2005). A cat using the accessory olfactory system can be observed holding the mouth slightly agape, during which the flicking tongue draws salient molecules into the incisive duct, then up to the vomeronasal organ. The flehmen or “gaping” behavior is most commonly seen when a cat smells a strange cat’s urine (Hart and Leedy 1987; Houpt 2018).
2.3.4 Taste
Cats are obligate carnivores and must consume prey animals to obtain essential compounds (Montague et al. 2014). Cats have relatively few taste buds and no ability to taste sweet substances, perhaps because cats have little need to detect plant‐based sugars as an energy source. Recent research has shown that cats do have bitter taste receptors, which may provide a means of toxin detection and avoidance (Lei et al. 2015).
2.3.5 Touch and Balance
Balance is due to an integration of information from the visual, vestibular, central, and peripheral nervous systems. Cats are famous for the ability to right themselves during a fall by reflexively twisting the head and spine to land on their feet. This righting reflex relies primarily on the fluid in the bony labyrinth and semicircular canals of the vestibular system (Cremieux et al. 1984).
Whiskers, or vibrissae, are richly innervated specialized hairs with follicles originating from deep in the subcutaneous skin layer on the face, head, and carpi of a cat (Dyce et al. 2010). Mechanical stimulation of the whiskers transmits information to the sensory cortex of the brain and allows the cat to gain information about environmental conditions and objects within close range. Most notably, whiskers provide important information about the movement of prey, kittens, and other social partners immediately adjacent to the cat. Touch becomes the primary sense at close range due to poor visual acuity at this distance (Bradshaw et al. 2012). The cat’s canine teeth and claws also have pressure receptors to aid in preventing the escape of prey once captured (Byers and Dong 1989).
At rest cat facial whiskers are positioned slightly backward, but when moving or aroused, whiskers move forward and away from the head to prepare for gathering information (Beaver 2003). Therefore, whisker position can be a form of conspecific visual communication as well.
2.4 Communication
2.4.1 Vocalization
Conspecific vocal communication is only heard during agonistic, sexual, or mother‐kitten encounters (Kiley‐Worthington 1984). Cats vocalize much more frequently to humans, primarily through the open‐mouthed meow (or miaow) sound, which functions as attention seeking with a learned component. Close‐range affiliative communications include the purr and the trill. The purr is a care‐soliciting behavior heard from kittens when nursing, during friendly interactions, or when the cat is mildly anxious or ill (Crowell‐Davis et al. 2004; Overall 2013). The chirr or trill is a modified, mostly closed‐mouth meow sound used in greeting. The estrus call is also a closed‐mouth vocalization heard from females during courtship and can be similar in character to a type of agonistic male cat call (Overall 2013; Wolski 1982). However, aggressive intercat vocalizations are usually open‐mouthed and include the hiss, spit, growl, snarl, growl, yowl, and shriek (Crowell‐Davis et al. 2004).
2.4.2 Scent
Urination, defecation, and scratching are behaviors used to disseminate olfactory information (Brown and Bradshaw 2013). Urine, feces, and sebaceous glands, predominantly located on the head, perianal area, and between the digits of the paws, are rich in information about an individual and, therefore, effective forms of olfactory communication. Head rubbing of objects or social targets leaves olfactory signals from sebaceous glands located on the temporal region of the head, under the chin, and around the lips. This head bunting behavior is often accompanied by purring (Crowell‐Davis et al. 2004). Pheromones have been identified from the cheek sebaceous glands (Pageat and Gaultier 2003) and are thought to be a form of conspecific social signaling.
2.4.3 Visual Signals
Body
