Smelling in Stereo

This chapter discusses the sense of smell of animals. One way of acquiring information from chemicals in the world is through smell. Just as with the other senses, smell is used for many things, from finding food, judging relatedness and kin, locating and assessing potential mates, marking and defending territories, and much more. The chapter focuses first on ants, which are quite representative of how olfaction broadly works in nature. Located on the antennae of many insects are the main sensory receptors for encoding aspects of the world, from temperature and humidity through to pressure. In insect olfaction, the organs in which the receptors are housed are the olfactory sensilla. Meanwhile, the sense of smell of dogs has contributed to their long working relationship with humans, from help in hunting to search and rescue. After being domesticated for so long, dogs are also extremely good at reading humans, and this has clearly been a valuable trait for breeders in producing a variety of working and companion dogs. Finally, the chapter looks at the eastern American mole, which is one of the several mammals that has been shown to smell in stereo. The findings in the stereo mole essentially parallel some of the features of sound detection, rather like the way in which owls zero in on hidden prey based on the noises they make.

For My Eyes Only

This chapter explores how vision is used by animals and the diversity in ways of seeing. It first details how colour vision works, focusing on the example of honeybees, which, like humans, are trichromatic and have good colour vision. Bees have a dedicated ultraviolet (UV) receptor, and then one for seeing shortwave (blue) and mediumwave (green) light. Other animals deviate more substantially, in that they have either more or fewer receptors used in colour vision, and hence different ‘dimensions’ of colour perception. The chapter then considers how jumping spiders use UV vision in identifying known or suitable prey species, as well as in mating. It also looks at polarisation vision in mantis shrimp. Mantis shrimp are bizarre in the number of receptors they have, each sensitive to different parts of the light spectrum. Finally, the chapter assesses how toads recognize prey from non-prey. The toad’s visual system acts as a ‘feature detector’ based on several stages of visual processing, producing a quick and appropriate response to a set of criteria that reliably encode objects of particular importance—in this case, food.

Singing Rats and Sonar Bats

This chapter examines how animals have evolved a wide range of hearing organs to detect features of sound, some responding more to changes in intensity, others more to changes in pressure. Ears have evolved numerous times independently and they can occur in a range of structures and body locations. Hearing has numerous functions. For many animals, it is vital for detecting threats, such as an approaching predator. Hearing is also critical to a variety of other activities, from communicating territory ownership and trying to attract a mate, to detecting prey items in the undergrowth, and even sometimes in navigation. Of all animals, the group that must surely have the most remarkable and sophisticated hearing is the bats. Many bat species can echolocate using sounds that they produce themselves. The chapter also looks at the auditory system of owls and how rodents produce ultrasonic calls, called ultrasonic vocalizations (USVs).

Sensing in the Anthropocene

This chapter examines how the growing understanding of the variety of sensory systems used by nature has inspired new technologies to benefit human lives and society. A growing area is biomimicry, which involves inventions inspired by nature, and this has included trying to copy the sensory systems of animals. Humans also use animals directly in many ways; tens of billions of birds are kept for food production, not to mention other animal groups. There is much potential for food industries and places such as zoos to adopt conditions that are tailored to the sensory worlds and wellbeing of the animals they keep. The chapter then addresses how humans are dramatically altering the sensory worlds of animals. It considers the impacts of chemical pollution, sound or noise pollution, light pollution, electromagnetic noise, and climate change on animal senses. Finally, the chapter looks at how knowledge of animal senses has been put to good use in seeking to solve one of the problems of humanity’s own creation, namely overfishing. The use of LED lights in fisheries as a way of preventing bycatch, especially of highly visual animals such as turtles, is very promising, and target species appear to be relatively unaffected.

Electric Attraction

This chapter assesses the ability of animals to detect and interpret electric information. While sharks often use chemical information to track down prey from a long distance, many species enlist their electric sense to detect electric cues and determine the prey’s precise location and direct their attacks. Although it is normally used for prey detection, the electric sense can sometimes be used in defence too. The chapter then explores the diversity of ways electricity is produced and used by weakly electric fish. Meanwhile, the platypus can use their electric sense both to avoid objects in the water and to locate small prey items. The echidna also has receptors on the tip of its snout that respond to electric information, but its electric sense seems quite limited. Finally, the chapter considers how bees are able to detect electric fields associated with flowers.

Homing Turtles and Animal Magnetism

This chapter studies the magnetic sense of animals. A magnetic sense is widespread in nature and allows a variety of animals to detect the Earth’s geomagnetic field, and to use this for orientation and navigation over short and longer distances. The chapter looks at how animals use magnetic cues and magnetic maps, which is illustrated by the much-studied sea turtles. Turtles inherit a magnetic map that allows them to calculate their position in the ocean and adjust their orientation appropriately so they can travel towards a specific goal. However, it is not only turtles that achieve remarkable feats of navigation. A number of fish species also travel great distances during different phases of their lives, often returning to natal spawning grounds to breed later on. Meanwhile, over twenty bird species have been clearly demonstrated to use magnetic information as a compass and to respond to different components of the magnetic field. The key evidence for how the avian magnetic sense works is based on a magnetite process.

A Plethora of Senses

This chapter discusses the variety of animal senses, how they work, what they are used for, and why such a staggering array of senses exists in nature. The senses found across animal species, and even among individuals of the same species, vary according to many factors. Animal senses are carefully refined through evolution and development for the things that matter most to them. To accomplish the numerous tasks every individual must perform, the senses are tuned to work best in the habitats where the creature lives and to acquire the best available sources of information. Sometimes, one or more of the senses are exquisitely tuned to a few crucial tasks an animal must perform in order to survive and reproduce successfully. Investment in different senses can also be flexible depending on the conditions under which an animal grows up. Through adaptation over many generations, species like blind cave fish can decrease investment in one sense in favour of another, but individual animals can also do this during their lives.

Stars of the Tactile World

This chapter addresses the supreme level of refinement found in many animals for analysing tactile and pressure information. It begins by looking at the sensory organ of the star-nosed mole. The mole’s star-shaped organ is used purely for collecting tactile information. The chapter then considers the Eimer’s organs which cover every appendage that comprises the nose, some of which are used for initial prey detection, while others are for identification. Owing to the number of Eimer’s organs, their tiny size, and the way that the sensory cells respond to patterns of stimulation across parts of each individual Eimer’s organ, the mole obtains exquisite detail on texture, almost to a microscopic level. The chapter also discusses the highly refined tactile sense of spiders, looking at how they rely on vibrations transmitted through the ground, the silk web strands, or the surface waves and air for prey detection and capture. Spiders are equipped with a variety of sensors to detect mechanical information, including fine hairs sensitive to wind movement and touch, and special organs called slit sensilla around the joints of legs that measure physical forces acting on the exoskeleton. Finally, the chapter studies the nature and function of integumentary sense organs or ISOs in both crocodiles and alligators. The heavily built bodies of crocodiles and alligators belie a high sensitivity, being able to detect the slightest changes in touch and pressure.