A method used by animals to conceal themselves from an enemy by appearing to be a section of the natural background. Animal camouflage is a strategy that animal organisms use to avoid or deflect the attacks of predators by misleading the latter's visual senses. With the use of camouflage, animals can blend in with their surroundings (Fig. 1). In general, visual camouflage is recognized as one of the commonest and most powerful forces in natural selection and is found in nearly every ecosystem on Earth; yet, curiously, it is one of the least-studied phenomena in biology. Camouflage patterns (resulting from pigmentation, which is the property of biological materials to impart coloration) have evolved in animals of every size and shape, including both invertebrates and vertebrates, and occur in aquatic and terrestrial habitats. Camouflage is even employed at night, which is a seemingly odd notion until it is realized that many nocturnal predators have specialized visual systems for seeing well under lighting conditions that humans cannot perceive. See also: Behavioral ecology; Physiological ecology (animal); Pigmentation; Predator-prey interactions; Protective coloration

A discipline within the field of animal behavior that focuses on the reception and use of signals. Animal communication could well include all of animal behavior because a liberal definition of the term signal could encompass all stimuli perceived by an animal. However, most research in animal communication deals only with those cases in which one member of a species generates a signal, defined as a structured stimulus, that subsequently influences the behavior of another member of the same species in a predictable way (intraspecific communication) [Fig. 1]. In this context, communication occurs in virtually all animal species, if only as a means by which a member of one sex finds its partner. In general, the field of animal communication includes an analysis of the physical characteristics of those signals believed to be responsible in any given case of information transfer. See also: Ethology; Instinctive behavior; Neuroethology; Physiological ecology (animal); Primate communication

The cultivation of freshwater and marine species for human purposes. Aquaculture, or aquatic farming, is concerned with the raising of animals and the harvesting of plants in freshwater and marine environments (Fig. 1). In other words, it is the aquatic equivalent of land-based agriculture. When marine species are involved, aquaculture is often referred to as mariculture. The concept of aquaculture is not new, having begun in China about 4000 years ago, and the practice of fish culture there has been handed down through the generations. Today, aquaculture is a modern, multidisciplinary technology. Overall, aquaculture accounts for approximately half of the world's production of fish and shellfish, according to the Food and Agriculture Organization of the United Nations. See also: Agricultural science (animal); Agricultural science (plant); Agriculture; Fisheries ecology; Marine conservation; Marine ecology; Marine fisheries

A parasitic disease caused by a roundworm typically found in raccoons that is transmissible to humans, other mammals, and birds. Baylisascaris procyonis is a parasitic roundworm of raccoons (Procyon lotor) and belongs to the order Ascaridida in the phylum Nematoda (Nemata). This large parasite, which is commonly termed raccoon roundworm, is responsible for the disease baylisascariasis in animals and humans. The disease is manifested by severe or fatal visceral larval migrans, ocular larval migrans, and neurological disease (neurological larval migrans) in both animals and humans. Larval migrans is defined as the prolonged migration and persistence of helminth larvae in the organs and tissues of animals or humans. This infection is considered by the Centers for Disease Control and Prevention as an emerging zoonosis (a disease of animals that is transmissible to humans) in the United States. It was first reported in the United States in 1931 from a raccoon in the New York Zoological Park (now known as the Bronx Zoo). The infection appears to be common in raccoons across the United States, including California, the Midwest, the Northeast region, the Middle Atlantic region, and the mountainous areas of the southeastern states. The first human case was reported in 1984 in a 10-month-old child in Pennsylvania. At least 16 severe cases (including 6 fatalities) have been reported and well documented in humans. The prevalence of subclinical cases is unknown. See also: Ascaridida; Infection; Nemata (Nematoda); Parasitology; Raccoon; Zoonoses

The branch of ecology that focuses on the evolutionary causes of variation in behavior among populations and species. The scientific study of behavioral ecology investigates how changes of behavior are influenced by ecological factors (Fig. 1). Thus, behavioral ecology is concerned with the adaptiveness of behavior, as well as the ultimate questions of why animals behave as they do, rather than the proximate questions of how they behave. The principles of natural selection are applied to behavior with the underlying assumption that, within the constraints of their evolutionary histories, animals behave optimally by maximizing their genetic contribution to future generations. Several aspects of both individual and social behavior have been analyzed from this perspective. See also: Animal evolution; Behavior genetics; Ecology; Ethology; Instinctive behavior; Social mammals; Sociobiology

The study of behavior change in response to drugs, chemicals, or other environmental conditions or agents. Behavioral toxicology investigates the effect of toxic exposure on organismal behavior. The toxic exposure can involve various chemicals, drugs, or other environmental conditions or agents, which are collectively referred to as toxicants or toxins. Importantly, changes in behavior, as well as changes in sensation, mood, intellectual function, and motor coordination, are used by behavioral toxicologists to identify risks associated with exposure to potential toxicants and to determine mechanisms by which toxicants can affect the central nervous system (see figure). The information gained through behavioral toxicology can be used by scientists and government agencies to set limits in permissible levels of exposure to an environmental toxicant. Techniques employed in behavioral toxicology include epidemiologic surveys, field-based research, and laboratory-based experiments using human or nonhuman subjects. See also: Central nervous system; Environmental toxicology; Forensic toxicology; Nervous system disorders; Toxicology; Toxin

The biological diversity of different plant and animal species living on the island of Borneo. Borneo is the third largest island in the world. Located in Southeast Asia and straddling the Equator, it is divided among three countries: Indonesia, Malaysia, and Brunei. The largest part of Borneo, comprising the southern and eastern parts of the island, is Indonesian territory and often referred to as Kalimantan, whereas the northern part belongs to Malaysia (the states of Sarawak and Sabah) and Brunei (Fig. 1). Ecologically, Borneo has a profusion of tropical rainforests and is one of the most important centers of biodiversity in the world, with numerous plant and animal species having evolved on and inhabiting the island. As such, the natural richness and biological diversity of Borneo have attracted scientists, and dozens of new species of plants and animals are being discovered annually. However, it takes much effort to uncover the natural secrets of the island because the interior of the island is a remote area that is difficult to reach. Most of it is very mountainous, and few inland roads exist. See also: Animal evolution; Biodiversity; East Indies; Ecological communities; Island biogeography; Oceanic islands as evolutionary laboratories; Plant evolution; Plant geography; Rainforest; Speciation; Zoogeography

Any terrestrial or aquatic animal that is capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows for protective purposes, as well as for nesting, hibernation, warmth, and food storage. Burrows vary from temporary structures of simple design (for example, the nesting burrows of some birds) to more permanent underground networks that may be inhabited for several generations (for example, rabbit warrens, badger sets, fox earths, and prairie dog burrows; Fig. 1). They vary in structure from blind burrows with a single opening to extensive systems with several openings. Some animals (for example, various species of moles) live permanently underground, and their burrows have no obvious large openings to the surface. Burrows may be shared by a number of species, and abandoned burrows may be used by other species. Animals with limbs usually excavate their burrows by using their legs, but many burrowing animals are limbless and the mechanism of progression is not always obvious. See also: Adaptation (biology); Ecology; Hibernation and estivation

A member of the mammalian family Camelidae in the order Artiodactyla. Camels are even-toed, hoofed mammals (ungulates). There are three extant camel species: the Bactrian camel (Camelus bactrianus; Fig. 1), the wild Bactrian camel (C. ferus), and the Arabian or dromedary camel (C. dromedarius). Bactrian and Arabian camels species are domesticated. Herds of wild Bactrian camels are still in existence in the Gobi desert in northwestern China and southwestern Mongolia, but these animals are critically endangered. The three species are able to interbreed. See also: Artiodactyla; Domestication; Endangered species; Mammalia

A large homopteran insect of the superfamily Cicadoidea generally having long transparent wings and with the male typically producing a loud, droning noise. Cicadas are a large and diverse group of insects belonging to the superfamily Cicadoidea (suborder Auchenorrhyncha) in the order Hemiptera (class Insecta, phylum Arthropoda). There are two families: Cicadidae (with more than 1300 species globally distributed) and Tettigarctidae (with 2 species found in Australia). Most cicadas have a distinctive body form, with two pairs of wings, widely offset compound eyes on each side of the head, and three simple eyes (ocelli) on top of the head (Fig. 1). They are generally large insects, ranging from 12 to 50 mm (0.5 to 2 in.). At rest, the wings are held along the sides of the body, and they generally extend beyond the abdomen without overlapping. Cicadas may be brightly or cryptically colored, and they often have transparent wings. In many species, males produce distinctive sounds with specialized tymbal organs located on the abdomen. All cicadas are plant feeders with piercing mouthparts. Cicadas show especially high diversity in tropical regions. See also: Hemiptera; Insecta; Photoreception; Zoogeography