Chapter 29: Birds
Birds are used as animal models in studies of neurobiology, behavior, endocrinology, nutrition, microbiology, and embryology. Most birds used in research are domesticated fowl specifically bred for research and for which husbandry standards and diets are available.
While birds bred for research are not regulated under the Animal Welfare Act, they are covered species under PHS Policy. Guidelines for the care of birds are found in both the Guide and the Ag Guide.
Birds belong to the taxonomic class Aves, which is a large and diverse group.
Most birds used in research belong to three orders within this class:
Galliformes includes chickens, turkeys, quail, (which are commonly known as poultry).
Columbiformes includes pigeons and doves.
Passeriformes includes crows, sparrows, and finches, and are commonly known as passerines.
White Carneau pigeons, zebrafinches, and domestic chickens are valuable animal models in learning, memory, language development, atherosclerosis, and infectious disease research.
Bird anatomy, including wings and hollow bones, facilitates flight but makes them fragile. Male galliformes, like roosters, have spurs used for fighting and may require removal or trimming for safety.
Birds have unique digestive features, including a crop for food storage and a gizzard for grinding food. They excrete waste through a cloaca, which also serves reproductive and urinary functions.
Male birds have two testes and no accessory sex glands, while most female birds have only one functional ovary and oviduct. Eggs are fertilized in the oviduct, develop a shell, and are laid through the cloaca.
The male bird has two testes in the abdominal cavity, near the kidneys; there are no accessory sex glands. In most female birds, only the left ovary and oviduct are functional; the right one exists only in rudimentary form. For most birds, copulation involves a “cloacal kiss” where the male perches on the female’s back and twists his tail beneath her to deposit sperm in her cloaca. The egg travels from the ovary through a tube called the oviduct, where it is fertilized, surrounded by a layer of albumen (the egg white), and finally is enveloped in a hard shell before passing to the outside, blunt end first, through the cloaca (Figure 29.4).
In some research programs, eggs are collected and held before incubation for investigative assay or for later artificial batch incubation. Eggs that have been naturally incubated by the females for a few days may have higher incubator hatchability. Eggs collected for these purposes should be freshly laid and not washed. Cracked eggs should be culled. If embryo development has already begun, interrupting incubation may kill or damage the embryo. These eggs should not be held, but should continue to be incubated. In some species, eggs to be incubated later can be held for 7 to 14 days at 11 °C to 17 °C and 70% relative humidity.
Chickens can be restrained by holding their wings and legs, but should be carried upright to avoid stress. Tonic immobility, a fear response, can be induced by holding them upside down, but should be avoided.
Turkeys are easy to handle, even though they are stronger than chickens. Small turkeys can be handled like chickens, while larger ones may require a cloth to cover the head and caution due to their powerful wings.
Nets can be used to capture Columbiformes and passerines, but manual methods are preferred for smaller birds. When handling, avoid encircling the thorax completely to prevent respiratory issues.
Leg bands, color-coded or alphanumeric, are the usual method of identifying individual birds. Other identification methods include wing tags for larger birds.
The Guide recommends an ambient air temperature of 16 °C to 27 °C (61 °F to 81 °F) for poultry, with a relative humidity of 30% to 70%. Temperature, humidity, ventilation, and air filtration must be carefully controlled in indoor enclosures. Because birds are susceptible to temperature stress, ventilation is very important. As the environmental temperature rises, ventilation should be increased.2
Very young birds require an external heat source to prevent chilling and hypothermia. Special heated cages called “brooders” are used to house young birds until they grow their feathers.
The nutritional requirements of chickens are well known, and commercial feed preparations are usually adequate.4 The nutritional requirements of non-domestic avian species are largely unknown. Dietary requirements of seed-eating pigeons and doves are not as well understood as those of poultry. Several types of commercial pigeon diets are available. Specific seed mixtures can also be fed.
The order Passeriformes contains more than 4,800 species. Accordingly, there is a wide variation in nutritional requirements within this group. Only seed-eating passerines are discussed in this text, since they are the most common type used in biomedical research. Examples of seed eaters include sparrows, finches, and canaries. Usually a mixture of small seeds is fed; the most important seeds in the mix are canary grass seed and millet. Other components of the diet vary according to the species, and may include vegetables, fruits, grasses, cooked egg yolk, vitamin supplements, breads, and live insects. These items are freshly prepared and fed separately.5
Grit is essential for birds to grind seeds in their gizzards, aiding digestion. Various types of grit are available, and cuttlebone is recommended for passerines to maintain their beaks and provide calcium.
To use nondomestic (wild) birds in research, thorough knowledge of the animals’ natural habitat, behavior, and diet is essential. The procurement, transport, possession, and treatment of wild birds and their eggs are governed by state and federal regulations. Investigators and other involved parties should contact the local state conservation agency (Natural Resources, Fish and Game, Parks and Wildlife) and the US Fish and Wildlife Service for the latest information on a species in question.
Wild birds may have difficulty adapting to laboratory housing. Close observation during captivity is important. The behavioral characteristics and natural habitat of the species should be considered. Specific habitat features should be incorporated into the housing accommodations as part of the enrichment program, such as hiding places, water baths, or substrates such as sand.
A quiet environment away from noisy laboratory species, such as swine and dogs, is essential for wild birds. Bird cages should be equipped with numerous perches placed at heights appropriate for the species, in locations that prevent the birds from soiling their feed and water. Birds should be shielded from visual disturbances, such as the movement of personnel or equipment, during the acclimation period. A bird cage can be shielded by partially covering it with a cloth.
Placing feed and water in several locations of varying height in the cage helps the birds locate these items. Observing the birds for several days can help determine the birds’ preferred locations for feed and water. Multiple feed and water sources also reduce the possibility of dominant or aggressive birds preventing others from eating or drinking. For some species, feed scattered on the floor may encourage eating until the birds lose their fear of the feed container and learn to accept feed from a dish.
A wide range of bird species are worked with in biomedical research. As such, environmental enrichment can range from simply playing background music or hanging toys in the cage, to promoting normal behaviors and social groupings. Birds respond well to visual cues and stimulation, and promoting behaviors such as foraging and nesting has been shown to be particularly beneficial for their well-being. Environments that limit the expression of these behaviors may be a source of frustration and result in feather pecking and other negative stereotypic behaviors, including cannibalism. The best enrichment for galliformes is social housing followed by providing perches and a substrate material for foraging. Enrichment measures should be introduced gradually to let the birds get used to them.
Nonspecific signs of pain or distress or illness in birds include crouched posture, a drooped head and neck, dull eyes, ruffled feathers, nonresponsive attitude, and isolation from other birds in the cage. Birds that are ill may also be easier to capture and restrain.
Acceptable euthanasia techniques include overdosing with barbiturate administered by intravenous injection, inhalant anesthesia gases, or carbon dioxide. Other techniques, such as cervical dislocation, decapitation, maceration, or use of other gases, require special training and are dependent on the size of the animal. These methods may only be used under specific circumstances, and require IACUC approval. Thoracic compression has historically been commonly used for field studies, but is listed as unacceptable in the current AVMA Guidelines.1