anting behavior. The rubbing of ant bodies against the feathers or sitting on an anthill allowing ants to crawl through the feathers. Ant bodies are covered with a bitter chemical called formic acid, which may afford some protection from mites and lice. People have reported birds anting with items such as mothballs, cigarette butts, and onions.
aspect ratio. How long a wing is compared to how wide it is. This determines how a bird soars. High aspect ratios (long, narrow wings) allow flight at high speeds at low altitudes, while being extremely maneuverable. Low aspect ratios (broader wings) are adapted to slow speed, high altitude, effortless flight. Bird wings with aspect ratios at either extreme make taking off from the ground without a stiff headwind difficult.
austral migrants. Birds that breed in the Southern Hemisphere and migrate north for their winter.
brood parasites. Birds that do not build a nest or care for their young directly, instead searching out host nests in which to lay their eggs.
brood patch. A bare spot on the belly or chest where a bird’s body heat warms the eggs.
cloaca. The opening chamber to the intestines, ureters, and sex organs.
contour feathers. The outer feathers that keep moisture and wind out and streamline a bird.
countersinging. When neighboring birds sing in response to each other.
distraction display. Feigning an injury with loud calls and drooping wings to draw predators away from the nest.
diurnal migrants. Birds that migrate during the day.
down feathers. The inner feathers that trap air, providing insulation to hold body heat inside.
generalists. Bird species that can obtain everything they need from a variety of habitats.
gizzard. A muscular chamber of the stomach that mashes the food.
glottis. A fairly large opening on the bottom of the bird’s mouth where the trachea begins.
guano. The fecal and urinary waste of birds, especially seabirds, which contains a lot of uric acid and is collected for nitrogen- and phosphorus-rich fertilizers.
innate behavior (also instinctive behavior). A behavior that birds do in a particular situation without learning or trying that behavior beforehand.
indeterminate layer. A bird that will continue laying more eggs for a long time if its eggs are removed one by one.
insectivores. Birds that feed primarily on insects.
isotherm. The “line” visible on a weather map where temperatures average a particular temperature.
kettle. A swirling mass of hawks numbering anywhere from several to many thousands.
lacrimal gland. A tear gland at the base of the nictitating membrane that maximizes lubrication during blinking.
lek. An area where males gather to display and attract mates.
migrational orientation. Taking a direction and keeping it during a leg of migration.
mimids. Birds in the mockingbird family, including thrashers and catbirds.
neotropical migrants. Birds that spend winter in the Caribbean or Central or South America and breed in temperate North America.
nictitating membrane. A semitransparent inner eyelid that helps protect bird eyes and keep them moist.
nocturnal migrants. Birds that migrate at night.
owl pellets. The bones, fur, teeth, and other indigestible matter that an owl regurgitates in a dense, compact mass.
perching reflex. A mechanism whereby the stretched tendons of the lower leg automatically flex the foot around the branch and lock it in place while a bird is perching.
proventriculus. A glandular chamber of the stomach where powerful acids start dissolving the food.
rictal bristles. Specialized feathers found near the beaks of some insect-eating birds that provide tactile sensitivity and may sometimes help funnel insects into the bird’s mouth.
shadowboxing. A nontechnical term for when a bird fights with its own reflection in a window or mirror.
socially monogamous. Birds that defend a territory and raise young as a pair, but may sometimes mate with other individuals.
specialists. Bird species that have restricted habitat, nesting, or food needs.
syrinx (also song box). The structure used by birds to produce sound, located where the trachea branches into the bronchial tubes. The separate branches and sets of muscles allow many species to produce harmony with their own voice.
tubenose. A name for some ocean birds, such as albatrosses, that have huge glands that excrete salt at the end of “tubes” on their upper bills.
unihemispheric slow-wave sleep. A state in which one side of the brain may be asleep while the other half is awake.
uropygial gland (also preen gland). A gland found at the base of the tail that produces drops of oil used by birds to keep their feathers in good condition.
vanes. The webbed sides of the feather.
Wulst. The area of the brain that processes information from both eyes to provide stereoscopic vision.
Zugunruhe. Migratory restlessness in response to changing day length and/or the changing angle of the sun in the sky. Virtually all migratory species experience this urge, including individuals that have been hatched and reared in captivity.