A
adaptive radiation
Diversification of a single type of organism into multiple types each adapted to a specialized environmental niche.
![adaptive radiation](images_gloss/adaptive radiation d28-1-001.jpg )
adaptive radiation      Carduelis tristis
air sacs
A set of thin-walled chamber that allow air to flow in a continuous direction in the lungs. The air sacs are depicted in blue.
![air sacs](images_gloss/air sacs d28-1-062.jpg )
air sacs      0
airfoil
A wing or other structure designed (or evolved) to provide lift and control in flight.
![airfoil](images_gloss/airfoil d28-1-002.jpg )
airfoil      0
albino
An animal lacking in pigments resulting in white feathers and reddish soft parts.
![albino](images_gloss/American Robin l11-10-018.jpg )
American Robin      Turdus migratorius
allopreening
Mutual preening between two birds.
![allopreening](images_gloss/Burrowing Owl c22-8-033.jpg )
Burrowing Owl      Athene cunicularia
alternate plumage
Breeding plumage or nuptial plumage.
![alternate plumage](images_gloss/Magnolia Warbler b57-10-069.jpg )
Magnolia Warbler      Setophaga magnolia
altricial
Born helpless, often naked with eyes closed.
![altricial](images_gloss/Palm Warbler j07-1-222.jpg )
Palm Warbler      Setophaga palmarum
alula
Three to five feathers in wrist of the wing that are used in slow flight or landing, much as slots on an airplane.
![alula](images_gloss/Rock Pigeon c22-33-079.jpg )
Rock Pigeon      Columba livia
anisodactlyl feet
Most common pattern of bird toes, with the hallux pointing to the rear and three toes pointing forward.
![anisodactlyl feet](images_gloss/Peregrine Falcon c22-45-038.jpg )
Peregrine Falcon      Falco peregrinus
aposematic
A warning signal that advertises the unpalatablity of a bird or other animal.
![aposematic](images_gloss/Black-headed Pitohui p06-5-247.jpg )
Black-headed Pitohui      Pitohui dichrous
auricular
Area around the ear opening on the side of a bird’s head. Note blue auricular feathers above.
![auricular](images_gloss/Green Violetear m47-7-007.jpg )
Green Violetear      Colibri thalassinus
axillary
Area between the body and ventral surface of the wing. Note black axillary feathers in Black-bellied Plover
![axillary](images_gloss/Black-bellied Plover h28-1-003.jpg )
Black-bellied Plover      Pluvialis squatarola
B     
basic plumage
Non-breeding or winter plumage - typically duller colored
![basic plumage](images_gloss/Magnolia Warbler b40-7-020.jpg )
Magnolia Warbler      Setophaga magnolia
belly
The ventral part of the bird below the breast and above the legs. Above, it is the red area above the legs.
![belly](images_gloss/Red-bellied Grackle f26-10-029.jpg )
Red-bellied Grackle      Hypopyrrhus pyrohypogaster
bill
The beak
![bill](images_gloss/Golden-collared Toucanet b57-18-362.jpg )
Golden-collared Toucanet      Selenidera reinwardtii
bill-wiping
The behavior of birds wiping the bill clean of sticky food or other substances after feeding
![bill-wiping](images_gloss/American Robin s60-5-022.jpg )
American Robin      Turdus migratorius
binocular vision
Three-dimensional vision resulting from overlapping fields of vision due to placement of the eyes facing forward
![binocular vision](images_gloss/Luzon Scops-Owl w02-15-094.jpg )
Luzon Scops-Owl      Otus longicornis
booming sacs
Inflatable offshoots of the esophagus covered with bright-colored skin used in courtship display
![booming sacs](images_gloss/Greater Sage-Grouse s52-6-002.jpg )
Greater Sage-Grouse      Centrocercus urophasianus
bounding flight
Undulating flight pattern with short bursts of flapping followed by wings folded against the body
![bounding flight](images_gloss/bounding flight d28-1-003.jpg )
bounding flight      0
bower
A structure built by males of certain promiscuous species to attract females
![bower](images_gloss/Gardener Bowerbird s45-7-138.jpg )
Gardener Bowerbird      Amblyornis inornatus
breast
The chest - the area between the throat andbelly. The blue in the front of this kingfisher corresponds to the area of the breast.
![breast](images_gloss/Blue-breasted Kingfisher e09-4-018.jpg )
Blue-breasted Kingfisher      Halcyon malimbica
bristles
Stiff feathers without vanes or barbules
![bristles](images_gloss/Bearded Barbet m48-1-013.jpg )
Bearded Barbet      Lybius dubius
bronchi
The air passageway that transports air from the trachea to the lungs
![bronchi](images_gloss/bronchi d28-1-004.jpg )
bronchi      0
brood
The young birds derived from one clutch of eggs
![brood](images_gloss/Mute Swan m17-35-021.jpg )
Mute Swan      Cygnus olor
brood parasite
A bird that lays its egg in the nest of another bird. Cowbirds and Old World cuckoos are the most familiar examples.
![brood parasite](images_gloss/Bronzed Cowbird n06-1-356.jpg )
Bronzed Cowbird      Molothrus aeneus
brood patch
A highly vascularized, featherless area on the belly of incubating birds
![brood patch](images_gloss/Large-billed Blue-Flycatcher w02-46-015.jpg )
Large-billed Blue-Flycatcher      Cyornis caerulata
C     
camouflage
Use of features that blend in with the environment to hide
![camouflage](images_gloss/Little Bittern t11-3-067.jpg )
Little Bittern      Ixobrychus minutus
carotenoid
Organic pigments derived from plants and used by birds to color feathers and soft parts
![carotenoid](images_gloss/Holub's Golden Weaver c17-19-028.jpg )
Holub's Golden Weaver      Ploceus xanthops
casques
Hollow, bony extension of the skull in hornbills, such as in some hornbills and cassowaries.
![casques](images_gloss/Great Hornbill b61-2-022.jpg )
Great Hornbill      Buceros bicornis
cavity nest
A nest in a hole in a tree, bank, or the ground
![cavity nest](images_gloss/Hyacinth Macaw u02-25-011.jpg )
Hyacinth Macaw      Anodorhynchus hyacinthinus
central fovea
An area of densely packed cells near the center of the retina that perceives sharper images
![central fovea](images_gloss/central fovea d28-1-005.jpg )
central fovea     
cere
Leathery skin around the nostrils in birds such as hawks and pigeons
![cere](images_gloss/Plumbeous Forest-Falcon w02-39-022.jpg )
Plumbeous Forest-Falcon      Micrastur plumbeus
chin
A small area directly behind the mandible
![chin](images_gloss/White-chinned Petrel p19-3-040.jpg )
White-chinned Petrel      Procellaria aequinoctialis
choacal protuberance
Enlargement of the cloacal region in some birds during breeding season, caused by the swelling of tubules that store sperm
![choacal protuberance](images_gloss/cloacal protuberance d28-1-009.jpg )
cloacal protuberance     
choana
An opening in the roof of the mouth that leads to the two nasal cavities
![choana](images_gloss/choana d28-1-006.jpg )
choana     
clay lick
An area of clay visited by birds, which eat the clay for its mineral content
![clay lick](images_gloss/Dusky-headed Parakeet g28-17-047.jpg )
Dusky-headed Parakeet      Aratinga weddellii
cline
A gradual change in characters of members of the same species along a gradient of environmental or geographical transition
![cline](images_gloss/cline d28-1-007.jpg )
cline     
cloaca
Common opening for excretory, urinary, and reproductive systems
![cloaca](images_gloss/Gentoo Penguin f20-11-035.jpg )
Gentoo Penguin      Pygoscelis papua
cloacal bursa
An organ off of the cloaca, active in young birds, that produces B cells, specialized white blood cells
![cloacal bursa](images_gloss/cloacal bursa d28-1-008.jpg )
cloacal bursa     
clutch
The set of eggs laid by a single female during one bout of nesting. Here is a clutch size of four.
![clutch](images_gloss/American Robin h23-24-038.jpg )
American Robin      Turdus migratorius
coevolution
Reciprocal adaptations evolved by two or more organisms in response to changes in the other species
![coevolution](images_gloss/coevolution d28-1-010.jpg )
coevolution     
colony
A group of birds nesting together
![colony](images_gloss/Black-browed Albatross t08-12-010.jpg )
Black-browed Albatross      Thalassarche melanophris
comb
A fleshy growth on the top of the head, especially in chickens
![comb](images_gloss/Red Junglefowl c22-33-057.jpg )
Red Junglefowl      Gallus gallus
commensal
A relationship between to animals that helps one species while being neither a help or hindrance to the other
![commensal](images_gloss/Cattle Egret m55-3-024.jpg )
Cattle Egret      Bubulcus ibis
communal roost
A site used by large numbers of birds to sleep
![communal roost](images_gloss/Cattle Egret c26-21-016.jpg )
Cattle Egret      Bubulcus ibis
cones
Color sensitive cells in the retina
![cones](images_gloss/cone d28-1-011.jpg )
cone     
contour feathers
The typical feathers covering a bird with a long central shaft and a broad vane
![contour feathers](images_gloss/Wild Turkey m17-51-059.jpg )
Wild Turkey      Meleagris gallopavo
convergent evolution
A situation where two unrelated species evolve similar features because of similar environments. Example: Yellow-throated Longclaw from Africa and Eastern Meadowlark from the Americas.
![convergent evolution](images_gloss/Yellow-throated Longclaw v01-7-002.jpg )
Yellow-throated Longclaw      Macronyx croceus
cooperative foraging
A feeding strategy in which individuals in a group benefit by working together to catch prey
![cooperative foraging](images_gloss/American White Pelican m17-22-002.jpg )
American White Pelican      Pelecanus erythrorhynchos
coracoid
Bone connecting the sternum to the shoulder
![coracoid](images_gloss/coracoid d28-1-012.jpg )
coracoid     
courtship display
Ritualized posturing and movements used mostly by males, or both sexes together, to attract mates
![courtship display](images_gloss/Western Grebe f20-9-636.jpg )
Western Grebe      Aechmophorus occidentalis
courtship feeding
Transfer of food from the male to the female during courtship and early stages of nesting
![courtship feeding](images_gloss/Gull-billed Tern l28-1-012.jpg )
Gull-billed Tern      Gelochelidon nilotica
coverts
Feathers that overlap wing or tail feathers, covering the base of those feathers
![coverts](images_gloss/Yellow-billed Stork m17-70-756.jpg )
Yellow-billed Stork      Mycteria ibis
crèche
A group of bird chicks from different broods attended by a smaller number of adults, freeing other parents to forage
![crèche](images_gloss/Emperor Penguin t08-8-035.jpg )
Emperor Penguin      Aptenodytes forsteri
crepuscular
Active at dusk or dawn
![crepuscular](images_gloss/European Nightjar t08-13-660.jpg )
European Nightjar      Caprimulgus europaeus
crop
A sac off of the esophagus used to store food
![crop](images_gloss/Harris's Hawk f20-10-062.jpg )
Harris's Hawk      Parabuteo unicinctus
crop milk
Liquid protein from cells grown in a pigeon's crop. Also known as pigeon milk.
![crop milk](images_gloss/Mourning Dove t12-1-402.jpg )
Mourning Dove      Zenaida macroura
crown
The top of a birds head
![crown](images_gloss/Blue-crowned Manakin w02-11-244.jpg )
Blue-crowned Manakin      Lepidothrix coronata
cup nest
An open nest with a shape like a teacup minus the handle
![cup nest](images_gloss/Hooded Warbler a23-1-009.jpg )
Hooded Warbler      Setophaga citrina
D     
decurved
Curved in a downward fashion
![decurved](images_gloss/Long-billed Curlew m17-63-106.jpg )
Long-billed Curlew      Numenius americanus
disjunct range
An area of distribution for an organism that is separate from the main area of distribution
![disjunct range](images_gloss/disjunct range d28-1-013.jpg )
disjunct range     
distraction display
Actions taken by a parent bird, such as feigning a broken wing, or acting uncoordinated to distract a predator from the nest or chicks
![distraction display](images_gloss/Killdeer u02-3-004.jpg )
Killdeer      Charadrius vociferus
#N/Adown feathers
Fluffy, soft feathers of young birds or similar feathers beneath the contour feathers of some adult birds
![down feathers](images_gloss/Red-footed Booby a16-8-189.jpg )
Red-footed Booby      Sula sula
drag
The force that resists movement through the air
![drag](images_gloss/drag force d28-1-014.jpg )
drag force     
drumming
The beating of the wings by a grouse during courtship causing the air to make a thumping sound. Also the rapid hammering of a woodpecker to create a sound proclaiming its territory
![drumming](images_gloss/Ruffed Grouse n10-18-038.jpg )
Ruffed Grouse      Bonasa umbellus
dust-bathing
Crouching and fluttering in dust or dry dirt to spread fine particles into feathers to get rid of ectoparasites and maintain feathers
![dust-bathing](images_gloss/Northern Bobwhite m17-74-127.jpg )
Northern Bobwhite      Colinus virginianus
dynamic soaring
A mode of flight in which the bird gains energy by repeatedly crossing between air masses with different velocities. Albatrosses, for example, gain lift by repeatedly crossing from the calm of a wave trough to headwinds above the waves.
![dynamic soaring](images_gloss/dynamic soaring d28-1-015.jpg )
dynamic soaring     
E     
eclipse plumage
A female-like plumage acquired by male ducks and some other birds after breeding
![eclipse plumage](images_gloss/Mallard m17-35-025.jpg )
Mallard      Anas platyrhynchos
ectoparasite
A parasite that lives on the outside of an animal, such as a tick, mite, or leech
![ectoparasite](images_gloss/Red-legged Thrush w02-28-198.jpg )
Red-legged Thrush      Turdus plumbeus
egg
The reproductive product of a bird
![egg](images_gloss/Brown-headed Cowbird s39-2-127.jpg )
Brown-headed Cowbird      Molothrus ater
egg tooth
A small sharp knob near the tip of the beak that helps the chick break open the egg. It falls of or is resorbed within a few days of hatching.
![egg tooth](images_gloss/Laughing Gull w02-53-127.jpg )
Laughing Gull      Leucophaeus atricilla
embryo
The developing chick within an egg
![embryo](images_gloss/Atlantic Petrel a25-1-012.jpg )
Atlantic Petrel      Pterodroma incerta
epaulettes
Bright-colored patches of feathers at the base of a bird's wings
![epaulettes](images_gloss/Long-tailed Widowbird t11-3-633.jpg )
Long-tailed Widowbird      Euplectes progne
esophagus
The passageway from the mouth to the stomach
![esophagus](images_gloss/esophagus d28-1-016.jpg )
esophagus     
external ear
The open of the ear leading to the tympanum or ear drum. In most birds it is shallow and covered with specialized feathers.
![external ear](images_gloss/Double-wattled Cassowary s66-3-001.jpg )
Double-wattled Cassowary      Casuafalcorius casuarius
eye comb
A bright-colored skin over the eye in some birds such as grouse
![eye comb](images_gloss/Spruce Grouse b53-4-120.jpg )
Spruce Grouse      Falcipennis canadensis
eye ring
A circle of bare skin immediately around the eye
![eye ring](images_gloss/Dagua Thrush w02-39-291.jpg )
Dagua Thrush      Turdus daguae
eyeline
A line created by colored feathers that continues on both sides of the eye
![eyeline](images_gloss/Chipping Sparrow n10-15-011.jpg )
Chipping Sparrow      Spizella passerina
F     
feather tracts
Regions of skin where feathers attach, also known as pterylae. Here seen as dark bands on lighter skin.
![feather tracts](images_gloss/Painted Bunting r25-1-054.jpg )
Painted Bunting      Passerina ciris
fecal sac
A membrane covered packet containing the feces and uric acid that is collected from the chick's cloaca by the parent bird
![fecal sac](images_gloss/Red-eyed Vireo h23-24-046.jpg )
Red-eyed Vireo      Vireo olivaceus
femur
The proximal (upper) leg bone
![femur](images_gloss/femur d28-1-017.jpg )
femur     
fibula
The smaller of two bones on the shin or calf, familiar to many as the skinny bone in the drumstick
![fibula](images_gloss/fibula d28-1-018.jpg )
fibula     
filoplumes
Fine, vaneless, hairlike feathers that have sensory receptors adjacent to their follicles
![filoplumes](images_gloss/Yellow-bellied Bulbul w02-48-342.jpg )
Yellow-bellied Bulbul      Criniger phaeocephalus
flank
The upper sides of a bird
![flank](images_gloss/Hooded Merganser c22-35-109.jpg )
Hooded Merganser      Lophodytes cucullatus
fledgling
A chick that has recently flown from the nest for the first time
![fledgling](images_gloss/White-crowned Pigeon c34-2-023.jpg )
White-crowned Pigeon      Patagioenas leucocephala
flight feathers
The remiges and retrices--major tail and wing feathers
![flight feathers](images_gloss/Egyptian Vulture e05-4-167.jpg )
Egyptian Vulture      Neophron percnopterus
flight song
A courtship or territorial song sung in flight
![flight song](images_gloss/European Sedge-Warbler t08-16-066.jpg )
European Sedge-Warbler      Acrocephalus schoenobaenus
forehead
The part of the crown just above the beak
![forehead](images_gloss/Plushcap w02-38-246.jpg )
Plushcap      Catamblyrhynchus diadema
forked tail
A tail with a notch in the center
![forked tail](images_gloss/Fork-tailed Drongo t11-2-126.jpg )
Fork-tailed Drongo      Dicrurus adsimilis
frugivorous
Eating fruit as the major part of the diet
![frugivorous](images_gloss/Fawn-breasted Tanager b57-18-195.jpg )
Fawn-breasted Tanager      Pipraeidea melanonota
furcula
The fused clavicles of a bird - popularly known as the wishbone
![furcula](images_gloss/furcula d28-1-019.jpg )
furcula     
G     
gape flange
The soft tissue where the two halves of the jaw join--often conspicuous in nestlings and juvenile birds
![gape flange](images_gloss/Ocellated Antbird w02-41-319.jpg )
Ocellated Antbird      Phaenostictus mcleannani
gizzard
The muscular section of the avian stomach which grinds food
![gizzard](images_gloss/gizzard d28-1-020.jpg )
gizzard     
gleaning
Picking prey off of leaves and other surfaces
![gleaning](images_gloss/Swainson's Thrush c22-41-132.jpg )
Swainson's Thrush      Catharus ustulatus
glenoid fossa
The rounded depression in the scapula that articulates with the head of the humerus and allows the wing to rotate
![glenoid fossa](images_gloss/glenoid fossa d28-1-021.jpg )
glenoid fossa     
gliding
Flying without flapping while losing altitude slowly
![gliding](images_gloss/gliding d28-1-022.jpg )
gliding     
globular nest
A spherical nest, typically with the opening on the side
![globular nest](images_gloss/Grosbeak Weaver d07-11-023.jpg )
Grosbeak Weaver      Amblyospiza albifrons
graduated tail
A tail in which the retrices are progressively longer toward the center
![graduated tail](images_gloss/Rose-ringed Parakeet e05-14-258.jpg )
Rose-ringed Parakeet      Psittacula krameri
grazing
Feeding on grass and other herbaceous plants
![grazing](images_gloss/Barnacle Goose e05-14-030.jpg )
Barnacle Goose      Branta leucopsis
greater coverts
The row feathers that lies immediately above the flight feathers (On the shoveler, the white row of feathers above the secondaries and the corresponding row over the primaries)
![greater coverts](images_gloss/Northern Shoveler t08-14-089.jpg )
Northern Shoveler      Anas clypeata
guano
The accumulated droppings of colonial birds, especially seabirds. It is mined as fertilizer in some places. Guano covers much of this hill.
![guano](images_gloss/Peruvian Booby e05-4-069.jpg )
Peruvian Booby      Sula variegata
guild
A group of birds in one area that exploits resources in a similar fashion. Illus. army ant followers in Panama: A Northern Barred Woodcreeper, B Plain Brown Woodcreeper, C Rufous-vented Ground-Cuckoo, D Ocellated Antbird, E Gray-headed Tanager, F Spotted Antbird, G Bicolored Antbird
![guild](images_gloss/guild d28-1-023.jpg )
guild     
gular Sac
Expandable pouch of skin just below the chin which can be used for panting to cool the bird
![gular Sac](images_gloss/Double-crested Cormorant m17-34-065.jpg )
Double-crested Cormorant      Phalacrocorax auritus
H     
hallux
The first toe, usually pointing backwards
![hallux](images_gloss/Wild Turkey l07-43-163.jpg )
Wild Turkey      Meleagris gallopavo
hatch
To emerge from the egg
![hatch](images_gloss/Gentoo Penguin g22-1-017.jpg )
Gentoo Penguin      Pygoscelis papua
hatchling
A bird that has just emerged from the egg
![hatchling](images_gloss/Lesser Frigatebird b15-7-026.jpg )
Lesser Frigatebird      Fregata ariel
hawking
Feeding by flying out from a perch to snatch prey and returning to that perch
![hawking](images_gloss/hawking d28-1-024.jpg )
hawking     
herbivore
An animal that eats plant material exclusively or almost so
![herbivore](images_gloss/Hoatzin s45-14-010.jpg )
Hoatzin      Opisthocomus hoazin
heterodactyl foot
A bird foot in which digits three and four face forward, while the first and second digit face backward. Trogons have this pattern.
![heterodactyl foot](images_gloss/Masked Trogon u02-29-027.jpg )
Masked Trogon      Trogon personatus
hooklets
Tiny hooks on the barbules of feathers that keep the barbs and barbules from separating
![hooklets](images_gloss/Hooklets d28-1-025.jpg )
Hooklets     
hover
Flying in a stationary position
![hover](images_gloss/Osprey m17-72-166.jpg )
Osprey      Pandion haliaetus
humerus
The wing bone closest to the body
![humerus](images_gloss/humerus d28-1-026.jpg )
humerus     
hybrid
A cross between two different species
![hybrid](images_gloss/Hybrid Duck Mallard x Pintail n10-10-010.jpg )
Hybrid Duck Mallard x Pintail      A. platyrhynchos x A. acuta
I     
ilium
The largest and uppermost bone in the pelvic girdle. It is fused with the ischium and synsacrum.girdle.
![ilium](images_gloss/ileum d28-1-027.jpg )
ileum     
imprinting
Behaviors that are learned and fixed during a limited critical period in a bird's early life
![imprinting](images_gloss/Upland Goose d09-2-195.jpg )
Upland Goose      Chloephaga picta
incubation
Maintaining the eggs at a constant temperature ideal for development. Most birds incubate by sitting on the eggs but megapodes incubate in compost or warm sand.
![incubation](images_gloss/Least Tern f20-9-398.jpg )
Least Tern      Sternula antillarum
infundibulum
The funnel shaped anterior end of the oviduct that accepts the egg during ovulation
![infundibulum](images_gloss/infundibulum d28-1-028.jpg )
infundibulum     
iridescence
Glittering colors that change with the angle of view, caused by structural features of feathers that scatter light. A famiiar example is the feathers on a Rock Pigeon's neck.
![iridescence](images_gloss/Nicobar Pigeon t08-16-043.jpg )
Nicobar Pigeon      Caloenas nicobarica
iris
The colored circular diaphragm in the eye that controls the amount of light hitting the retina
![iris](images_gloss/Semiplumbeous Hawk w02-39-010.jpg )
Semiplumbeous Hawk      Leucopternis semiplumbeus
ischium
The large pelvic bone posterior to the leg joint and fused with the posterior portion of the synsacrum
![ischium](images_gloss/ischium d28-1-029.jpg )
ischium     
J     
juvenile
A young bird, usually in the first months after fledging, that has its first set of contour feathers
![juvenile](images_gloss/Herring Gull o05-18-009.jpg )
Herring Gull      Larus argentatus
K     
keel
A large, flat ridge of bone that extends perpendicularly from the main portion of the sternum The major flight muscles, the pectoralis and the suprcoracoideus, attach to the keel. Also known as carina.
![keel](images_gloss/keel d28-1-030.jpg )
keel     
keratin
A fibrous protein that is the chief component of feathers, scales and claws
![keratin](images_gloss/Common Poorwill b13-3-021.jpg )
Common Poorwill      Phalaenoptilus nuttallii
kettle
A group of rising birds soaring in a spiral motion in a thermal
![kettle](images_gloss/Turkey Vulture m57-6-020.jpg )
Turkey Vulture      Cathartes aura
kleptoparasite
An animal that habitually steals food from another animal
![kleptoparasite](images_gloss/Magnificent Frigatebird h02-8-163.jpg )
Magnificent Frigatebird      Fregata magnificens
L     
lacrimal gland
The structure at the ventral side of the eye that secretes tears
![lacrimal gland](images_gloss/lacrimal glands d28-1-031.jpg )
lacrimal glands     
laminar flow
Smooth flow of air over the surface of the wing
![laminar flow](images_gloss/laminar flow d28-1-032.jpg )
laminar flow     
lek
A communal display ground for promiscuous male birds
![lek](images_gloss/Greater Sage-Grouse b53-4-154.jpg )
Greater Sage-Grouse      Centrocercus urophasianus
lens
The hard, transparent area inside the eye that focuses light
![lens](images_gloss/lens d28-1-033.jpg )
lens     
lesser coverts
The rows of feathers on the wing immediately over the greater coverts
![lesser coverts](images_gloss/African Pygmy Kingfisher w02-22-023.jpg )
African Pygmy Kingfisher      Ispidina picta
lore
The area between the eye and the beak--chartreuse on this breeding Great Egret
![lore](images_gloss/Great Egret m17-67-331.jpg )
Great Egret      Ardea alba
M     
malar region
The lower part of the face extending behind the lower beak, seen here in black on this Northern Flicker
![malar region](images_gloss/Northern Flicker m17-53-070.jpg )
Northern Flicker      Colaptes auratus
mandible
The lower half of the beak
![mandible](images_gloss/Black Skimmer m17-73-039.jpg )
Black Skimmer      Rynchops niger
melanism
Darkening of pigmented feathers due to extra melanin (a class of pigments) , in this case making a normally white Cattle Egret, blackish
![melanism](images_gloss/Cattle Egret t11-3-050.jpg )
Cattle Egret      Bubulcus ibis
mesobronchus
The extension of the bronchus inside the lungs leading to the abdominal air sacs
![mesobronchus](images_gloss/mesobronchi d28-1-034.jpg )
mesobronchi     
metacarpals
The three bones that fuse to form the carpometacarpus distal to the humerus
![metacarpals](images_gloss/metacarpal d28-1-035.jpg )
metacarpal     
migration
Seasonal movement of birds from one area to another
![migration](images_gloss/American White Pelican s70-2-016.jpg )
American White Pelican      Pelecanus erythrorhynchos
mimicry
In birds, most often used for vocal mimicry, in which one species imitates the vocalizations of another. Mockingbirds are "open-ended" learners and can add new songs to their repetoire thoughout their life.
![mimicry](images_gloss/Northern Mockingbird w02-54-052.jpg )
Northern Mockingbird      Mimus polyglottos
molt
Periodic loss and regrowth of feathers. This Ring-billed Gull shows wing molt.
![molt](images_gloss/Ring-billed Gull m17-67-649.jpg )
Ring-billed Gull      Larus delawarensis
monocular vision
Sight in which each eye is used separately with little overlap in the field of view of each eye
![monocular vision](images_gloss/American Woodcock c27-6-038.jpg )
American Woodcock      Scolopax minor
monogamy
Maintaining a single mate, at least for the duration of nesting
![monogamy](images_gloss/Scarlet Macaw b57-1-242.jpg )
Scarlet Macaw      Ara macao
morph
Groups of birds that differ in body size, bill shape, color or other features from other groups of birds of the same species. The two color morphs of Reddish egrets shown here.
![morph](images_gloss/Reddish Egret c22-36-260.jpg )
Reddish Egret      Egretta rufescens
mound nest
A nest made from a heap of sand, sticks or other material with an egg chamber inside, particularly those of the moundbuilders
![mound nest](images_gloss/Mallee Fowl b33-1-060.jpg )
Mallee Fowl      Leipoa ocellata
mycoplasmal conjunctivitis
A disease, most commonly observed in House Finches, in which the eye is swollen, crusty and sometimes shut
![mycoplasmal conjunctivitis](images_gloss/House Finch n10-15-019.jpg )
House Finch      Haemorhous mexicanus
N     
nape
The region at the back of the neck
![nape](images_gloss/Yellow-naped Parrot s68-2-113.jpg )
Yellow-naped Parrot      Amazona auropalliata
nares
The external openings of the nose
![nares](images_gloss/Turkey Vulture l07-55-216.jpg )
Turkey Vulture      Cathartes aura
natal down
Loose, fluffy feathers of young birds prior to developing contour feathers
![natal down](images_gloss/Whiskered Tern t11-3-273.jpg )
Whiskered Tern      Chlidonias hybrida
nest
The structure in which a bird lays and incubates its eggs
![nest](images_gloss/Black-browed Albatross s66-1-042.jpg )
Black-browed Albatross      Thalassarche melanophris
nest appropriation
Using the nest of another bird, typically after the other bird has ceased to use it. This horned owl has appropriated a hawk nest.
![nest appropriation](images_gloss/Great Horned Owl v11-19-163.jpg )
Great Horned Owl      Bubo virginianus
nictitating membrane
A transparent membrane that slides sideways over the eye, moistening or protecting it
![nictitating membrane](images_gloss/Red-headed Vulture h02-26-006.jpg )
Red-headed Vulture      Sarcogyps calvus
nidifugous
Leaving the nest shortly after hatching
![nidifugous](images_gloss/Dunlin m17-67-248.jpg )
Dunlin      Calidris alpina
nocturnal
Active at night
![nocturnal](images_gloss/Eastern Screech-Owl n06-1-191.jpg )
Eastern Screech-Owl      Megascops asio
O     
oil gland
A sebaceous gland near the dorsal base of the tail that produces oil for preening, also known as uropygial gland or preen gland
![oil gland](images_gloss/Black-crowned Night-Heron w02-35-002.jpg )
Black-crowned Night-Heron      Nycticorax nycticorax
omnivore
An animal that eats both plant and animal material
![omnivore](images_gloss/Gila Woodpecker b13-48-016.jpg )
Gila Woodpecker      Melanerpes uropygialis
operculum
A structure that covers the nares in some birds
![operculum](images_gloss/Rock Pigeon s36-27-002.jpg )
Rock Pigeon      Columba livia
oral flanges
See gape flanges
![oral flanges](images_gloss/Canyon Wren n10-16-004.jpg )
Canyon Wren      Catherpes mexicanus
oviduct
The long, convoluted tube through which the egg passes from ovary to cloaca. Albumin, membranes and egg shell are added in the oviduct.
![oviduct](images_gloss/oviduct d28-1-037.jpg )
oviduct     
P     
pamprodactyl feet
Feet with toes all arranged in a forward orientation, as in some swifts
![pamprodactyl feet](images_gloss/Chimney Swift l07-50-048.jpg )
Chimney Swift      Chaetura pelagica
pecten
A comb-shaped structure of blood vessels inside the avian eye extending out from the optic nerve. It is thought to nourish the retina and control the ph of the vitreous humor.
![pecten](images_gloss/pecten d28-1-038.jpg )
pecten     
pectinate claw
A claw with a comb-like edge found in heron family and in nightjars and Barn Owls. It is presumably used for preening.
![pectinate claw](images_gloss/Tricolored Heron m17-67-817.jpg )
Tricolored Heron      Egretta tricolor
pectoral girdle
The bones connecting the wing with the main part of the skeleton. It consists of the furcula, scapulas , coracoids , and sternum.
![pectoral girdle](images_gloss/pectoral girdle d28-1-039.jpg )
pectoral girdle     
pectoralis
The large breast muscle that powers the downstroke of flight by depressing the wing at the shoulder
![pectoralis](images_gloss/pectoralis major d28-1-040.jpg )
pectoralis major     
pelagic species
A bird that spends its life on the open ocean. Pelagic birds typically only coming to land to breed.
![pelagic species](images_gloss/Pink-footed Shearwater b57-10-134.jpg )
Pink-footed Shearwater      Puffinus creatopus
pellet
The regurgitated bolus of indigestible prey parts expelled by owls, kingfishers and other birds
![pellet](images_gloss/Snowy Owl c22-43-005.jpg )
Snowy Owl      Bubo scandiacus
pelvic girdle
The fused ilium, ischium, , pubis, and fused sacral vertebrae. Together they form an anchor for the tail and leg muscles.
![pelvic girdle](images_gloss/pelvic girdle d28-1-041.jpg )
pelvic girdle     
pendulous cup nest
A sock-shaped nest suspended from twigs, especially by orioles, oropendolas, and caciques.
![pendulous cup nest](images_gloss/Crested Oropendola f20-12-088.jpg )
Crested Oropendola      Psarocolius decumanus
pensile cup nest
A cuplike nest suspending by the rim typical of vireos, some blackbirds, and kinglets.
![pensile cup nest](images_gloss/Warbling Vireo a23-2-021.jpg )
Warbling Vireo      Vireo gilvus
phalanges
The finger bones--reduced in birds.
![phalanges](images_gloss/phalanges d28-1-042.jpg )
phalanges     
pigments
Chemical compounds that absorb light of specific wavelengths giving feathers and soft parts their colors.
![pigments](images_gloss/Scarlet Macaw s66-1-410.jpg )
Scarlet Macaw      Ara macao
pin feathers
Growing feathers still covered by the feather sheath
![pin feathers](images_gloss/Little Blue Heron d03-6-012.jpg )
Little Blue Heron      Egretta caerulea
pipped
Describing an egg that has a small hole made by a chick about to hatch
![pipped](images_gloss/American White Pelican w30-1-050.jpg )
American White Pelican      Pelecanus erythrorhynchos
piracy
Stealing food from other birds, typically from other species
![piracy](images_gloss/Brown Noddy h02-8-035.jpg )
Brown Noddy      Anous stolidus
platform nest
Nests built of sticks piled on each other with a low depression for the eggs
![platform nest](images_gloss/Osprey t12-1-220.jpg )
Osprey      Pandion haliaetus
plumage
The set of feathers that cover a bird, or a seasonal or age-related pattern of the feathers
![plumage](images_gloss/Scarlet Tanager s52-11-401.jpg )
Scarlet Tanager      Piranga olivacea
plunge diving
Diving from the air into water after prey using momentum to overcome buoyancy. Typical of pelicans, boobies, gannets, and most terns.
![plunge diving](images_gloss/Blue-footed Booby m17-74-018.jpg )
Blue-footed Booby      Sula nebouxii
pneumatic bones
Hollow bones containing extensions of air sacs. Their light weight makes them an important adaptation for flight.
![pneumatic bones](images_gloss/pneumatic bones d28-1-043.jpg )
pneumatic bones     
polyandry
A form of polygamy in which a female has more than one male mate at a time
![polyandry](images_gloss/Spotted Sandpiper n09-2-122.jpg )
Spotted Sandpiper      Actitis macularia
polygamy
A breeding system in which a member of one sex takes multiple mates of the opposite sex
![polygamy](images_gloss/Marsh Wren b61-1-031.jpg )
Marsh Wren      Cistothorus palustris
polygyny
Mating system in which each male may mate with multiple females
![polygyny](images_gloss/Red-winged Blackbird g28-14-002.jpg )
Red-winged Blackbird      Agelaius phoeniceus
polymorphism
Two or more different forms (at the same life stage) in the same species, such as two distinct color variations or morphs
![polymorphism](images_gloss/Ruff v01-7-001.jpg )
Ruff      Philomachus pugnax
porphyrins
A group of pigments responsible for certain brown and green feather coloration and in one case magenta
![porphyrins](images_gloss/Schalow's Turaco h02-5-112.jpg )
Schalow's Turaco      Tauraco schalowi
precocial
Baby birds hatched with down and with eyes open, ready to leave the nest
![precocial](images_gloss/Canada Goose w30-1-022.jpg )
Canada Goose      Branta canadensis
precopulatory display
Ritualized postures and vocalizations uniquely performed prior to copulation
![precopulatory display](images_gloss/Yellow-headed Blackbird w30-1-006.jpg )
Yellow-headed Blackbird      Xanthocephalus xanthocephalus
preening
Cleaning and arranging the feathers typically with the beak
![preening](images_gloss/White Ibis f20-9-644.jpg )
White Ibis      Eudocimus albus
premaxilla
The main bone of the upper half of the beak
![premaxilla](images_gloss/premaxilla d28-1-044.jpg )
premaxilla     
primaries
Flight feathers attached to the outermost segment of the wing. In the Palm Nut Vulture they have white bases.
![primaries](images_gloss/Palm-nut Vulture m51-4-061.jpg )
Palm-nut Vulture      Gypohierax angolensis
promiscuous
Describing a species in which one sex breeds with multiple mates
![promiscuous](images_gloss/Greater Sage-Grouse s52-16-068.jpg )
Greater Sage-Grouse      Centrocercus urophasianus
proventriculus
The glandular chamber of the avian stomach between the esophagus and the gizzard
![proventriculus](images_gloss/proventriculus d28-1-045.jpg )
proventriculus     
pupil
The opening in the center of the eye, through which light passes
![pupil](images_gloss/Scale-feathered Cuckoo w02-15-353.jpg )
Scale-feathered Cuckoo      Lepidogrammus cumingi
pygostyle
The last bone at the posterior end of the vertebral column, which supports the tail feathers and related musculature. It is formed by several fused vertebrae.
![pygostyle](images_gloss/pygostyle d28-1-046.jpg )
pygostyle     
Q     
     
rachis
The outer portion of the shaft (central support) of the feather that supports the vanes
![rachis](images_gloss/Canada Goose w02-53-029.jpg )
Canada Goose      Branta canadensis
radius
The smaller of paired bones in the middle section of the wing
![radius](images_gloss/radius d28-1-047.jpg )
radius     
recurved
Curved upwards, as in the beak of an avocet
![recurved](images_gloss/American Avocet m55-3-006.jpg )
American Avocet      Recurvirostra americana
remiges
The flight feathers of the wing -- the primaries and secondaries combined
![remiges](images_gloss/Greater Scaup c22-39-150.jpg )
Greater Scaup      Aythya marila
retort nest
A globular nest with an entrance tunnel
![retort nest](images_gloss/Lesser Masked Weaver l07-44-061.jpg )
Lesser Masked Weaver      Ploceus intermedius
retrices
The major feathers of the tail
![retrices](images_gloss/Red-tailed Hawk s65-1-048.jpg )
Red-tailed Hawk      Buteo jamaicensis
rhamphotheca
A horny sheath of keratin that covers the beak
![rhamphotheca](images_gloss/rhampotheca d28-1-048.jpg )
rhampotheca     
rictal bristles
Stiff whisker-like feathers around the gape, most commonly found in aerial feeders, which presumably help to guide food into the mouth
![rictal bristles](images_gloss/Tawny-breasted Flycatcher w02-38-277.jpg )
Tawny-breasted Flycatcher      Myiobius villosus
rump
The region between the back and the tail on the dorsal side of the bird
![rump](images_gloss/Scarlet-rumped Cacique w02-41-234.jpg )
Scarlet-rumped Cacique      Cacicus uropygialis
S     
sacral vertebrae
Vertebrae just anterior to the caudal vertebrae, which are fused as part of the synsacrum
![sacral vertebrae](images_gloss/sacral vertebrae d28-1-049.jpg )
sacral vertebrae     
salt gland
An organ for excreting excess salt found in seabirds, located above or in front of the eye
![salt gland](images_gloss/salt gland d28-1-050.jpg )
salt gland     
sap well
A hole drilled in bark by a sapsucker that allows sap to collect. The woodpecker returns periodically to the well to drink the sap and eat any insects attracted to it.
![sap well](images_gloss/Yellow-bellied Sapsucker m50-8-045.jpg )
Yellow-bellied Sapsucker      Sphyrapicus varius
scapula
The shoulder blade
![scapula](images_gloss/scapula d28-1-051.jpg )
scapula     
scapulars
Feathers at the base of the wing lying at the side of the back and often covering the folded wing
![scapulars](images_gloss/Greater Flamingo m17-68-090.jpg )
Greater Flamingo      Phoenicopterus roseus
scavengers
Animals that feed on dead and decaying plants and animals
![scavengers](images_gloss/White-backed Vulture k01-39-054.jpg )
White-backed Vulture      Gyps africanus
scleral ossicles
A ring of bones that supports the eye
![scleral ossicles](images_gloss/scleral ossicles d28-1-052.jpg )
scleral ossicles     
scrape
A shallow depression in the ground made by a bird to use as a nest
![scrape](images_gloss/Least Tern t16-2-039.jpg )
Least Tern      Sternula antillarum
secondaries
Flight feathers that attach to the ulna (forearm) inward from the primaries
![secondaries](images_gloss/Steller's Eider f20-11-390.jpg )
Steller's Eider      Polysticta stelleri
slots
Spaces between the primary feathers of certain birds such as vultures that allow individual feathers to act as airfoils and reduce turbulence
![slots](images_gloss/Turkey Vulture b57-1-283.jpg )
Turkey Vulture      Cathartes aura
soaring
Sailing on outstretched wings without flapping or losing altitude
![soaring](images_gloss/Bald Eagle t08-13-039.jpg )
Bald Eagle      Haliaeetus leucocephalus
songs
Complex vocalizations communicating territoriality or advertising for a mate
![songs](images_gloss/Blue-winged Warbler s79-2-008.jpg )
Blue-winged Warbler      Vermivora pinus
speculum
A patch of bright feathers on the secodaries of certain ducks' wings
![speculum](images_gloss/Mallard m17-21-054.jpg )
Mallard      Anas platyrhynchos
spread-wing posture
Perched stance with wings outspread
![spread-wing posture](images_gloss/Double-crested Cormorant l07-46-046.jpg )
Double-crested Cormorant      Phalacrocorax auritus
spur
A bony spike on the wing or tarsus certain birds, such as jacanas, screamers, pheasants, and spurfowl
![spur](images_gloss/Yellow-necked Spurfowl m47-14-165.jpg )
Yellow-necked Spurfowl      Francolinus leucoscepus
sternum
The breastbone - the site of attachment for the major flight muscles and the ribs
![sternum](images_gloss/sternum d28-1-053.jpg )
sternum     
structural colors
Coloration resulting from light scattering due to the physical structure of feathers
![structural colors](images_gloss/Magnificent Hummingbird r25-13-034.jpg )
Magnificent Hummingbird      Eugenes fulgens
subadult
A bird past the juvenile stage that has not reached maturity
![subadult](images_gloss/Bald Eagle c22-38-043.jpg )
Bald Eagle      Haliaeetus leucocephalus
sunning
Posturing to catch solar radiation
![sunning](images_gloss/Groove-billed Ani g25-1-030.jpg )
Groove-billed Ani      Crotophaga sulcirostris
supracoracoideus
The muscle that powers the upstroke of the wing. It attaches to the sternum and the humerus.
![supracoracoideus](images_gloss/supracoracoideous d28-1-054.jpg )
supracoracoideous     
surface diving
Diving beneath the water, starting at a swimming position
![surface diving](images_gloss/Horned Grebe c22-35-126.jpg )
Horned Grebe      Podiceps auritus
syndactyl feet
Feet with the outer and middle toes fused for most of the length, such as in kingfishers and hornbills
![syndactyl feet](images_gloss/Rufous Hornbill w02-16-134.jpg )
Rufous Hornbill      Buceros hydrocorax
syringeal muscles
Muscles that modulate the voice by controlling the shape of the syrinx (avian voice box)
![syringeal muscles](images_gloss/syringeal muscles d28-1-055.jpg )
syringeal muscles     
T     
tarsometatarsus
The outermost of the three long leg bones in a bird. It is homologous to ankle and foot bones of mammals.
![tarsometatarsus](images_gloss/tarsometatarsus d28-1-056.jpg )
tarsometatarsus     
tarsus
Alternate name for the tarsometatarsus and also for that region of the leg
![tarsus](images_gloss/Herring Gull m17-23-126.jpg )
Herring Gull      Larus argentatus
temporal fovea
An area of concentrated receptor cells in the retina toward the side of the head. It increases the depth perception in hawks, terns parrots, swallows and doves.
![temporal fovea](images_gloss/temporal fovea d28-1-057.jpg )
temporal fovea     
territory
A space defended by a bird for the exclusive use
![territory](images_gloss/Yellow-headed Blackbird m17-67-921.jpg )
Yellow-headed Blackbird      Xanthocephalus xanthocephalus
tibiotarsus
The middle bone of the three long bones of the leg, familiar to us as the drumstick
![tibiotarsus](images_gloss/tibiotarsus d28-1-058.jpg )
tibiotarsus     
torpor
A state of severely decreased metabolism, in which the body temperature of a bird is reduced and energy is conserved
![torpor](images_gloss/torpor d28-1-059.jpg )
torpor     
totipalmate
All four toes joined in a web; typical of pelicans, boobies, and cormorants
![totipalmate](images_gloss/Blue-footed Booby l07-40-027.jpg )
Blue-footed Booby      Sula nebouxii
tubular nares
A cylindrical extension of the nostrils in Procelliform seabirds, which helps to expel briny secretions of the salt gland
![tubular nares](images_gloss/Southern Giant-Petrel a25-1-047.jpg )
Southern Giant-Petrel      Macronectes giganteus
tympanic membrane
The eardrum
![tympanic membrane](images_gloss/Double-wattled Cassowary s66-3-001.jpg )
Double-wattled Cassowary      Casuafalcorius casuarius
U     
ulna
Larger of paired bones between the humerus and the wrist, to which secondaries attach
![ulna](images_gloss/ulna d28-1-060.jpg )
ulna     
undertail coverts
The ventral feathers covering the base of the retrices
![undertail coverts](images_gloss/Dusky Grouse n10-22-027.jpg )
Dusky Grouse      Dendragapus obscurus
underwing coverts
The ventral feathers covering the base of the remiges
![underwing coverts](images_gloss/Willet s36-31-084.jpg )
Willet      Catoptrophorus semipalmatus
uppertail coverts
The dorsal feathers covering the base of the retrices
![uppertail coverts](images_gloss/Mew Gull p34-2-282.jpg )
Mew Gull      Larus canus
uric acid
A pasty white excretory product equivalent to urine, but less wasteful of water
![uric acid](images_gloss/Atlantic Puffin b57-16-052.jpg )
Atlantic Puffin      Fratercula arctica
uropygial gland
The preen gland located near the dorsal base of the tail, which secretes oily substances to protect the feathers
![uropygial gland](images_gloss/American Redstart c22-44-040.jpg )
American Redstart      Setophaga ruticilla
V     
vane
The sides of the feather extending from the shaft
![vane](images_gloss/Wood Stork f26-4-080.jpg )
Wood Stork      Mycteria americana
vent
The opening of the cloaca
![vent](images_gloss/Chipping Sparrow n10-25-019.jpg )
Chipping Sparrow      Spizella passerina
vitelline membrane
The thin layered structure around the egg yolk, which following fertilization forms a barrier to new spermatozoa
![vitelline membrane](images_gloss/vitelline membrane d28-1-061.jpg )
vitelline membrane     
W     
wing bar
A stripe formed on the wing by light-colored tips to coverts
![wing bar](images_gloss/Blackpoll Warbler c22-44-043.jpg )
Blackpoll Warbler      Setophaga striata
wing spurs
Sharp bony projections on the wings of certain birds such as jacanas, screamers and some plovers
![wing spurs](images_gloss/Horned Screamer b57-17-057.jpg )
Horned Screamer      Anhima cornuta
wingspread
The distance from one wingtip to the other
![wingspread](images_gloss/Bald Eagle c22-35-020.jpg )
Bald Eagle      Haliaeetus leucocephalus
wrist
The bend in the wing at the base of the primary feathers where the outmost segment of the wing starts--rusty-colored in this Great Blue Heron
![wrist](images_gloss/Great Blue Heron l07-46-058.jpg )
Great Blue Heron      Ardea herodias
X     
     
yolk
The yellow part of the egg which feeds the developing embryo. These men are cooking an ostrich egg.
![yolk](images_gloss/Common Ostrich k01-36-002.jpg )
Common Ostrich      Struthio camelus
Z     
zygodactyl feet
A foot in which the hallux and fourth toe face backward and second and third to face forward, as in woodpeckers and parrots
![zygodactyl feet](images_gloss/Checker-throated Woodpecker w02-48-115.jpg )
Checker-throated Woodpecker      Picus mentalis
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