GLOSSARY

This glossary comprises terms that apply specifically to Bald Eagles. It is not intended to be a comprehensive glossary for birds, although many of the terms apply to many birds (e.g. “cere”), most birds (e.g. “crop” ), or all birds (e.g. “hypothalamus”). For some terms I have provided an etymology (linguistic origins), which is one of my favorite things, but it also may shed light on why scientists use that particular term. Many entries include more than a definition, but also more details than would be found in a dictionary.

All of the entries are my work, although naturally I have relied on many sources (most of them found in lists of References throughout this website) to guide my definitions and explanations. As with everything else on this website, I own the copyright to all of the entries, except where specifically noted and credited. If you copy any text to share, please put quotation marks (” “) around the text and give a link to my website (www.elfruler.com).

This is a work in progress — I continue to add new terms. If you do not find a term here that you would like me to add, please contact me.

Click on photos to enlarge.

tissue in the that produces 2 types of steroid hormones: glucocorticoids that regulate the body's energy use, especially in response to stress, and mineralcorticoids that regulate salt/water balance in the body

paired glands in the abdominal cavity above the top lobe of the kidneys; 2 types of adrenal tissues which are intermingled, the and the , produce different types of hormones to regulate energy flow, especially in stressful situations, salt/water balance, and responses to stress

tissue in the that produces neurohormones to regulate the body's response to emergency situations, acting almost instantaneously

hormone that manages the body's response to stress by activating release of hormones from the ; secreted by the of the ; abbreviated

collection of water, proteins, and some carbohydrates, lipids, and minerals that surround the and to nourish the growing , provides cushioning as the is moved around in the , helps hold the internal temperature of the when parents are not tightly incubating; accumulates in layers during the 's journey through the : in the a thin layer of viscous (dense) materials, including the (stringy strands extending out from the and connecting to the , suspending the developing and the in the ), in the magum a thin watery layer and a thick viscous later (the largest proportion of ), in the another thin watery layer; more fluid added in the , referred to as "plumping"; shrinks as water and proteins are absorbed by the and water is evaporated through the

hormone that helps raise blood pressure and blood salt level, stimulating the hormone from the kidneys to enhance reabsorption of sodium; a hormone secreted by the ; abbreviated

extra-embryonic membrane surrounding the , , and ; performs exchange of carbon dioxide from the and oxygen from outside the , and collects wastes from the ; develops out of the gut of the about 5-7 days into incubation, connected via blood vessels through the abdominal wall to the heart; about halfway through incubation it fuses with the to form the

to the feathers of another bird, especially on the head & other places that the other eagle cannot reach; may serve a bonding purpose; Greek allos = other

referring to species whose newly hatched chicks are at the low end of a spectrum of physiological development; closed eyes, few motor skills and limited strength and coordination, sparse or absent , unable to thermoregulate, and fully dependent on parents for feeding, warmth, and protection for a long period before leaving the nest (); includes songbirds, parrots, and woodpeckers; Latin altrix = female nourisher

first of the () on the wing (sometimes labeled the

second , as homologous to the human index ); also called the or ; 4 attach to it by ligaments and tendons, and sometimes are referred to collectively as the ; the bone moves to lift and lower the to help control air flow across the top of the wing in flight, especially to prevent a stall; photo © Idaho Virtual Museum as licensed by Creative Commons

feathers attached to the () of the wing; Bald Eagles have 4 ; sometimes called alular quills

extra-embryonic membrane surrounding the , filled with fluids, some nutrients, and proteins absorbed from ; floats in the amniotic fluid, which keeps it moist, protected, and cushioned and allows it to move and grow; has muscles that gently contract to prevent the parts of the from adhering to each other; develops along with the out of the ectoderm and mesoderm (germ layers that develop into epidermis, muscles, blood vessels, and organs) in the gut area of the about 4 days into incubation, expands around and behind the , fully surrounding it about a third of the way into incubation; chick swallows remaining amniotic fluid before hatch

hormone that helps raise blood pressure; secreted by the liver; abbreviated

at or toward the front or head of the body; in contrast to ; also

lobe of the that releases hormones to regulate processes of the gonads, , thyroid, , and stomach

antidiuretic hormone that raises water concentration in the blood by inducing the kidneys to absorb and conserve water; during production it relaxes the and induces uterine contractions; secreted by the to the of the to be stored and released when needed; abbreviated

hatching of eggs in a one by one over a period of time, usually a few days; the eggs hatch in the order they were laid; the time between hatches can be shortened by which slows down development of the first or eggs laid; less common than ; includes Bald Eagles and other raptors, herons, egrets, cranes, and parrots; see

hormone secreted by the heart to act as a diuretic to decrease blood salt and blood pressure; also secreted by the to inhibit secretion of other adrenal hormones; abbreviated

feathers in the

upper and lower jaws of a bird; bone with a layer of tissue with blood vessels and nerves, and sheathed by a thick hard covering of beta-keratin, which is harder than the alpha-keratin found in mammals; both upper and lower jaws move as the opens and closes, unlike in humans whose is fixed as it is fused with the skull; also ; see and

in ornithology, a particular shape of a bird's nest; in reference to Bald Eagles, used to mean the interior of a basin-shaped nest surrounded by a perimeter of sticks, usually lined with grasses and other soft materials to cradle eggs and nestlings; often used to refer to the small indentation where eggs are laid (see ); sometimes spelled "," an archaic Old English (pre-Shakespeare) and Germanic spelling for a basin; most sources on Bald Eagle nests use the modern spelling "" (e.g. M.V. Stalmaster The Bald Eagle, p. 53; American Eagle Foundation), while the earliest usage with the archaic spelling "" seems to have appeared on the internet in the late 1990s

when an eaglet flies or steps onto a branch of the nest tree outside of the nest and perches there

short feather with a stiff shaft, no vanes, and few or no barbs; found on parts of the head

1. noun: collection of all the hatched young in a single breeding cycle of a mated pair until they ; 2. verb: to protect young hatchlings from weather and predators by covering them with the body, especially the wings

patch of featherless skin on the abdomen that develops in incubating adults; the region sheds its downy feathers (not the overlying , whose follicles in Bald Eagles are well to the side), tissues accumulate fluids, and blood vessels swell in size and number (vascularization); parents wiggle to spread the apart to expose the warm bare skin to the eggs and young chicks; the patch transfers heat to the eggs, and sensitized nerves enable the parents to detect the temperature of the eggs so they can modify their posture to optimize heat transfer; hormones (estrogens, , and ) induce development of the beginning a few days before ; de-feathering is nearly complete at , while full vascularization occurs a few days later; sometimes called ; see Reproduction and Hormones; photo © Thomas Demma

hormone that lowers excessively high blood calcium by removing it from the blood and depositing it in the bones; declines after to allow calcium to rise in the for production; secreted by the ; abbreviated

part of the or of the wing; fusion of the 6 carpal () bones together with the 4 metacarpal () bones, a

shape that gives the bone strength and stability; the wing digits are connected to the end, together forming the or ; feathers P1-P6 attach to the by ligaments and tendons; photo © Idaho Virtual Museum as licensed by Creative Commons

to regurgitate a , or , a wad of indigestible material produced in the ; see

at, of, or toward the tail; also ; Latin cauda = tail

thick dense membraneous band at the base of the , of softer keratin than the hard covering of the part of the ; surrounds the nostrils

2 fibrous protein strands produced with the first layer in the , extending out from the and connecting to blunt and pointed ends of the ; they suspend the developing and the in the and enable the to rotate freely so that the lighter-weight always floats to the top above the ; they are part of the layer of laid down in the ; Greek khalaza = small knot

extra-embryonic membrane surrounding the , , and , attached to the inner ; fusion of the and membranes about halfway through incubation; connected to the via blood vessels to the heart through the abdominal wall; performs exchange of carbon dioxide from the and oxygen from outside the , and collects wastes from the ; by the chick triggers its lungs and air sacs to begin functioning, the respiratory action of this membrane recedes and it dries up; it remains attached to the at hatch and disconnects from the chick at the umbilicus; if the is broken before the and this membrane is pierced, it can damage its blood vessels and interrupt its respiratory function before the chick's lungs are ready to take over that function; abbreviated

extra-embryonic membrane surrounding the , , , , and ; performs exchange of carbon dioxide from the and oxygen from outside the , and collects wastes from the ; develops along with the out of the ectoderm and mesoderm (germ layers that develop into epidermis, muscles, blood vessels, and organs) in the gut area of the and extends around the , then (unlike the ) it doubles back to expand out around the and and attaches to the inner ; about halfway through incubation it fuses with the to form the

referring to the daily oscillation between sunlight and darkness caused by the earth's revolution around the sun

referring to the yearly cycle of changes from one season to the next caused by the earth's revolution around the sun and rotation on its axis

cavity at the end of the digestive tract that receives feces, , and eggs and for expulsion from the body; its upper section receives digestive wastes (feces) from the intestines; the middle section receives nitrogenous metabolic wastes () from the kidneys, and eggs and from the gonads; feces and are expelled together; a female eagle may "clear the ," or expel any wastes a few minutes before laying an ; Latin cloaca = drain

collection of all the eggs laid in a single uninterrupted reproductive cycle of a mated pair; see also second

Central Nervous System

corner of the mouth, the point where the soft keratin of the ricti of the (upper ) and (lower ) meet

vaned feathers covering the body, including the flight feathers on the wings and tail; covers the downy feathers; so called because it gives the body its shape or contour

hormone that optimizes the body's use of energy, especially in response to stressful events or circumstances, acting on other hormones, organs and glands, muscles, the circulatory, digestive, reproductive, and immune systems; a hormone secreted by the ; abbreviated

type of hormone that stimulates the to produce its hormones; includes (Greek tropos = change, reaction)

hormone that initiates hormonal and metabolic responses to stressful events or circumstances; secreted by the ; abbreviated

feathers arranged in rows to cover the bases of the flight feathers of the wing and tail

of, at, or toward the head; also ; Greek kranion = skull

expandable section at the low end of the where food can be stored for a time after it is swallowed before it is pushed by contracting muscles into the upper stomach (); enables birds to ingest more food than they need immediately; no digestion occurs in the ; found in raptors, grouse, some songbirds (especially seed-eaters), pigeons, and doves; falconers have referred to the neck-stretching, gyrating, downward-pushing action of moving the food out of the to the stomach as "putting over"; " milk" produced by pigeons and doves (but not raptors) consists of nutrient-rich cells from the lining of the that are regurgitated to feed young

curved downward (as a raptor's or )

practice of postponing incubation until the last or next-to-last in a has been laid; suspends development of the earlier embryos so that once incubation begins all embryos develop at the same rate and the eggs hatch synchronously; includes ducks, geese, shorebirds, most songbirds, woodpeckers, and poultry; often applied to Bald Eagles and other raptors, somewhat misleadingly since usually these do incubate the earlier eggs at least part of the time, and their eggs hatch asynchronously; see

toe extending from the () or finger extending from the () of the wing; the digits are extensively fused in most birds; Bald Eagles have 4 digits on each foot: first (back or with 2 ), second (inner with 3 ), third (middle with 4 ), and fourth (outer with 5 ); the on each is the ; Bald Eagles have 3 digits on each hand: first (the , or the or , with 2 fused ; sometimes labeled the first ), second (major , with 2 fused + 1 unfused , which articulates to help raise and lower the feathers in flight; sometimes labeled the third ), and third (minor , below the second , with 1 , sometimes labeled the fourth ); 3-D image of the digits of ; feather P7 attaches to the third and P8-P10 attach to the second , by ligaments and tendons

further from the center of the body or from a structure's beginning point; e.g. "the is the joint at the end of the femur" or "the toes are to the "; "the is to the base of the "; in contrast to

active primarily during daylight hours, e.g. eagles and hawks, who hunt and migrate in the daytime

on the back or the top side of the body or a part of the body; in contrast to ; Latin dorsum = back

1. of a female (ovum) that is not yet fertilized; or 2. a hard ovoid (oval-shaped) which may or may not contain a fertilized with its , , and membranes

small indentation in the center of a Bald Eagle nest where eggs are laid and incubated and new eaglets are brooded by the parents until the chicks outgrow the space; generally a few inches in diameter and 4-8 inches deep; usually lined with soft grasses, leaves or fronds, and other soft materials; not always present; also and sometimes

hard beta-keratin pointed growth on the tip of the upper () of a hatchling, helps break the during hatching; also called the ; begins to develop about a third of the way through the incubation period, and gradually wears off after hatch

a fertilized during growth and development up to hatching

referring to the secretion of hormones internally in the body via the bloodstream and/or the central nervous system, targeting cells that have receptors for a particular hormone and resulting in a change of behavior or physiological state; in distinction to exocrine, secreting substances outside the body (Greek endon = within + krinein = to choose or distinguish); see Avian System

internal or inside the body; Greek endo = within + genous = produced

neurohormone, sometimes called , that responds rapidly to stressful events and circumstances, increasing metabolism, blood sugar and fat, blood pressure, neural activity in the brain, and muscle function; dampens reproductive activities; secreted by the ; abbreviated

moment when the Earth's axis is tilted neither toward nor away from the sun, which is thus exactly overhead at the equator, and day and night are of roughly equal duration; happens twice a year, on ~ March 20 (vernal or spring ) and ~September 22 (autumnal ) in the northern hemisphere; Latin equus = equal + nox = night

hormone that stimulates production of red blood cells; secreted by the kidneys; abbreviated

upper tube of the digestive system where food goes when swallowed; glands secrete fluids to moiston the food, and muscles in the lining move food down toward the for digesting; the lower portion of the is expandable to form the where food is stored if not needed immediately

an hormone, induces nest-building, gonadal , development of the , synthesis, maturation of ovarian follicles, calcium metabolism for production, and production; secreted by the and ; abbreviated

external or outside the body; Greek exo = outside + genous = produced

first break by the chick through the hard to begin hatching, a tiny crack or hole that gradually grows as the chick pecks with its and pushes against the with neck, head, and legs

, , , and , 4 thin layers of tissue that grow out from the (in contrast to , which are added to the from the of the female) to serve different functions; the and fuse to become the about halfway through incubation; see entries on each term

to rub the against a hard surface, usually a limb or trunk of a tree; cleans the after eating, and helps keep the keratin outer layer of the in good condition with the proper length, width, thickness, and overall shape

long thin leg bone extending down from the joint, along the lateral (outer) side of the , narrowing significantly and fusing to the just above the (); photo of on the lateral side of the , © Idaho Virtual Museum as licensed by Creative Commons

1. noun: first flight out of the nest tree by the grown eaglet; sometimes used to mean the point at which a young bird's flight feathers are fully developed and it is capable of flying, whether it has left the nest or not; 2. verb: to fly out of the nest tree for the first time as an eaglet

breeding-age eagle who is unmated and has no claim on a territory or nest, free to travel and may challenge established pairs and nests

hormone that induces gonadal , release of gonadal hormones, production, maturation of ova, deposition, , and lipid metabolism; stimulates nest-building; secreted by the of the ; abbreviated

see

bottom of the from the end of the middle to the end of the , not including the talons

a mature female or male sex cell, an unfertilized or a cell (spermatazoan), with a single set of chromosomes (haploid) ready to be joined with a of the opposite sex (fertilization); the union of the 2 gametes creates a , a fertilized cell with a full set of paired chromosomes (diploid); in birds, the female is heterogametic, with dissimilar ZW sex chromosomes, the male is homogametic, with similar ZZ sex chromosomes, so the female provides either the male or the female chromosome and thus determines the sex of the —the opposite of the case in mammals

the gap between the (upper ) and (lower ) at the (corner of the mouth) when the is open

hormone that helps lower fat levels; secreted by the stomach; abbreviated

lower section, or , of the stomach; regular, strong muscular contractions grind any food items that have not been broken down in the and move the digested material toward the intestines; the muscles also compress indigestible matter into which eventually are pushed back up through the and to be regurgitated

hormone that causes the liver to break down lipids and muscle protein to release energy, increases blood sugar, and regulates heat production in cold weather; secreted by the ; secreted by the ; abbreviated

type of steroid hormone secreted by the that regulates glucose levels for adequate energy flow; includes and cortisol

reproductive organ that produces gametes, the and ; produces and secretes estrogens, androgens, and

type of hormone that stimulates the gonads to produce their hormones; includes and ; Greek tropos = change, reaction

hormone that inhibits the from secreting hormones that would stimulate the gonads to release their hormones; a neurohormone secreted by the ; abbreviated

hormone that stimulates the to secrete hormones that stimulate the gonads ( and ) to release their hormones; a neurohormone secreted by the ; abbreviated

hormone that stimulates growth, development, metabolism, and fat and protein synthesis in embryos and young birds; secreted by the of the ; abbreviated

hormone that stimulates secretion of hormones for growth, metabolism, and developing in young birds; low concentration in adults; secreted by the ; abbreviated

scientific designation for "Bald Eagle," following the two-part naming system (binomial nomenclature) in , which assigns a unique and internationally recognized name to each biological species; the first word refers to the genus and the second word refers to the species; the designation can be traced back to 18th-century naturalist Carl Linnaeus; pronounced hal-ee-uh-EE-tus LOO-co-SEF-uh-lus (pronunciation guide ; Greek halia = of the sea + aetos = eagle, leuco = white + cephalos = head

the back , or first , of the ; has 2 counting the

see

small region of the forebrain in front of the optic lobe; functions with the to maintain the body's daily () rhythms and synchronize them with the rhythms of the Earth; receives and processes information from the environment and directs the body's systems to respond appropriately; secretes neurohormones to the to trigger release of hormones for reproduction, growth and development, salt/water balance, and responses to stress

learning process whereby a newly hatched eaglet follows and responds to the movements and sounds of its parents as it depends on them for food, warmth, and protection, and learns to mimic and identify with them and, by extension, with their species; on the parents occurs within the first couple of weeks after hatch; on humans can occur if a bird spends its earliest days in contact with humans in the absence of its parents, which can interfere with critical behavioral development; habitat begins to develop as the eaglet is able to observe its surroundings, later leading to a return to its natal territory after fledging

1. referring to an adult who is unable to produce ova or , whether because it is not the season of reproduction and the gonads are regressed and incapable of producing gametes, or due to circumstances that suppress the reproductive process such as trauma or disturbance, or ; or 2. referring to an that has not been fertilized by , and hence an that will not hatch

top section of a female's , a muscular structure whose opening expands like the mouth of a funnel and envelops the mature as it emerges from the ; here the cell undergoes one final division to become a haploid , fertilization by occurs (if available and viable), and the outer layer of the (extravitelline membrane) surrounds the with its ; once this membrane is in place fertilization is impossible because can't penetrate it; a thin layer of is laid down over the , including the , thick twisted strands extending out from both ends of the that eventually fuse to the hard , suspending the and in the in the center of the but allowing to rotate freely so that the always floats to the top above the heavier ; Latin infundibulum = funnel

hormone that complements during maturation and ; may help stimulate parental behavior; secreted by the and the ovarian follicles; abbreviated

hormone that helps build muscle protein, decreases blood sugar, increases blood fat protein synthesis, and lipids, and helps regulate heat production in cold weather; in embryos stimulates metabolism and growth; secreted by the ; abbreviated

practice of incubating earlier eggs of a part of the time until all eggs are laid; slows down development of the earlier embryos so that the eggs hatch more closely together, although never synchronously; includes Bald Eagles and other raptors, herons, egrets, cranes, and parrots; among most species the time spent incubating increases as more eggs are laid, which along with the point at which full-time incubation starts varies among species and breeding pairs (many falcon species postpone full-time incubation until the next-to-last is laid, but their eggs still hatch asynchronously); perhaps a better term than "" for Bald Eagles and other raptors, since these parents do incubate earlier eggs at least part of the time, and their eggs hatch asynchronously

piercing by a chick of the inner a day or two before the chick begins to hatch out of the ; gives access to the air cell between the inner and outer and prompts lungs and air sacs to begin functioning

joint between the () and the (lower leg bone), also called the or ; comparable to the human ; so called because of its location between the upper and lower tarsal bones; sometimes mistakenly called the , which in birds is the joint between the (lower leg bone) and the femur (thighbone) and is usually buried in body feathers

short section of a female's between the and the where a final layer of is added and the 2 (inner and outer) are formed around the , , and ; these are then pushed into the to receive the hard ; Greek isthmos = narrow passage

used as an adjective on this website: referring to traits of an eagle in its 12 months

used as a noun on this website: an eagle in its first 12 months

joint between the femur (upper leg or thighbone) and the (lower leg bone); protected by the patella as in humans; usually hidden under feathers and wings

the cycle of physiological changes, behaviors, and processes that are fundamental to the survival of a species and of individuals in the species, repeated annually in most species; includes reproduction, molt, and in many species, migration; for Bald Eagles includes reproduction and molt, and for some individuals, migration or more limited movement away from the breeding range; also called or ; see Life History

hormone that induces gonadal , production, maturation of ova, deposition, , and lipid metabolism; secreted by the of the ; abbreviated

largest section of a female's , between the and the ; site where most of the forms around the ; Latin magnus = large

of the ; long open triangular shape with a short fused section at the tip; in Bald Eagles narrower than the which surrounds its sides when the is closed; articulates dorsally with the same bone (the quadrate) that moves both the and the to open and close the ; bone is covered by a layer of tissue with blood vessels and nerves, and sheathed on the lower side by a thick hard covering of beta-keratin, which is harder than the alpha-keratin found in mammals; photo from (underneath) side © Idaho Virtual Museum as licensed by Creative Commons

to spread the wings and hunch over food to prevent stealing by another bird, including a sibling or a parent

to spread the wings and crouch over food to lay claim or prevent stealing by another bird, including a parent or sibling; sometimes a defensive posture if startled; among Bald Eagles, often accompanied by loud, threatening vocalizing; sometimes used as a noun

, the portion of the wing; comprised of the

(fused carpal and metacarpal bones) and 3 digits with several fused ; the 10 feathers attach to the by ligaments and tendons; composite of images © Idaho Virtual Museum, my labels added, as licensed by Creative Commons; 3-D image of the wing bones including the

of the ; not fused to the skull as in humans, but articulates (forms a joint) with it dorsally behind the (in Bald Eagles), forming a hinge so that the can move upward; extends under the skull with the palatine (forming the palate) and the jugal arch, which articulates below the ear with a bone (the quadrate) that also articulates with the lower (), opening and closing both lower and upper bones simultaneously; bone is covered by a layer of tissue with blood vessels and nerves, and sheathed on top by a thick hard covering of beta-keratin, which is harder than the alpha-keratin found in mammals; sometimes called the upper ; photo of skull © Idaho Virtual Museum (lower not shown), my labels added, as licensed by Creative Commons;

hormone that regulates the body's and rhythms; a neurohormone secreted by the ; abbreviated

hormone that stimulates the hormone to induce uterine contractions; also helps lower blood pressure by inhibiting a hormone from the ; secreted by the to the of the to be stored and released when needed; abbreviated

type of neurohormone secreted by the that helps maintain an optimal salt/water balance and blood pressure in the body; includes

breeding situation that involves 1 female and 1 male; does not necessarily preclude extra-pair copulation (EPC) by one or both members of a pair, or even instances where 1 member is actively involved in concurrent breeding attempts at 2 nests, both of which have been observed among Bald Eagles

1. verb: to expel wastes from the body through the ; 2. noun, pl. mutes: expelled wastes; falconry term; Old French muetir = to defecate

old word for nostrils, sometimes used by falconers for the opening of the nasal passage in the ; sing. naris; Latin naris = nostril

the thin layer of downy (plumulaceous) feathers present on an eaglet at hatch; pushed out by the growing from the same follicles, beginning in the second week after hatch

thin translucent membrane that closes over the cornea of the eye

from front to back; cleans, lubricates, and protects the eye from debris; sometimes called the third or (screen capture, CA Sauces Canyon, 3/11/24, © Institute for Wildlife Studies; see video)

referring to species whose young are not well developed at hatch and must remain in the nest for a long period while they are cared for by parents; see also and ; Latin nidus = nest + colere = to inhabit

referring to species whose young are well enough developed to be able to leave the nest shortly after hatching; see also preocial; Latin nidus = nest + fugere = to flee

active primarily during nighttime hours, e.g. owls, who have sensory adaptations that enable them to hunt in the dark

referring to an that fails to develop properly during incubation and is incapable of living; also , rotten, addled; Latin vivere = to live

hormone, sometimes called , that responds rapidly to stressful events and circumstances, increasing metabolism, blood sugar and fat, blood pressure, neural activity in the brain, and muscle function; dampens reproductive activities; also plays a role in regulating rhythms in the brain; a neurohormone secreted by the ; abbreviated

female germ cell; formed in the where it accumulates materials from the liver as it approaches into the ; in the the and are surrounded by 2 thin membranes, the (oolemma) and the perivitelline membrane; occurs when the follicle ruptures to allow the and its to enter the of the , where it can be fertilized by

sac in the that produces a germ cell () and collects materials from the liver for the and releases them to the for fertilization by ; follicles mature in a hierarchy, with the most mature (labeled F1) first in line to ovulate

female reproductive organ, in the abdominal cavity next to the top lobe of the kidneys; inner area () is connective tissue with blood vessels and nerves, outer layer () is made up of follicles each of which produces a germ cell (); follicles collect materials from the liver for the and release them to the for fertilization by ; secretes hormones that stimulate courtship behaviors, development of the , gonadal , production of ova and of materials for and , and calcium production for shells, and that help regulate the timing of ; most birds, including Bald Eagles, have only the left (and ), the right being absent or vestigial

reproductive tract of a female bird, extending from the to the just above the ; the walls of the are lined with muscles that move an through from the at the top to the ; the has several sections with discrete functions: the which receives an from the and fertilized by (unless there are no viable available); the magum where the is surrounded by ; the where the are wrapped around the ; the (or ) where the hard calcium carbonate is formed; and the from which the is pushed into the just prior to laying; most birds, including Bald Eagles, have only the left (and ), the right being absent or vestigial

producing ova (eggs) that are expelled from the mother's body encased in a in which the embryos develop until they hatch; Latin ovum = + parus = producing; distinct from viviparous, Latin vivus = living + parus = producing

the process of laying an (Latin ovum = + positio = placing or depositing)

the release of a female's , the unfertilized or , from the most mature follicle of the to the of the where it can be fertilized by from a male

unfertilized female sex cell; can refer to a that has divided by meiosis to become haploid (reduced to one set of chromosomes instead of the full diploid number) and is ready for fertilization, or to an or germ cell before it divides by meiosis; sometimes called an

gland in the duodenal loop of the intestines, secretes hormones to regulate glucose levels, metabolism, and protein and lipid synthesis

multi-lobed gland at the base of the neck adjacent to the thyroid, secretes a hormone that raises blood calcium

hormone that raises low blood calcium by stimulating the kidneys to reabsorb calcium so it is not excreted and by activating vitamin d to induce bones to release calcium into the blood; increases after to aid in production in the ; secreted by the parathyroid gland; abbreviated

percentage of time a parent incubates eggs after regular incubation of a has begun, in relation to periods of inattentiveness or not incubating; can vary with species, sex, climate, weather, disturbances, etc.; Bald Eagles and other as well as birds, tend to have a lower percentage of attentiveness than birds, although still quite high

compact wad of indigestible matter left over after the has ground food that has not been broken down in the ; pushed up the to be regurgitated (or ""); in Bald Eagles includes fur, scales, feathers, and teeth, but not most bones, which Bald Eagles can digest; Bald Eagles expel a about once per day, typically in the morning, and not always correlated with a particular meal; also

one of the bones of a on the wing or ; the on each is the ; pl.

the timespan of sunlight within a 24-hour day; Greek phos = light

tiny gland located at the top of the brain between the cerebral hemispheres and the cerebellum; comprises specialized neural cells that function as photoreceptors that detect the daily oscillation between sunlight and darkness; functions with the as an oscillator to keep the body's internal daily () rhythms of activity and rest; secretes into the bloodstream during nighttime hours, communicating the daily changes in the length of daylight (the ) to keep the body's rhythms in synchrony with the Earth's daily rhythms; see Photoperiodism and Reproduction Timing

1. internal pip: piercing by a chick of the inner a day or two before the chick begins to hatch out of the ; gives access to the air cell between the inner and outer and prompts lungs and air sacs to begin functioning; 2. external pip: first break by the chick through the hard to begin hatching, a tiny crack or hole that gradually grows as the chick pecks with its and pushes against the with neck, head, and legs

see

gland at the base of the brain immediately below the ; 2 discrete regions, the and the ; called the "" because its hormones regulate the release of downstream hormones that are involved in myriad bodily functions, including reproduction, growth and metabolism, salt/water balance and blood sugar regulation, stress responses, feather growth, molt, and migration

breeding situation that involves 1 female and 2 or more males; pronounced POL-ee-an-dree; rarely observed among raptors; Greek polus = many + andros = husbands; see What Is Cooperative Breeding?

general term for a breeding situation that involves at least 3 adults; rarely observed among raptors; Greek polus = many + gamos = marriage; see What Is Cooperative Breeding?

breeding situation that involves 2 or more females and 2 or more males; pronounced pol-ee-JIN-an-dree; rarely observed among raptors; Greek polus = many + gynous = wives + andros = husbands; see What Is Cooperative Breeding?

breeding situation that involves 2 or more females and 1 male; pronounced puh-LIH-juh-nee; rarely observed among raptors; Greek polus = many + gynous = wives; see What Is Cooperative Breeding?

at or toward the back or tail of the body; in contrast to ; also

lobe of the that receives and stores 2 hormones from the for later release, both activated to induce uterine contractions when an is ready to be laid

referring to species whose newly hatched chicks are at the high end of a spectrum of physiological development; eyes open, some motor skills (walking and swimming), significant covering of and at least partly able to thermoregulate, some motor skills (walking and swimming), only partly dependent on parents for care, quick departure from the nest (), and some ability to acquire food; includes geese, ducks, swans, shorebirds, and poultry; Latin praecox = early maturing

to groom the feathers with the by grasping one near their base and sliding the out to its tip; removes grit and parasites and helps interlock the barbs and barbules on the vanes if they have become misaligned; often the eagle gathers oil from the uropygial () gland at the base of the tail and spreads the oil on the feathers as it preens; the oil helps condition the feathers but does not waterproof them; eaglets begin in their second week when emerge, helping break up the feather sheath at the mouth of the follicle and align the barbs and barbules as the vanes unfurl

the 10 long flight feathers at the outer () part of each wing; provide forward thrust and help control direction in flight; numbered P1-P10; P1-P6 are attached to the , P7-P10 are attached to the second and third digits extending from the

hormone that stimulates nest-building, aids in development of the , may trigger release of stored to be fertilized, helps trigger and uterine contractions by stimulating other hormones; secreted by the and ; abbreviated

hormone that regulates parental behavior from through chick-rearing, helps induce formation of the , inhibits secretion of reproductive hormones after all eggs of a are laid, induces gonadal , facilitates start of molt; secreted by the of the ; abbreviated

upper section of the stomach; secretes digestive enzymes and hydrochlorid acid which break down food, including most bones, and pushes it on to the where are produced

nearer to the center of the body or to the beginning point of a body part; e.g. or "the is at the end of the " or "the humerus is to the wingtips"; "the base of a is to the "; opposite of ; Latin proxime = nearest

internet colloquial for "poop shoot," to expel metabolic and digestive wastes from the via the ; falconers use the term "" for this action in eagles and hawks

1 of 2 carpal () bones, the other being the ; at the end of the (arm) bone

smaller of the 2 bones of the forearm; slender and straight; to the other forearm bone, the ; photo; 3-D image of the wing bones including the and

regrowth, specifically in reference to a bird's gonads, which redevelop to functionality from a state of nonfunctionality (see gonadal ) as the breeding season begins, referred to as gonadal

the 12 flight feathers of an eagle's tail; pronounced “rek-TRY-seez”; the 2 central attach to the pygostyle (tailbone) by tendons and ligaments; Latin rector = “pilot” or “guide,” referring to the function of the tail feathers to steer the eagle's flight; sing rectrix

move backward, specifically in reference to a bird's gonads, which regress to a state of nonfunctionality at the end of each breeding season, referred to as gonadal (see also gonadal )

the 26 flight feathers of an eagle's wing (10 and 16 on each wing) that extend outward from the wing's trailing edge; pronounced 'REH-muh-jeez'; provide forward thrust and help control direction, provide lift; from Latin remex, meaning 'oarsman' or 'rower,' referring to the function of the wings to provide forward thrust in flight; sing. remex

hormone that helps raise low blood salt and blood pressure; secreted by the kidneys; abbreviated

soft membraneous keratin on the edges of the and of the , from the corner of the mouth to about halfway to the tip; pl. ricti

to shake the body vigorously to dry the feathers, fluff them to create greater insulation against cold or to cool off in hot weather, and to expel parasites

the timespan of darkness within a 24-hour day (Greek skotos = darkness)

a new layer of down feathers that begin to emerge by the second week after an eaglet hatches, from follicles interspersed among the follicles; they are thicker than the feathers with greater insulating capability; also called ; in eagles these feathers cover most of the body and hide but do not replace the feathers, which are pushed out by the emerging ; a few months after an eagle fledges the molts and is replaced by a new layer called definitive or adult down

the 16 flight feathers on the inner () portion of each wing; provide lift for flight

referring to species whose newly hatched chicks are near the low end of a spectrum of physiological development; eyes open but not yet able to focus, limited motor skills and strength and coordination, some downy feather covering but unable to thermoregulate, and fully dependent on parents for feeding, warmth, and protection for a long period before leaving the nest (); includes Bald Eagles and other raptors

decline in reproductive success as a result of aging

hard structure surrounding the , , , , and membranes, comprised primarily of calcium carbonate (calcite crystals), which are embedded in a small component of organic matter; Bald Eagle shells are ~ 0.56-0.6 mm thick (cf. ~ 0.28-0.4 mm for a chicken); thins during incubation as the absorbs some calcium for its bones; is produced in the of the in layers: base (mammillary) layer embedded in the outer , has cones or knobs (Latin mammilla = nipple) with organic material that produce calcite crystals, which grow upward to form columns comprising the palisade and vertical layers, with spaces between the columns reflecting cellular structure of the outer , finished with the thin (~ 0.005-0.01 mm) cuticle layer of proteins and organic material covering the surface; thousands of pores allow oxygen, carbon dioxide, and evaporated water to pass through the

2 thin layers of fibrous proteins lining the , essential components of the both in its development in the and in protecting and nourishing the growing ; surround the , , , and ; serve as a barrier against microbes from outside the , facilitate gas exchange and water evaporation from the , and may help maintain the 's structural integrity; the inner wraps around and holds together the ; the outer membrane lies tightly over the inner membrane and serves as an anchor for the during its development, when organic materials that produce calcium carbonate crystals intertwine with membrane fibers; the inner membrane separates from the outer membrane at the blunt end of the , forming an air cell, which increases in volume until it is pierced by the chick's as it nears hatch; this so-called triggers the chick's lungs and air sacs to begin their respiratory function; the develop in the of the before the is laid; low air humidity during hatching sometimes can dry the membranes and make them difficult for the chick to tear through

to expel metabolic and digestive wastes from the ; term used by falconers in reference to eagles and hawks, who expel wastes in a stream outward, as opposed to falcons and owls who expel wastes downward; colloquial (poop shoot)

archaic Old English and falconry word meaning to blow or wipe the nose, wipe the , or sneeze

moment when the Earth's exis is at its most extreme tilt in relation to the sun, and the sun is at either its highest or its lowest position in the sky, causing the duration of either day or night to be at its longest; happens twice a year, in the northern hemisphere on ~ June 20 (summer , when the sun is at its highest and day at its longest) and ~ December 21 (winter , when the sun is at its lowest and day is shortest); Latin sol = sun + status = standing still

hormone secreted by the in response to stress, suppresses hormones that would promote metabolism and growth; secreted by the to increase blood sugar and lipids; keeps and in balance; in breeding adults it can suspend reproductive activities and feather growth; abbreviated

male or germ cell, sometimes abbreviated to ; pl. spermatozoa

hatching of all eggs in a within a few minutes or hours of each other, occurs among most bird species; results from ; crucial for species (e.g. ducks, geese, swans, cranes, shorebirds), whose young are fairly well developed at hatch and leave the nest quickly

, a terminal on each ; comprised of the bone, surrounded by a thin layer of living tissue with nerves and capillaries, and covered by a thick, hard, dead sheath of beta-keratin; not homologous with a human toenail which has no bone or living tissue, and is comprised of alpha-keratin, less rigid and hard than beta-keratin

the , between the intratarsal () joint and the bases of

the toes; in birds consisting of the tarsal bones (the in humans) fused together with the metatarsal bones (the bones down to the toes); can be mistaken for a leg bone because it is longer than a human (see ); in Bald Eagles the lower portion of the is unfeathered; sometimes called simply the or the ; photo © Royal BC Museum with labels added

see

the science of classifying things according to their relationships to each other, especially in the disciplines of botany and zoology; classification is arranged from most general to least general: kingdom-phylum-class-order-family-genus-species; taxonomic classifications are in constant flux as scientists discover more details about relationships, especially because of DNA analysis; see the taxonomic classification of Bald Eagles here; also referred to as

the (outermost) bone of a , as the on a

paired male reproductive organs, in the abdominal cavity next to the top lobe of the kidneys; secretes hormones that stimulate courtship behaviors, gonadal , and development of

an androgen hormone, stimulates gonadal , production, and development, and development; may also induce synthesis in the liver; secreted by the and the ; abbreviated

gland below the sternum at the front of the neck, secretes hormones that aid in development of the immune system in young birds

gland at the base of the neck, secretes hormones for metabolism, regulation of body temperature, oxygen consumption, heart rate, blood sugar, and feather growth; also plays a role in gonadal , production of ova and , , and embryonic development

hormone that manages hormone secretions for metabolism and growth, especially in young birds; secreted by the of the ; abbreviated

type of hormone that stimulates the to produce its hormones; includes ; Greek tropos = change, reaction

hormone that stimulates secretion of hormones for growth, development, and metabolism; secreted by the ; abbreviated

hormone that controls bodily growth and development, stimulates gonadal hormones, and induces onset of molt and new feather growth; secreted by the thyroid; abbreviated T₄

see

lower leg bone, in birds consisting of the fused at the end together with the (upper) tarsal bones ( bones in humans), between the joint and the intratarsal () bone; the longest leg bone in most birds, including eagles; parallel with the much narrower , which fuses to it about two-thirds of the way down toward the (); photo of with on lateral side © Idaho Virtual Museum as licensed by Creative Commons

hormone that is critical to growth and development processes in embryos and young birds; contributes to secretions of reproductive hormones in breeding adults; secreted by the thyroid; secreted by the ; abbreviated T₃

larger of the 2 bones of the forearm; thick in diameter and slightly curved; to the other forearm bone, the ; secondary feathers attach to the side of the ; photo; 3-D image of the wing bones including the and

1 of 2 carpal () bones, the other being the ; at the end of the (arm) bone

paired glands below the , secretes a hormone that lowers blood calcium

thick, insoluble solution of metabolic wastes formed in the kidneys for expulsion through the at the end of the ; a more concentrated substance in birds (and reptiles and insects) than the urea formed in mammals and requires considerably less water to form or expel, thus allowing much greater retention of water for use in the body and eliminating the need for a bladder to hold water for excretion; in a developing is stored in the (one of the ) and is discarded after hatching; also

area of the between the and with tubules or grooves that can store a small number of after insemination; released to move up the to the to fertilize an when triggered by hormones, perhaps also by passage of an down the ; the amount of time can be stored and remain viable in Bald Eagles is uncertain, but may be as long as 2 weeks; stored may be less motile and thus less successful in fertilizing an than freshly inseminated

section of a female's between the isthmus and the vagina where water is added to the and then the hard calcium carbonate is laid down on the outer , surrounding the , , membranes, and ; a thin protein-rich layer called the cuticle covers the hard to prevent infection from penetrating the 's pores; the spends most of its time in the before ; also called the ; an area between the and the , the , can store from a male to be moved up the later to fertilize an in the

short, muscular section at the end of a female's ; after the has finished forming the that surrounds the (or the unfertilized ), , , and membranes, contractions (induced by the hormone ) push the into the , which helps push it into the middle section of the to be laid; has a robust immune component that prevents microbes in the from infecting the ; an area between the and the , the , can store from a male to be moved up the later to fertilize an in the

hormone secreted in the intestines to regulate the body's salt/water balance, induce relaxation of digestive muscles, and aid absorption of glucose and lipids; small amount secreted by the of the to stimulate nest-building and growth of ovarian follicles; secreted also by the to stimulate secretion of to encourage growth of mature ovarian follicles prior to ; secreted by the to induce release of other adrenal hormones in response to stress; stimulates metabolism and growth in young birds; abbreviated

single opening in the through which nitrogenous metabolic wastes (), digestive wastes (feces), and eggs and are expelled from the body

on the lower or abdominal side of the body or a part of the body; in contrast to ; Latin venter = stomach or belly

thin tissue surrounding the and , forming the ; consists of 4 layers, 2 formed in the (oolemma and perivitelline membrane) and 2 in the of the (middle continuous layer and extravitelline membrane); after the is ovulated into the , penetrate the perivitelline membrane to fertilize the , but the final, extravitelline membrane acts as a barrier to , preventing fertilization after it surrounds the ; Latin vitellus =

joint between the and bones of the wing and the fused bone of the (); comprised of the (unfused) and

rich repository of fats, proteins, carbohydrates, minerals, vitamins, and water that together with the nourish a growing ; lipids and proteins for a are formed in the liver and deposited in increasing quantity in an over several weeks time; granules become part of the cytoplasm (materials surrounding the nucleus) of the female germ cell (, the nucleus of the cell); is surrounded by 2 thin membranes while in the (oolemma and perivitelline membrane); when accumulates enough nutrients to feed a developing , the is ovulated into the ; 2 more membranes are laid down in the of the (middle continuous layer and extravitelline membrane); as the grows the is consumed and shrinks; absorbed into the 's abdomen by the time of hatching

membrane forming a pouch containing fats, proteins, carbohydrates, minerals, vitamins, and water to nourish the growing ; membrane is formed in layers around the and in the and the section of the (see ); in its first few days the growing pulls away from the , but blood vessels in the membranes connect the large through the abdominal wall to the 's heart; the shrinks as the gets larger and is absorbed into the 's body by the time of hatching

cell created by the union of a female () with a male (spermatazoan), with a full set of paired chromosomes, and undergoing cell division (growing); in birds, the female is heterogametic, with dissimilar ZW sex chromosomes, the male is homogametic, with similar ZZ sex chromosomes, so the female provides either the male or the female chromosome and thus determines the sex of the —the opposite of the case in mammals; becomes an when cell maturation and differentiation begin shortly after fertilization

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