Ornithology Exam 1 Vocabulary

Feathers

Unique outgrowths of the skin, they are filamentous, flexible, and lightweight structures made primarily of beta-keratin, which are essential for insulation, temperature regulation, lift and thrust during flight, camouflage, and communication

Beak

Also referred to as a bill, this is a distinctive attribute of all birds. It varies greatly in form and function but is always toothless and covered with a horny sheath (the rhamphotheca) in modern birds. This structure functions in food acquisition, as the mouth cannot break up food

Gizzard

Known anatomically as the Ventriculus, this is a thick muscular organ with a hard sandpaper-like lining and grit that performs the mechanical breakdown of food in birds. It is a functional analogue of mammalian molars and is specialized to process unmasticated food. Its morphology varies significantly depending on the bird's diet, from being nearly vestigial in frugivorous birds to being extremely powerful in grain eaters

Uncinate Processes

Horizontal projections found on the ribs of birds that serve to strengthen the body skeleton & facilitate breathing

Furcula

The fused clavicle that strengthens the skeleton and acts like a flexible, elastic spring that compresses and rebounds in rhythm with the wing beat during flight

Carpometacarpus

The structure formed by fused hand bones (digits) in the wing, which supports and maneuvers the large, powerful primary flight feathers

Tibiotarsus

A unique fused leg bone found in birds, formed by the fusion of the tibia and some tarsal (foot) bones. It is positioned above the ankle joint, contrasting with the tarsometatarsus, which is below the ankle joint

Tarsometatarsus

One of the unique fused leg bones of birds, positioned below the ankle joint, which combines the foot bones (tarsals) and metatarsals, enabling the bird to walk on its toes

Hallux

The large, reversed, opposable first rear toe (digit I), which is unique among vertebrates and improves a bird’s capacity to grip branches or prey

Endothermic

A core characteristic of birds, meaning they are warm-blooded and maintain a high, constant body temperature, typically ranging from 40°C to 44°C

Eggs

A characteristic feature of birds is that they lay these. The avian embryo is in a cleidoic (closed) structure, which contains all the nutrients and water required by the embryo for its early development. Birds lay these for external incubation due to their high body temperatures. This structure is one of the most complex reproductive cells in the animal kingdom

Syrinx

The unique sound-producing structure in birds, located near the junction where the trachea branches into the two bronchi; it provides birds with complex and diverse vocal capabilities unmatched by other animals

Adaptive Radiation

A process defined as the rapid divergence of a lineage from a common ancestor to occupy diverse ecological niches, resulting in a large variety of species morphology, such as the observed diversity in avian beak shapes

Maxilla

This term refers to the upper mandible. It is described as a flattened, hollow, bony cone in the avian beak

Trabeculae

These are a complex system of bony struts that internally reinforce the maxilla (upper mandible) of the avian beak, adding strength with little weight

Rhamphotheca

The horny sheath that covers the exterior of the avian beak or bill, which is always toothless in modern birds

Cranial Kinesis

The ability of many birds to flex or bend the upper half of the bill at the nasofrontal hinge (located between the bill and skull). This feature allows for specialized actions, such as woodcocks opening just the tip of their bills while probing

Adaptation

The enhanced fit between the organism and its environment. This concept is seen within birds, ranging from morphology and physiology to migration and mating systems, and testifies to the pervasive role of Darwinian evolution

Natural Selection

The process described as the differential survival of individual organisms with advantageous traits. If these advantageous traits are heritable, the process results in adaptive evolutionary change across generations. It is described as a process "without plan or purpose"

Convergence

The independent evolution of similar adaptations in unrelated organisms. This process is caused by adaptation to similar ecological roles, leading unrelated species of birds to become superficially similar in appearance (phenotype) and behavior

Biogeography

The study of the geographical distributions of plants and animals, which helps define the six major faunal regions of the Earth, each having its characteristic birds

Endemic

Species or taxa that are geographically restricted and found only within a specific, limited region of the planet

Avifaunas

The regional assemblages of bird species within a defined biogeographic region, formed by a mixture of species whose histories involve adaptive radiations, dispersal, isolation, and extinction events

Archaeopteryx lithographica

The earliest known fossil bird, discovered in 1861 and known from the late Jurassic period (~150 MY old) in Germany. It is considered a transitional form between reptiles and modern birds, exhibiting a mosaic of reptilian features (such as teeth, a long bony tail, and gastralia/free belly ribs) and avian features (such as feathers with asymmetrical vanes, a furcula/wishbone, and a backward-pointing first toe)

Phylogeny

The explicit history of genealogical relationships among organisms. It refers to the great Tree of Life, depicting the evolutionary history of organisms, which provides a foundation for taxonomic classification

Occipital Condyle

A single ball-and-socket device that serves as the articulation point between the skull and the first neck vertebra in both birds and modern reptiles

Stapes

The single bone (also called the columella) found in the middle ear of both birds and reptiles

Tarsal Bones

The bones of the foot in which the ankle joint is located in the middle in both birds and modern reptiles

Archosaurs

A specific monophyletic group of reptiles that includes the alligators, crocodiles, dinosaurs, pterosaurs, and birds

Antorbital Fenestra

A distinctive hole in the side of the skull in front of the eye socket. It is a shared, derived feature of archosaurian reptiles

Vanes

The planar surfaces on either side of the shaft (rachis) of a feather. In the primary wing feathers of Archaeopteryx, these were observed to be asymmetrical, which is common in nearly all flying birds

Phylogenetic Tree

A branching diagram used to depict the history of shared evolutionary relationships among organisms. The branches represent historic species evolving through time

Clade

A natural group of organisms that includes all the descendants of a single common ancestor. It is also known as a monophyletic group

Derived Character State

A shared evolutionary innovation or new evolutionary feature that is shared by the members of a group and is used to recognize clades

Primitive Character State

A feature that is inherited from a common ancestor but cannot tell us which organisms are more closely related. For example, the presence of feathers is primitive to living birds

Homologs

Similarities inherited from a common ancestor. The wings of all birds are examples of this

In-group

In phylogenetic comparison, the group of organisms being analyzed when determining the polarity (direction) of a character's evolution

Out-group

Organisms that are more distantly related to the group being investigated, used for comparison to interpret the direction of evolution of a character

Ornithischians

A main, monophyletic group of quadrapedal vegetarian dinosaurs, including Stegosaurus and Triceratops

Sauropods

The long-necked vegetarian dinosaurs of the Saurischian clade, which included the largest animals to have ever lived, such as Brachiosaurus

Theropods

The clade of bipedal, meat-eating dinosaurs (Saurischian dinosaurs) that includes Tyrannosaurus rex and Velociraptor. Birds are living theropod dinosaurs

Pubic Boot

A broad expansion on the end of the long pubis bone that characterizes the tetanurans, a theropod group that evolved from the common ancestor of carnosaurs and birds

Clavicle

The paired chest bones that are fused to form the furcula (wishbone) in birds. This bone structure evolved early within the theropod dinosaurs

Pneumatic Bones

Air-filled bones, such as ribs, vertebrae, and wing bones, that are penetrated by small branches of the membranous, nonvascular air sacs that are part of the unique avian respiratory system. Similar bones are found in various theropod dinosaurs

Semilunate Carpal

A crescent-shaped bone in the wrist shared by dromaeosaurs, troodonitids, and Archaeopteryx. This bone allowed for lateral hand movements contributing to wing folding and the flight stroke

Ulna

The trailing bone of the forearm. Quill knobs (where secondary feathers attach) are found on the trailing edge of this bone in birds and some theropods like Velociraptor

Quill Knobs

Small bumps on the trailing edge of the ulna (forelimb bone) that develop where secondary wing feathers are attached. Their presence in theropods like Velociraptor suggests they had secondary feathers

Thecodonts

An obsolete term historically used for a poorly characterized group of more ancient archosaurs, proposed by Heilmann as the ancestral group from which birds evolved. This group is now known not to be monophyletic

Pygostyle

A special bone created by the fusion of caudal vertebrae at the tip of the short avian bony tail. The tail feathers (rectrices) insert on this bone

Alula

Also called the bastard wing, it is a tiny group of asymmetrical feathers on the tip of the first digit of the hand. When extended, this structure helps maintain laminar air flow and prevents stalling at slow speeds

Arboreal Theory

The hypothesis for the origin of flight proposing that flight started with gliding and parachuting from elevated perches (the "trees down" approach).

Cursorial Theory

The hypothesis for the origin of flight proposing that elongated forelimbs enhanced leaping ability in a small, bipedal theropod dinosaur that ran and jumped (the "ground up" approach)

Systematics

The study of diversification of life on Earth, which involves investigating the evolutionary relationships (phylogeny) among organisms through comparisons of fossils, preserved specimens, behavior, and the genetic code (DNA). The goal of this study is to discover the historic relationships of organisms

Taxonomy

The science of naming and classifying organisms, including birds, according to standardized rules. It is the formal, hierarchical system of names attached to species and higher groups of organisms.

Taxon

Any group of animals that is recognized in a classification. The Class Aves is an example that includes all species of living birds.

Hierarchy

A structure of nested sets of groups with increasingly closer relationships. Linnaeus proposed that all organisms could be classified in this manner, which Charles Darwin later discovered was the result of evolutionary history.

Lineage

A group of organisms sharing a more recent common evolutionary history. In a phylogeny, the lines depict this, which are interbreeding populations of organisms in the past. Related taxa constitute an evolving history of this that diversifies over time.

Monophyletic

A natural group of organisms, also called a clade, that consists of an ancestor and all of its descendants. Each higher taxon recognized in classification is hypothesized to be this.

Conservative Characters

Features or traits that do not change much in the course of ecological adaptation. They are of greater value for discovering older branches of a phylogeny because they retain evidence of ancient ancestors.

Anisodactyl

The primitive condition in birds where the hallux (digit I) points to the rear and three toes (II, III, and IV) point forward. This is the toe arrangement found in most perching birds.

Zygodactyl

A foot arrangement where the first (I) and fourth (IV) digits point backward and the second (II) and third (III) digits point forward. This arrangement has evolved multiple times in groups such as woodpeckers and parrots.

Heterodactyl

The toe arrangement unique to trogons, where the first (I) and second (II) toes are directed backward.

Syndactyl

A foot arrangement where two or three toes (specifically toes II and III) are fused basally. This characterizes the Order Coraciiformes (kingfishers and allies) and various families of perching birds.

Pamprodactyl

The foot arrangement in which the positions of toes I and IV are not fixed, allowing all four toes to point to the front. This characterizes mousebirds and some swifts.

Genome

The complete set of genetic material of an organism. Avian’s are generally smaller than those of mammals and other reptiles.

Species

Fundamental units of biological classification. In binomial nomenclature (the Linnaean system), this name is the second, uncapitalized, italicized name of an organism.

Biological Species Concept (BSC)

A definition of species put forth by Ernst Mayr, stating that species are "groups of interbreeding natural populations that are reproductively isolated from other such groups".

Phylogenetic Species Concept (PSC)

An alternative definition of species considered by ornithologists, which is based on the phylogenetic history of lineages.

Evolutionary Species Concept (ESC)

An alternative definition of species considered by ornithologists, which is based on the phylogenetic history of lineages.

Speciation

The process by which new species are formed. It occurs through the division of one species into two or more descendant species, typically resulting from the genetic divergence of isolated populations.

Beta-keratin

A fibrous protein polymer that feathers consist of primarily. This protein is unique to birds and other reptiles, forming the hard structures of reptilian skin and the scales, claws, and beaks of birds, with feather keratins being a special class characterized by a small deletion in their molecular sequence.

Contour Feather

A typical body feather that defines the outline or contour of the bird’s body. It possesses a long central shaft and a broad, flat, planar vane.

Vane

The broad, flat, planar surface found on either side of the central rachis of a contour feather. The surface of a pennaceous feather vane is created by the zippering interactions between the microscopic structures on adjacent barbules.

Calamus

The tubular, hollow base of the shaft (or quill) that anchors the feather firmly into the follicle in the skin. It is produced by the undifferentiated epidermal tube as feather growth ends.

Follicle

Specialized organs in the skin from which feathers grow. It is a tubular in-pocketing of the epidermis that grips the feather by the calamus using a combination of muscular forces and friction.

Rachis

The main portion of the central shaft of a feather, extending outward from the calamus, that supports the feather vanes. It is formed by the fusion of barb ridges on the dorsal side of the feather germ tube.

Barbs

The primary lateral branches that extend off the rachis, creating the structure of the vane. Barbs grow and subsequently fuse to the rachis during development.

Ramus

The tapered central axis of a single barb (plural: rami). The ramus contains a core of medullary cells and is covered by cortical cells.

Barbules

Rows of smaller branches projecting from both sides of the ramus of a barb. They interlock with others of their kind from adjacent barbs to create the coherent surface of the pennaceous vane.

Cortical Cells

The outer layer of flattened cells that are composed of solid keratin and surround the spongy core of the ramus.

Medullary Cells

Larger, box-shaped cells that form the spongy core of the ramus. These cells are empty and air-filled, contributing to the structural strength of the barbs.

Barbicels

Projections borne by the cells of the barbules, which may be elaborate and hooklike. The loss of these barbicels on contour feathers (e.g., in cormorants) is an adaptation for diving.

Distal Barbules

Barbules that extend toward the tip of the feather vane. These structures feature tiny hooklets that zipper the vane by connecting with the grooves of the proximal barbules of the neighboring barb.

Proximal Barbules

Barbules that extend toward the base of the feather. They feature prominent grooves that interlock with the hooklets of the distal barbules of the neighboring barb, completing the vane’s zippering mechanism.

Plumulaceous

Describing the fluffy, downy portion of the feather vane, which is usually found deep within the plumage and characterized by long, thin, flexible barbules. This structure provides insulation.

Nodal Prongs

Small projections found at the junctions of neighboring barbule cells on downy (plumulaceous) barbules. They are homologous to the hooklets and other projections on pennaceous barbules.

Afterfeather

A secondary, usually plumulaceous structure found on some contour feathers. It is a mirror-image rachis and vane attached to the same calamus and functions primarily to enhance insulation.

Aftershaft

The condition where the afterfeather is reduced to only a simple rachis.

Remiges

The long, stiff, pennaceous wing feathers. These feathers create the aerodynamic forces (lift and thrust) that propel birds in flight.

Retrices

The flight feathers of the tail. They attach to the pygostyle (fused caudal vertebrae) and are crucial for control, steering, and braking during flight.

Primaries

The outer (distal) remiges that attach to the bones of the hand and the second digit. They are strongly asymmetrical in shape, with the leading-edge vane being narrower than the trailing vane.

Secondaries

The inner (proximal) flight feathers of the wing. They attach to the trailing bone of the forearm (ulna) and typically have blunter tips than the primaries.

Pennulum

Long, filamentous tips on the distal barbs of the leading-edge vanes of owl primaries. They create a fuzzy surface texture that reduces air turbulence, enabling the silent flight typical of most owls.

Down

Soft and fluffy (plumulaceous) feathers. They provide excellent lightweight thermal insulation and water repellency due to their highly flexible barbs and barbules.

Natal Down

The down feathers of chicks. This plumage typically lacks a rachis and grows from the same follicles that will later produce pennaceous contour feathers.

Filoplumes

A very distinct class of hairlike feathers that function in monitoring the movement and position of adjacent, vaned feathers. Their fine rachis transmits disturbance signals to sensory corpuscles within the follicle.

Bristles

Specialized, simplified feathers that consist only of a stiff, tapered rachis with a few basal barbs. They serve sensory and protective functions, often found on the head as eyelashes or around the mouth.

Powderdown

Special feathers that produce dustlike beta-keratin particles (resembling talcum powder). These particles are dispersed over the plumage during preening, with disputed functions including waterproofing or defense against parasites.

Molt

The process by which feathers are replaced regularly and periodically throughout the life of the bird. This comprehensive and controlled replacement occurs seasonally and with age, allowing the bird to replace worn feathers.

Epidermis

The outer layer of the skin. It is composed of cells that will eventually keratinize and die when they mature. It forms the outer, descending layer and the inner, ascending layer of the tubular feather follicle.