Bird colouration (Ornithology lectures 7 & 8)

Melanin

A pigment produced by oxidation and polymerization of the amino acid tyrosine in melanocytes; colors range from brown to black.

Melanocyte

Pigment-producing cell where melanin synthesis occurs.

Eumelanin

A type of melanin responsible for bold black to brown colors.

Pheomelanin

A type of melanin responsible for brown, rust, and golden colors.

Carotenoids

Diet-derived pigments that range from yellow to red; availability can limit coloration.

Unmodified carotenoids

Carotenoids deposited directly from the diet into plumage, typically yellow to orange.

Modified carotenoids

Chemically altered carotenoids produced from dietary precursors, often yielding red coloration (e.g., astaxanthin, canthaxanthin).

Structural colours

Color produced by feather microstructures that affect light reflection, not by pigments.

Iridescent coloration

Structural coloration that changes with viewing angle due to interference in feather nanostructures.

Non-iridescent structural colours

Structural colors that remain relatively constant with viewing angle.

Interference

Optical phenomenon where light waves combine; can be constructive or destructive, producing vivid colors in iridescent feathers.

Psittacofulvins

Red and yellow pigments produced inside parrots; exclusive to parrots and not strongly dependent on condition.

Turacin

Copper-based porphyrin pigment in turacos; gives red coloration and requires a copper-rich diet.

Turacoverdin

Copper-based porphyrin pigment in turacos; produces green coloration.

Biliverdin

A greenish eggshell pigment (a bile pigment) used in some birds; part of the eggshell pigment palette.

Porphyrins

Group of pigments with porphyrin rings; includes eggshell pigments and copper-based dyes that can produce red to green hues.

Eggshell pigments

Pigments such as biliverdin and porphyrins deposited in eggshells, influencing eggshell color.

Barbules

Microscopic projections on barbules of feathers that interact with light and contribute to structural coloration.

Barb

A primary branch of a feather extending from the rachis.

Rachis

The central shaft of a feather.

Cortex

Outer layer surrounding feather barbules, part of feather microstructure.

Spongy layer

Internal structural layer in feather barbules that participates in light scattering and color production.

Signals of Quality

Coloration signals indicating an individual’s health/fitness and used in mate choice, rival assessment, parent–offspring communication, and predator–prey interactions; typically costly and condition-dependent.

Signals of Fisherian attractiveness

Traits that evolve through Fisherian runaway sexual selection, coupling female preference with male trait genes and often leading to exaggerated ornaments.

Signals of Strategy

Coloration linked to advertising an individual’s behavioral strategy; predicts association between coloration and behavior (e.g., mating tactic or aggression).

Signals of Genetic compatibility

Signals used during mate choice to optimize genetic combinations (e.g., MHC compatibility), contributing to non-random mating and subspecies/species recognition.

Signals of Kinship

Signals used to identify unfamiliar kin, aiding mate choice, cooperation, and inbreeding avoidance.

Signals of Individual identity

Signals that facilitate recognition of signallers (mate, offspring, neighbor) and can support cooperation and reputation; often under negative frequency-dependent selection.

Signals of Presence

Signals used to advertise or conceal physical presence (e.g., for mate choice, territory defense, flocking, predator–prey interactions); can be honest or dishonest depending on context.

Carotenoids (in plumage)

Diet-derived pigments responsible for red/orange/yellow plumage; deposition reflects health/condition and underlies honest quality signaling.

Seven visual signal types (overview)

The seven broad information categories birds use: quality, Fisherian attractiveness, strategy, genetic compatibility, kinship, individual identity, and presence.

Runaway sexual selection

Process where female preference and male trait co-evolve, leading to rapid and exaggerated evolution of ornamental traits.

Intraspecific Variation in Coloration (birds)

Variation in coloration among individuals of the same species, influenced by factors such as genetics, environment, and social dynamics.

Why are queleas so variable?

Queleas exhibit high variability in coloration due to a combination of genetic diversity and environmental factors, which influence their mating preferences and social signaling. colorful and conspicuous-highly variable-sexually dimorphic-breeding season only-carotenoids involved.

Signals of Quality

Coloration signals indicating an individual’s health/fitness and used in mate choice, rival assessment, parent–offspring communication, and predator–prey interactions; typically costly and condition-dependent.
Representative Example: The bright red plumage of male House Finches, derived from carotenoids, signals their health and foraging ability to potential mates.

Signals of Fisherian attractiveness

Traits that evolve through Fisherian runaway sexual selection, coupling female preference with male trait genes and often leading to exaggerated ornaments.
Representative Example: The elaborate, unwieldy tail feathers of peacocks, which are a strong preference for females despite potential survival costs.

Signals of Strategy

Coloration linked to advertising an individual’s behavioral strategy; predicts association between coloration and behavior (e.g., mating tactic or aggression).
Representative Example: The distinct plumage morphs of male Ruffs (e.g., Independents, Satellites, Faeders) that correspond to different mating strategies and aggression levels.

Signals of Genetic compatibility

Signals used during mate choice to optimize genetic combinations (e.g., MHC compatibility), contributing to non-random mating and subspecies/species recognition.
Representative Example: Subtle visual cues in the plumage or displays of some passerine birds may allow individuals to assess genetic compatibility (e.g., MHC dissimilarity) in potential mates.

Signals of Kinship

Signals used to identify unfamiliar kin, aiding mate choice, cooperation, and inbreeding avoidance.
Representative Example: White-fronted Bee-eaters using calls and potentially subtle visual cues to distinguish kin from non-kin within their colony to direct cooperative breeding efforts.

Signals of Individual identity

Signals that facilitate recognition of signallers (mate, offspring, neighbor) and can support cooperation and reputation; often under negative frequency-dependent selection.
Representative Example: Many territorial songbirds recognize individual neighbors by unique visual displays and plumage patterns, leading to reduced aggression toward familiar individuals ('dear enemy' recognition).

Signals of Presence

Signals used to advertise or conceal physical presence (e.g., for mate choice, territory defense, flocking, predator–prey interactions); can be honest or dishonest depending on context.
Representative Example: A brightly colored male bird performing an elaborate display at a lek to advertise his presence for mating, contrasting with the camouflaged plumage of a ground-nesting bird designed to conceal its presence from predators.

Carotenoids (in plumage)

Diet-derived pigments responsible for red/orange/yellow plumage; deposition reflects health/condition and underlies honest quality signaling.

Seven visual signal types (overview)

The seven broad information categories birds use: quality, Fisherian attractiveness, strategy, genetic compatibility, kinship, individual identity, and presence.

Runaway sexual selection

Process where female preference and male trait co-evolve, leading to rapid and exaggerated evolution of ornamental traits.

Intraspecific Variation in Coloration (birds)

Variation in coloration among individuals of the same species, influenced by factors such as genetics, environment, and social dynamics.

Why are queleas so variable?

Queleas exhibit high variability in coloration due to a combination of genetic diversity and environmental factors, which influence their mating preferences and social signaling. colorful and conspicuous-highly variable-sexually dimorphic-breeding season only-carotenoids involved.