Kinds of pigment:

Melanins

• pigments synthesized by birds
• brown, black, gray, red-brown, dull yellow, dull pink
• structural colors: blues & iridescent colors; ultraviolet colors (birds can see them, we can't)

• pigments birds cannot synthesize; obtained from plant material in diet
• bright reds, yellows, oranges

• greens

• white

• found in red, brown pigments of some birds (e.g. owls)
• bright pink-red; bright green in a few birds (turacos)

Environmental and genetic determination of coloration:

Melanins in juncos:

• in subspecies hybrids between parental types with red-brown back, black back, most offspring had red-brown in back; in addition had variable amounts of black pigment
• suggests: red dominant to no red; black and red melanins under different genetic control

• woodpeckers with all areas usually with melanic pigment white often have normal red patches
• suggests different control of melanin and carotenoid pigments

• yellow, orange, red shown in lab to depend on diet

• low carotenoid diets: both red and yellow shafted become pale yellow
• high carotenoid diets: red shafted become red, yellow shafted become yellow
• presence of carotenoids determined by diet; modification of carotenoids depends on enzymes that differ between the two subspecies
• red on head, face developed even on low carotenoid diets in both forms

Cryptic coloration

Structural support - melanins

Social signals

• dominance/ subordinance. Ex: Harris' Sparrows: size of black patch on chest associated with dominance.
• female preference.  Ex: House Finch: in lab, females spend more time with reddest males.  In field: with both natural coloration & dyed males, males with more red pair earlier.  Male color may indicate male quality: redder males had higher rates of feeding incubation females (G.E. Hill). Another Ex: Bluethroats (an European species): when ultraviolet pigment masked by sunscreen, males less attractive to mates.
• male-male interactions; territoriality.  Ex: Red-winged Blackbird: when red "epaulets" dyed black, tended to lose territories.  When feathers clipped, so red "epaulets" could not be concealed, received high aggression; tended to lose territories.

• one suggestion: birds are unprofitable because they can escape, so they advertise it.
• pied flycatchers: in one study, predators (falconiform) were more likely to attack dull colored female model than bright male model.  Other studies show different results -- inconclusive
• toxic birds: the pitohui and relatives, birds from New Guinea, contains toxin similar to that found in poison dark frogs.  Pitohuis are brightly colored, but it is not known whether this coloration evolved because they are toxic.

 Ex: gulls, many passerines
 Hypotheses:

• Survive better because cryptic (not well tested)
• Female mimicry allows "sneaky" matings (where tested, not supported)
• Receive less aggression from other males
• Example: Darwin's finches
• heritable variation in age at which black plumage obtained
• males that stay brown longer receive less aggression and survive better
• males that become black earlier obtain mates earlier