Bird Plumage
A bird’s plumage is composed of patterned feathers and pigments that produce remarkable effects on its appearance. Bright yellow, green, and blue colors make up the plumage of the Many-colored Rush-Tyrant of South America (Photo above).
The other extremes are drab gray olive or brownish birds, such as many shorebirds and tyrant flycatchers. Color patterns in bird plumage result from adaptations to habitats and species’ behavior. Birds use plumage patterns throughout their lives, whether for concealing or signaling purposes.
Broad Classification of Bird Plumages
Among the nearly 10,000 species of birds, the plumage patterns can broadly be divided into mottled, scaled, barred, and spotted. Males, females, juveniles, and breeding and non-breeding plumages may all display a combination of these broad plumage patterns.
Studies on bird plumages have shown that a mottled pattern tends to function well in stationary camouflage. Plumages that regularly repeat a pattern, such as bars, scales, and spots, function in motion camouflage. Examples of the broad classification of bird plumage patterns in birds include:
Mottled Plumage: The feathers of birds with mottled plumage have heterogeneous pigmentation. The feathers are pigmented heterogeneously. In both males and females, this pattern is found on the upperparts more frequently than on the underparts, but it is less frequent in males.
Scaled Plumage is a plumage pattern where pigmentation follows the feather’s edge, giving a scaled effect. Scaled plumages are less prevalent and frequently biased towards adults’ upperparts and juveniles’ underparts—Female Blue-winged Teal (Anas discors).
Barred Plumage is made of alternating dark and light pigmentation transversal to the feather’s axis. Barred plumages are frequently found on the underparts of breeding adult males, but also in juveniles.
Spotted Plumage is a pattern where one or more spots pigment each feather. Spotted plumages are also frequently found on the underparts of breeding males and females, adults and juveniles.
Are birds self-aware of their plumages?
It is evident that birds choose where to forage, nest, and rest from a mosaic of many backgrounds or substrates available to them. However, it is not clear how birds choose places to suit their appearance. The evidence suggests the birds must have a sense of self-awareness of how they relate to their environment.
Ornithologists suggest that “It could be that somehow they ‘know’ what they look like and act accordingly.” Furthermore, birds may look at themselves, their eggs and the background and substrates and decide whether it’s a good place to forage for food, rest, and nest safely. Alternatively, birds may learn over time and multiple attempts about the kinds of situations they were not being detected by predators or their eggs escaped being eaten.
Plumage Pattern and Function
Concealment
The need for a plumage that protects from predation via camouflage and is optimal for sexual signals at the appropriate time and environment has resulted in the development of intricate plumages in birds. Animals display diverse coloration patterns that are thought to function as camouflage. To prevent detection by predators, birds match the background or break up (disrupt) their outline creating false edges.
Concealment is thought to be the main goal of bird color patterns — not just cryptic ones but also of many birds that are brightly colored and bold. The predominant visual aspect of many plumage colors is their similarity to the bird’s usual environment.
For example, ptarmigans are nearly pure white in the winter when they blend in with the snow. When patches of snow remain on the alpine meadows in spring, the birds are white and brown. In summer, when herbs and lichen cover the rocks, ptarmigans are finely barred black and brown.
Plumage and Posture
Some birds have taken camouflage a step further and adopted a posture that helps them match their background even more. The common potoo of Tropical America looks for dead branches or stumps that resemble its plumage to nest and day-roost. Its camouflage typically works well when the bird is relaxed. When a threat approaches, a potoo will adopt an upright position to line up its body outline with the perch and make it look like a bird, and the pole is one piece.
A more familiar example is the American Bittern. This bittern points its bill skyward, aligning its body contours and the stripes on its breast with the surrounding vertical marsh grasses.
Reduction of Contrast
Some bold color patterns reduce the contrast between a bird’s shape or outline and its background. The breast band of small plovers, a classic example of the disruptive pattern, visually separates the outline of its head from that of its body.
To be most effective, the contrast between elements of a bird’s plumage should be similar to the contrast between elements in the background. Thus, the color and sizes of patches or mottles on a bird’s plumage provide the most effective concealment when they match the color and size of the background elements.
Nightjars that spend the day on the forest floor’s leaf litter have mottles of sizes and tones that resemble the surrounding leaf litter. The boldly patterned plumages of tanagers and wood warblers blend with the small leaves, branches, reflections of light, and shadows found in their arboreal habitats.
Countershading and Concealment
The lower reflectivity of the upper parts of a bird interacts visually with the contrasting color of the underparts to disguise its outline, helping the bird match its background. The value of contrast increases with the intensity of illumination from above. Open country birds such as plovers have strongly contrasting colors on their upperparts and underparts. White underparts work particularly well in this regard as a neutral reflector that takes on the nearest surface’s color tone, in this case, the ground.
White breasts and bellies on small plovers function more effectively for countershading than white breasts on large, long-legged shorebirds. The underparts of long-legged shorebirds are farther from the sand or muddy surfaces and have dark underparts rather than white.
Reverse Countershading
While countershading (dark upperparts and white underparts) helps concealment, reverse countershading (White upperparts and dark underpants) makes birds conspicuous. Breeding male Bobolinks (Dolichonyx oryzivorus) and Black-bellied Plovers (Pluvialis squatarola) have striking reverse countershading. They need to be as noticeable as possible for a short period of time during the mating season when attracting females is the most important goal.
Plovers are also most conspicuous to predators, but they spend most of their time vigilant, continually scanning their surroundings for females and predators during the mating season. Food is abundant during this period, and they do not need to spend much time foraging for food. Once the mating season is over, bobolinks and plovers molt into plumages that make them inconspicuous in the habitat they favor in the wintering grounds. Most male ducks are dressed to impress during the breeding season. They molt into brown feathers during the non-breeding season.
Plumages that Enhance a Bird’s Outline
Contrary to concealment, some bird plumages are highly visible and do not typically match the natural background elements. Some birds, mostly males, developed conspicuous plumages to enhance their visibility. Scientists have asked whether brightly colored birds or those with plumages that do not match the background are more susceptible to predation and are at a disadvantage.
Field experiments revealed that predators do not always attack bright-colored plumages. The unexpected result may be explained by the fact that brightly colored males often are more cautious and tend to spend more time in dense foliage than females and birds with less conspicuous plumages. Predators may not attack brightly colored birds because they may be more difficult to catch than their drab-colored counterparts.
The all-red Northern Cardinal (Cardinalis cardinalis) uniform coloration enhances its outline and renders it more conspicuous than a mixed color pattern. The crest probably enhances this effect. Contrasting edgings enhance striking signal patches such as the white crest of the Hooded Merganser (Lophodytes cucullatus).
The flamboyantly patterned plumage of a Torrent Duck (Merganetta armata) seems as if it would stick out in its habitat. However, finding one in the tumbling rapids of a stream when the bird is foraging can be challenging.
Final Remarks
Learning the fundamentals of birds’ plumage patterns adds a new dimension to your enjoyment of birds and birding skills. The next time you see a nightjar on a day roost, you will know why the bird spends the day on such a particular spot.
Likewise, a whitish-gray Black-bellied Plover on its way to the breeding grounds will molt into a plumage that defies camouflage rules and makes it highly visible.
If you visit the Tropics, you will better understand why tanagers, honeycreepers, and toucanets are brightly colored. You will also understand why antbirds and flycatchers of the forest’s understory have such subdued plumages.
References:
- Foster, Dr. Rory; Smith, Dr. Marty. “Bird Feather Types, Anatomy, Growth, Color, and Molting.” Veterinary & Aquatic Services Department. peteducation.com. Archived from the original on 9 February 2017. Retrieved 10 April 2017.
- Frank B. Gill. 1990. Ornithology. W. H. Freeman and Company. New York.
- Lindsay L. Farrell, Clemens Küpper, Terry Burke, and David B. Lank (December 2014). “Major Breeding Plumage Color Differences of Male Ruffs (Philomachuspugnax) Are Not Associated With Coding Sequence Variation in the MC1R Gene” (PDF). White Rose Research Online.
- Marius Somveille, Kate L.A. Marshall, and Thanh-Lan Gluckman. A global analysis of bird plumage patterns reveals no association between habitat and camouflage. Academic Editor: Scott Edwards. PeerJ. 2016; 4: e2658. Published online 2016 Nov 9.
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