You do not need a degree in natural science to become familiar with the different ways that birds use camouflage to either evade the notice of predators or the notice of prey, or both of these. Some birds have the advantage of plumage designs that mask the outline of their bodies, disrupt recognition of their shape or even disguise which direction they are looking or heading.
An example of this asset is the head pattern such as the white “chin strap,” of a Canada goose. The goose’s head would be more easily discerned if it were all black or all white. The diffuse vertical striping of a brant along its sides is irregular, hard to read and does not seem to fit into the distinct jet black, bright white and uniform gray-brown of its other design features. Also consider the design of a drake common eider and see how the mostly black and white elements conspire to defy a recognizable head outline and overall volume.
Camouflaging plumage, the ability to blend into the immediate environment, is a tactic that we see a lot in birds that are vulnerable to predators and that have learned to blend in to avoid detection. Examples include nesting female birds, their young, birds that feed on the ground (like sparrows) and birds that spend a lot of time in leafy tree habitat (female tanagers), in grassy habitat (grouse, rails, meadow larks) or in snow habitat (ptarmigan, snowy owls). The birds have adapted their appearance through thousands of generations to the extent that often movement is the only useful key to their presence, and movement is something they can control. They seem indistinguishable from the background features common to their habitat.
Owls are the stars of dissembling ( I was going to say “standouts,” but that word is contrary to my point). They are a group that is able to blend so well and stay so still during daylight hours they go unnoticed hiding in full view. Warbler and vireo species that favor the yellows and muted greens of their breeding territories have a way of becoming difficult to distinguish from a backdrop of dappled foliage in spring and summer when they are on the nest or feeding young and need to go unnoticed.
Cryptic coloration serves a broad selection of bird types. Mallard hens, Virginia rails, female red-winged blackbirds, marsh wrens, swamp sparrows, Wilson’s snipe, all these and many others that inhabit similar marshy habitats show significant adaptation to blend into the grasses, cattails and reeds of the terrain where they spend most of their lives. If they did not, their genes would likely have been discarded in the evolutionary process.
Countershading, where the feather surfaces that face the sunlight are dark and the feathers that are in shadow are light, is a very common strategy (not just in birds) that is often referred to as a means of disrupting a predator’s recognition of a bird’s shape and the shadow it throws. One more tactic for the cryptic is posture, whether it is a plover crouching in the sand, a bittern elongated in the marshland or a nightjar resting in broad daylight posing as a branch.
There are instances where the effect of a diffuse feather pattern goes even further to control what our eyes see. What I have come to recognize, chiefly because I take so many photographs of birds, is that there are certain birds whose feather patterns defy our ability to accurately focus on them. This particular feature is more readily observed once the camera has frozen the bird’s motion for us, and we can look carefully at the feather patterns, or sometimes the lack of feather patterns. I assume this characteristic also serves to protect these birds from their natural predators.
While there is symmetry to the pattern and the arrangement of flight feathers — it makes good sense to have both sets of wing feathers equal — the alignment of back, mantle, head and neck feathers on some species may appear asymmetrical, further disrupting the more common alignments thus blurring recognition of identity and shape.
This feature is true in at least three local species: the yellow-bellied sapsucker, brown creeper and the downy young of a piping plover. In examining the photographs of these species I have wondered why my eyes were unable to focus well when looking at certain areas of feathering, even though I knew the photograph was in focus. Two of these species spend almost all their time moving from one part of a tree to another along the tree’s bark. Usually their backs are exposed to the rest of the world so it makes sense for the bird to look like bark. The baby piping plover, on the other hand, besides being the color of the sand where it makes its home, also retains its down for a number of days after hatching. The young plover’s down makes it very hard to define against its beach background. They hardly have an outline at all and their only recognizable features are their dark eyes, the small black bill and their oversized pinkish legs. The rest simply does not register very well without those recognizable features and the bird’s definition more or less evaporates.
Essentially, they remain a blur. Or a blur with eyes, beak and legs.