I once worked in an office in which a co-worker announced that the color red was aggressive, so red clothing should be disallowed in the workplace—or anywhere else!
Well! I’d always found red to be a rather cheerful hue, the color of ripe cherries and raspberries, of wild columbines and scarlet monkeyflowers, of holly berries and Santa Claus. There are some un-cheerful associations with that color, too, such as blood, but to ban a color entirely seemed excessive, to put it mildly. Perhaps you can guess what color my shirt was, the next day!
In the bird world, color is used as part of the process of attracting mates, as we have seen. Color (not just red) is also used to signal social status and levels of aggressiveness.
For example, black-capped chickadees, close relatives of our chestnut-backed chickadees, vary in the darkness of their black cap, and dark-capped individuals enjoy higher social status. Their greater dominance allows them better access to food in winter. House sparrows (those European introductions that can be seen in cities and farms all over the Lower Forty-eight) with high levels of testosterone develop large black patches on the chest. Big patches show other birds that these individuals would win a confrontation. And Harris’ sparrow males that have a high rank in the dominance hierarchy also have large black chest patches. The big black badges signal ‘don’t mess with me!’ There is an advantage both to the males with large patches and the subordinate males with small patches, because they can recognize each other’s status and avoid a direct fight.
White-throated sparrows breed across much of northern North America and occasionally wander into Southeast. Adults, both male and female, come in two color phases. One has black and white stripes on the crown of the head, and the other has brown and tan stripes there (as do juveniles). Detailed research has shown that the black-and-white-striped adults are more aggressive, spending much of their time chasing potential rivals. Although they often obtain and keep the best territories, they tend to neglect their parental duties. So if both members of a pair have black and white crowns, their nesting success tends to be low.
In contrast, a pair of brown-and-tan-crowned adults are less aggressive and markedly more attentive parents. They often lose battles with the black-and-whites and may be forced into suboptimal habitat, where even their better parenting cannot compensate entirely, so their nesting success also tends to be low. Thus, the most successful pairs of white-throated sparrows have one member of each kind: an aggressive black-and-white one and a parental brown-and-tan one.
Experiments with eastern bluebirds (whose appearance is much like the western one) have shown that males with brighter blue plumage out-compete the duller males in contests over nest boxes. So the brighter males get the best nest boxes, and get them earlier, which also gives them first choice of females. I’m tempted to speculate that, like bright mountain bluebirds, they also do well in obtaining extra-pair copulations.
Red-winged blackbird males have red epaulets with a yellow border. In aggressive encounters with each other, they show off these bright red patches by flaring the wings and erecting the feathers. (You can sometimes see them in the marsh by the Pioneer’s Home or in the big marsh on Eagle River.) They can cover the epaulets with black feathers on the upper back when they want to sneak into a neighbor’s territory unaccosted by the owner. In this case, the optional display of color signals not social status but level of aggressiveness.
In an earlier essay, I noted that much of the variety of color and pattern that we see in the animal kingdom is the result of mate choices and competition to be attractive to the other gender. Another portion of the array of colors and patterns can now be seen to be a result of signaling social status and level of aggression.
I have not addressed the matter of color with respect to camouflage, or signaling age or gender or species, or mimicry, or warning colors, and so on. But all of these things contribute to the diversity we see. Perhaps in a future essay…?