As a general rule among birds, if males and females are colored differently, the males are the more brightly colored. One needs only look at Cardinals, Bluebirds, and many species of waterfowl to get a sense of that rule; most often, the males show off for the females. And as a general rule, if the males-are-the-brightest rule is broken, the rule is broken only in species in which normal sex roles are reversed. Among North American species, the phalaropes are most famous for this, as the males tend the nests and the females might have more than one mate.
But the Belted Kingfisher seems to break both rules. The females are more brightly colored than the males, as they sport a rusty belt across beneath the blue belt shared by both sexes. Since the species breaks the first rule, one would expect it to follow the second rule and for the sex roles of the species to be reversed. One would expect females to rule the roost and males to be left to their own devices to raise the young. But there is no evidence for such role reversal in Belted Kingfishers. The species breaks both rules, leading to a small puzzle. Why are females seemingly brighter than males in this species?
As it turns out, Belted Kingfishers do not break either rule. The puzzle actually seems to be an example of human expectations and ways of seeing getting in the way of understanding the kingfisher. To most human ways of seeing, red is a bright, aggressive color. Put a bit subjectively, red is prettier than blue to the human eye. And so, when birders see a Belted Kingfisher, human predispositions lead to the assumption that the females are more brightly colored than the males, because it appears that way to human eyes. But Kingfishers have their own ideas of what makes females and males attractive.
Ariel White and Daniel Cristol, writing in the journal Waterbirds in 2014, studied how mercury affected the color of the Belted Kingfisher. They found a clear effect of mercury on coloration, but they also found that the chest bands of kingfishers vary by sex, with males showing “higher purityof blue at the dominant wavelengths.” Most field guides show this difference, with the blue belt of the female being tinged with rust and brown colored feathers. The pure white chest of the male, without the rufous belt as in the female, increases the reflectivity of the male chest, making the blue stand out even more. The brightness of the white, along with the clarity of the blue, seems to be the mark of an attractive male in this species.
The famous rusty belt of the female, for so long thought to be a sign that the species breaks the normal rules for birds, actually seems to decrease the reflectivity of the female’s chest. The red looks bright to human eyes, but to a kingfisher, the red actually disrupts the brightness of the white chest patch, which is what seems to count in this species. To kingfishers, the attraction rests in the blue and white, and the red of the female only mutes the white. The Belted Kingfisher actually follows the normal rules, but only when we see it through kingfisher eyes. Beauty may indeed be in the eye of the beholder, but one should always be careful that human ideas of beauty do not color our attempts to understand other species.
This article first appeared in the online edition of one of the very last issues of Bird Watchers' Digest.
Female kingfisher: Judy Gallagher, CC BY 2.0, via Wikimedia Commons
Male kingfisher: MarshBunny, CC BY-SA 4.0, via Wikimedia Commons
Comments