Just returned from East Texas a short while ago. Did some birdwatching of course but saw nothing exotic or unexpected, but I was struck by the difference in coloration in East Texas birds compared to those at my home in Northern California. The Blue Jays were a striking blue and black and white, making our western Scrub, Steller’s, and Pinyon Jays look drab in comparison. The Brown Thrasher’s shiny brown plumage looks almost iridescent compared to the Sage Thrasher; the Red-headed Woodpecker is a standout with its red head and deep white and black body- no other woodpecker compares. And then there’s the Northern Cardinal whose bright red plumage almost sparkles as it flies and when perched looks like a Christmas decoration.
Ok, there are certainly attractively colored birds out west like the Western Tanager, Vermillion Flycatcher, and hummingbirds, but these are not your common, everyday backyard birds like the Blue Jay and Northern Cardinal. And how about the elegant Scissor-tailed Flycatcher and Eastern Kingbird compared to the muted colors of the Ash-throated Flycatcher (that name is duller than the bird) and the Western Kingbird, a pretty but not as stylish a bird?
Are birds east of the Rocky Mountains more colorful and if so, why would that be?
Well, to make a broad generalization, we know that these birds evolved many thousands of years ago without human civilization as we know it. The deciduous forests of eastern North America were denser than the coniferous and mixed woods of the West. So, like the thick tropical forests of the world, color is helpful to identify yourself to mates or competitors. But the downside of being easily seen is that predators can find you too.
In the more open forests of the west mates and competitors can be located more easily and the muted colors are less obvious to those that might eat you.
If my idea is correct, the birds that live in the midwestern grasslands ought to be the dullest colored of all: consider the Horned Lark, Savannah Sparrow, and Short-eared Owl.
Another study says that brighter colored birds in Australia are found in the less tropical, but wet/dry season environments. In a wet season, the birds need bright coloration to find each other. So my idea is supported here. The drier western U.S. has duller birds than the wetter eastern half and the dullest are in the dry grasslands.
But things are not that simple. A study on the evolution of bird coloration surmises that predation pressure is the major factor determining bird coloration. “Some birds with bright plumage patterns are known to be unpalatable compared to cryptic species, and certain other patterns have been interpreted as adaptations to confuse predators. Bright colors may commonly be favored when an individual is obvious (e.g. through activity) and where it represents an ‘unprofitable’ prey for a predator.” Sort of like poisonous frogs or butterflies.