The Language of Birds’ Feathers
All birds’ feathers tell a unique story. Sometimes, these stories lead to new understandings of nature.
There is something more to birds’ extravagant feathers than their colors or their frills. Behind the fantastic array of shapes and hues are messages, communicated in the same way that we communicate with signs, with advertisements, with our own clothing.
But unlike what are, to us, merely forms of individual expression, birds’ plumage communicates messages that are life and death. It sends signals upon which the next generation relies. It lays out patterns that protect from certain predatory death.
When one really digs into birds as scientific subjects, this ‘plumage puzzle’ becomes indescribably tantalizing. One’s mind is filled to the brim with questions, a spring of curiosity that wells up with every glance at a bird. Suddenly woodpeckers are endlessly mysterious. What could they possible be communicating with all those checkered patterns? Why are male Northern Cardinals all red? What are bluebirds really saying with their blue backs? To some of the questions like these, we have answers, but to most, we have nothing but speculation.
What we do know is that there will undoubtedly be an answer to these questions. It is impossible that any living thing would look as ridiculous as a Raggiana Bird-of-Paradise just because it could. There must be some benefit to it. Why? Because ridiculousness is costly. It takes time and energy to grow such magnificent plumes, which really are impressively complex, even at the microscopic level. With psychedelic color also comes the risk of predation. Colors make birds as obvious to predators as they do to us.
In nature, unless you have a reason, spending more than you have to is a death wish.
So what is the reason? In many cases, it is simply this: information. In growing colorful plumage, birds are sending a message to all beholders, a message that they are healthy enough to grow colors in the first place. Given the costs of this colorful self-decoration, it is truly impressive indeed that so many birds have them. In overcoming the costs and growing crazy plumages anyway, birds are showing off just how healthy they are, just how smart they are, and ultimately, how good their genes are.
This information is perhaps the most important message sent at any time in a bird’s life. Why? Because the next generation depends entirely upon it. If a male bird has sub-par plumage compared to his peers, discerning females will notice. With sub-par plumage, the male may not have access to good food sources, or may be genetically impaired in some way. When a female bird is in search of a mate, the harsh natural world requires that she look elsewhere.
If she did choose the poorly feathered male, a number of things could happen to her chicks. Most obviously, he may not have access to nutritious foods to help raise the chicks that are then more likely to starve. This is the first scenario where genes aren’t passed on. He may also have poor genes for survival in general. By mating with him, the female is passing on his lower quality genes to her offspring, which will then also have a lower chance of survival in nature. This is the second scenario. Either way, if all her chicks die within the first year, it’s unlikely that her preference for sub-par plumage — if it’s genetically based — will propagate in the population. All is lost, with nobody’s genes — male or female — passed on. Simple as that.
So you see, having good plumage to send clear messages of health is extremely important to females who want to ensure a fighting chance in life for their offspring. Similarly, males want to pass on their genes just like females do, and as such, males with better plumage often outcompete males with poorer plumage. This same logic is used by males just as it is by females. In many species, males will only mate with females who have good plumage, so the choosiness goes both ways.
Taking a step back now from the nitty-gritty of sexual selection, the point is this: birds’ feathers are laden with messages just waiting to be decoded. I surmise it would be very difficult to find a part of any bird’s plumage that is colored without a reason.
In invite you to ponder the coloration in the following birds:
Now then, intrepid explorers, to the field! There is work to be done in decoding nature’s many secrets! In the language of color, birds are some of the most exciting study subjects out there. Most birds have a balance between camouflage and signals in their plumage, but this balance is different for every species. There is much, indeed, to explore, much to decode, much to translate into our spoken and written words.
What better place to start than Peru? Peru exhibits a biologist’s dream: extreme biodiversity around the Amazonian lowlands, a long coastline, and a vast mountain range. This means varied biomes, varied climates, varied yearly and seasonal cycles, varied species — variety, which as you know is the spice of life, is in abundance in Peru.
We can explore this variety without even visiting…through field guides. Better yet, we can do this reclined in a chair, sipping coffee, pondering the universe through birds and their diverse plumages, as I was doing recently.
And I found it! A lead worth digging, and as is often the case with me, it’s about the many mysterious messages in plumage.
In the New World, there exists an immensely diverse family called the Tyrant Flycatchers, or the Tyrannidae. This family has filled a fittingly immense number of niches throughout the Americas, becoming especially diverse in South America. To illustrate, this one family takes up more than ten percent of the number of plates in Birds of Peru — a field guide that depicts 1,817 species.
Within this family, there exists a genus called Contopus. North Americans may be familiar with such Contopus as Eastern Wood-Pewee or Olive-sided Flycatcher. This genus has representatives all the way from boreal forest in Canada to parts of southern South America. Like many flycatcher genera, most Contopus species are drab olive-green with few distinguishing markings.
In Peru, there are six representatives of this genus. And oddly enough, two of these species are dark charcoal gray, totally in opposition to the norm with this genus…why?!
These little anomalies are the stuff of discovery. While they may seem inconsequential, these details are where we find new understandings of why life exists as it does, how the environment guides evolution, and how living things interact.
So these two anomalous Contopus — Blackish Pewee and Smoke-colored Pewee — what could possibly explain their entirely dark-gray plumage? Without any markings, could the whole plumage be a signal to other individuals of the same species? Could it be camouflage in dark environments?
Following this path of inquiry, we find that ecologists have been remarking on a preponderance of darker plumages in humid environments for almost 200 years. There even exists an ‘ecological rule’: Gloger’s Rule, a summation of these observations named for zoologist Constantin Wilhelm Lambert Gloger, states that populations will be paler in dry environments, and darker in dank environments. Are these dark Contopus adapted ‘more’ to their tropical habitats than their olive-green counterparts? That wouldn’t make sense. Contopus are all migratory, right?
Wrong! It turns out this is the distinguishing factor: the gray Contopus are all sedentary, staying in the same dank environments all year. The olive-green Contopus, on the other hand, are migratory, staying in tropical Peru for only part of the year.
Aha! We have what could be a correlation.
But as of yet, it seems extremely likely that no one has studied this anomaly. And without study, we are indeed limited to speculation. I must keep digging.
Above all else, not all science blogs end with answers. Some end with open doors. To some, this open door says is labeled ‘unknown’, while to others, it’s labeled ‘discovery’.
Which door do you see?
