Mad about Science: Feathers

By Brenden Bobby
Reader Columnist

You probably haven’t put a lot of thought into the contents of your down comforter, or the luxurious throw pillows on your couch. They’re stuffed with feathers, so what? You can find half a dozen crow feathers on the side of the road walking from the library to Travers Park.

Feathers are an old biological adaptation, yet a relatively complex one in the way they function and are utilized. Feathers are not simply made for flying, nor are all feathers useful for flight. The primary function of most feathers throughout evolutionary history has largely been for insulation.

Many birds, particularly in cool-weather climates, use down in exactly the same way humans use down blankets. The loose and fluffy feather structure is well-suited to trapping dead air as an insulation material, which keeps endothermic animals like humans and birds warm by trapping their body heat and not letting it escape into the open air. Down is an adaptation of the feather structure that is heavily varied from the slim blade-shaped feathers we often associate with birds.

Down is very loose and fluffy, designed to create space and air gaps, while typical blade-like feathers have tiny ridges that interlock and seal with oil to become waterproof. Both of these structures are different from protofeathers. Protofeathers are relatively rare to see today, as birds have gone through hundreds of millions of years of evolution to adapt to today’s climate, yet you can get a glimpse of protofeathers every year at a farm and feed store like Carter Country, the Co-Op or North 40 Outfitters.

Baby chicks are covered in a form of down that closely resembles the protofeathers of ancient dinosaurs. They sport short, pointy hollow spike-like feathers that develop while the chick is in the egg, and even more once it has hatched. These feathers offer minimal protection from the elements — this seems counterintuitive at first glance, as chicks are extremely vulnerable to even tiny temperature fluctuations for the first two weeks of their life. However, they have evolved in a way that they are dependent on a fully grown hen’s developed down in order to survive.

Many evolutionary traits have a singular purpose or function they accomplish, having developed over countless generations to perform that task. Feathers have taken a different approach, often serving multiple functions that aren’t immediately apparent. Utilizing the parent’s feathers to warm offspring is one of these unexpected adaptations. Another is the ability to intimidate both predators and prey.

Early feathered creatures from the Cretaceous Period may have been incapable of flight, despite being covered from head to toe in feathers. Caudipteryx was a small, feathered dinosaur from the early Cretaceous, roughly 124 million years ago. It likely resembled the cross between a turkey and a velociraptor. Its arms, while feathered, were far too small to achieve flight, and the environment in which it lived was believed to be very warm, so what was the purpose of its feathers?

It’s possible that Caudipteryx developed showy, high-contrast feathers in order to exploit a synaptic response in its prey, which were highly mobile insects like grasshoppers hardwired with a rapid-fire flight response when presented with surprising stimuli. Many insects to this day are wired this way, hiding in a spot until something frightens them and triggers a reflexive response to leap and flee. Humans aren’t well adapted to catching insects like this, and our response is often something similar: jumping in fright or becoming very alert for the presence of more insects. Birds, however, utilize scare tactics to frighten insects out of their hiding places and strike at them when they are out in the open. This is called flush-pursuit and is a foraging tactic still used by birds to this day.

Proving this on a 120 million-year-old cadaver is virtually impossible, but it stands to reason that this may have been one of the primary roles feathers provided on a bird in this kind of environment when it couldn’t fly. Over time, as insects evolved and became more agile, it’s likely that gliding and flight became a more appealing trait to avian dinosaurs, so feathers and arms evolved to match this need. Avian dinosaurs that were able to thrive naturally outcompeted those that could not, and so these adaptations and mutations grew into new species of dinosaurs, and later birds.

Over millions of years, feathers evolved to also communicate silently with other birds. Peacock feathers are the most obvious example by displaying intense colors to peahens in a mating display. Birds such as the ruffed grouse will perform a rhythmic thumping with their feathered wings to serve as a call to other birds and potential predators.

Over time, feathers evolved into specialized shapes for specific functions. We are all familiar with the typical blade-shaped feather, but did you know they are actually asymmetrical? The asymmetry of the feather reduces force on the front-facing edge of the feather which prevents the feather from twisting during flight. This gives the bird greater control in flight by allowing each feather to act as an individual airfoil, generating lift as air passes unevenly over the surface.

Who knows what we might look like if we manage to survive for 240 million years? Personally, I’m pulling for hot dog fingers.

Stay curious, 7B.