What is the main characteristic that distinguishes birds from other vertebrates?
You guessed it...feathers! (Beaks and wings would also have been good answers). But did you know that there are no fewer than 𝟳 𝗱𝗶𝗳𝗳𝗲́𝗿𝗲𝗻𝘁𝗲𝘀 𝘀𝗼𝗿𝘁𝗲𝘀 𝗱𝗲 𝗽𝗹𝘂𝗺𝗲𝘀, which are distributed over the bird's body according to their role? Some are used for flying, others for warmth, and still others for showing off or camouflage, depending on the season (and the bird's ego)...
Firstly, there are the three most visible types of feathers on the bird's body. The 𝗿𝗲́𝗺𝗶𝗴𝗲𝘀 are the stiff, but flexible, elongated feathers that cover most of the bird's wings. They are 𝗲𝘀𝘀𝗲𝗻𝘁𝗶𝗲𝗹𝗹𝗲𝘀 𝗽𝗼𝘂𝗿 𝗹𝗲 𝘃𝗼𝗹. The 𝗿𝗲𝗰𝘁𝗿𝗶𝗰𝗲𝘀 are also used for flying, and make up the bird's tail. As their name suggests, they provide direction during flight. Finally, the 𝘁𝗲𝗰𝘁𝗿𝗶𝗰𝗲𝘀, also known as contour feathers, are found on the bird's body. It is these that 𝗰𝗵𝗮𝗻𝗴𝗲𝗻𝘁 𝗱𝗲 𝗰𝗼𝘂𝗹𝗲𝘂𝗿 𝗽𝗲𝗻𝗱𝗮𝗻𝘁 𝗹𝗮 𝗽𝗲́𝗿𝗶𝗼𝗱𝗲 𝗻𝘂𝗽𝘁𝗶𝗮𝗹𝗲, often becoming more colourful in males, and becoming dull again at the end of summer, the better to hide from potential predators. You only have to look at the Green-winged Teal, for example, to see the difference between the nuptial plumage of the male and that of the female.
Less visible, but nonetheless part of the 𝗽𝗹𝘂𝗺𝗮𝗴𝗲 (all of the bird's visible feathers), are the 𝘀𝗲𝗺𝗶-𝗽𝗹𝘂𝗺𝗲𝘀 𝗲𝘁 𝗹𝗲 𝗱𝘂𝘃𝗲𝘁. Hidden beneath the tectrices (remember; body feathers), the semi-feathers look very much like them, but have hooks (barbs) that give them a fluffy appearance. These serve 𝗱'𝗶𝘀𝗼𝗹𝗮𝘁𝗶𝗼𝗻 𝘁𝗵𝗲𝗿𝗺𝗶𝗾𝘂𝗲, just like down. Down, however, lies directly against the bird's skin and has no hooks; it is a soft, silky feather. Humans have drawn inspiration from 𝗲𝘅𝗰𝗲𝗹𝗹𝗲𝗻𝘁𝗲𝘀 𝗾𝘂𝗮𝗹𝗶𝘁𝗲́𝘀 𝘁𝗵𝗲𝗿𝗺𝗶𝗾𝘂𝗲𝘀 𝗱𝘂 𝗱𝘂𝘃𝗲𝘁 to make quilts. Down is sometimes the sole plumage of chicks and ducklings. As the chick grows, it will begin to develop remiges and may start to fly. That's when you can shout 'fly, little bird'.
Next: the 𝘃𝗶𝗯𝗿𝗶𝘀𝘀𝗲𝘀 (or silks). These 𝗽𝗿𝗼𝘁𝗲̀𝗴𝗲𝗻𝘁 𝗹𝗲 𝘃𝗶𝘀𝗮𝗴𝗲 and the eyes of certain species, such as owls. Finally, the best for last, we have the 𝗳𝗶𝗹𝗼𝗽𝗹𝘂𝗺𝗲𝘀, the most mysterious feather of all; these are tiny feathers, which look like hairs, and which are the 𝗿𝗲́𝗰𝗲𝗽𝘁𝗲𝘂𝗿𝘀 𝘀𝗲𝗻𝘀𝗼𝗿𝗶𝗲𝗹𝘀 𝗱𝗲𝘀 𝗽𝗹𝘂𝗺𝗲𝘀. It is these feathers that allow birds to track and 𝘀𝘂𝗿𝘃𝗲𝗶𝗹𝗹𝗲𝗿 𝗹𝗲𝘂𝗿𝘀 𝗰𝗵𝗮𝗻𝗴𝗲𝗺𝗲𝗻𝘁𝘀 𝗱𝗲 𝗽𝗹𝘂𝗺𝗮𝗴𝗲. Recent research even shows that filoplumes could send signals to make new feathers, when some are broken or lost.
In waterfowl, the tectrices are waterproof (rather practical, in fact). As well as preventing our little flying friends from constantly catching a cold, these feathers trap a layer of air, which helps them float. For more information on how waterbirds avoid catching a cold in winter, please refer to the excellent book 67th 60seconds ...'Cold as a duck!
Information from Marc Duquet, allaboutbirds.ch
Photo Credit: Kai Taimsalu
