Birds of a Feather

What do you imagine when you hear the word “feather”?

It’s likely that you imagine a tail or wing feather. But did you know there are 6 major types of feathers on a bird’s body? Each of the major types has specific form and function.

Let’s start by defining two important terms in regards to feather structure. A feather is either pennaceous or plumulaceous. Pennaceous feathers are what most people imagine to be a “typical” feather. Pennaceous feathers are flexible and consist of the following parts:

  • Vane-  the flat surface of a pennaceous feather
  • Barbs- hundreds of stiff filaments that attach to a rachis
  • Rachis- a relatively solid structure that extends down the middle of the feather
  • Ramis- a central shaft which has slender branches on either side
  • Barbules- the slender branches on either side of the ramis.
  • Barbicels- tiny hooklets that attach the barbules together and create the flatness of the vane
Anatomy of a feather (Image via

Plumulaceous feathers have barbs that are loose and fluffy. Their barbs have rami that are less stiff and the barbules are usually either reduced or thinner. As a result, plumulaceous feathers cannot hold anything except a delicate, rounded form. When you see a chick with down, you are seeing an example of plumulaceous feathers.

Feathers grow out of and remain attached to a feather follicle in the epidermis. If you’ve ever seen the bumps on a plucked chicken, then you have seen feather follicles.

Now that we’ve discussed the basics of feather structure, let’s examine the 6 major feather types.

Major Feather Types (Image via Bird Academy/Cornell Lab of Ornithology)

1. Down Feathers

These feathers are entirely plumulaceous, making them soft and fluffy. Down feathers act as insulators that allow birds to manage their internal body temperatures by thermoregulation. There are 3 types of down feathers.

  • Natal Down temporarily covers the entirety of a hatchling’s body. Birds that are precocial (able to feed/tend to itself immediately after hatching, therefore not relying on a parent) tend to have more natal down since they have to maintain their temperatures on their own. Altricial birds (who rely on a brooding parent) have sparse natal down since they receive heat transferred by a parent.
  • Body Down lies under the contour feathers of many adult birds. These are more common in waterbirds such as penguins, loons, and ducks. Ever see a duck or goose line its nest with feathers? These are body down from their breast.
  • Powder Down are unique because they grown continuously and disintegrate at the tips to produce a keratinous “powder”. They help make feathers waterproof, and are only found in certain kinds of birds, such as pigeons and herons.

2. Contour Feathers

These feathers give a bird their characteristic shape and make up its exterior. The top section of these feathers are pennaceous, while the bottom section is plumulaceous. Many birds can use oil from the uropygial gland at the base of the tail to help their contour feathers repel water. Contour feathers have a variety of functions including aiding in thermoregulation, streamlining the body during flight, and social displays.

Great Egret showing off its nuptial plumes (Image by BirdNation)

3. Flight Feathers

Flight feathers make up the majority of the tail and wing feathers. They are almost completely pennaceous. The anterior and posterior edges of flight feathers are asymmetrical. The leading edge (a.k.a anterior edge) is typically thinner than the trailing edge (a.k.a posterior edge).  This feature allows flight feathers to stabilize under the pressure of air currents during flight. These feathers are usually the stiffest and largest feathers on a bird. There are 2 types of flight feathers:

  • Remiges originate from the wings and attach to the bone. The feathers of the outer wing are called primaries and the feathers of the inner wing are called secondaries. The number of primary and secondary feathers vary by bird, but typically a bird can have between 9-12 primaries and 8-32 secondaries.
  • Rectrices  form the tail surfaces/airfoil of a bird. The central pair of rectrices attach directly to the tailbone. Like remiges, number of retrcies vary by bird size, but is typically between 6-32.

Coverts are smaller contour feathers that overlap the wing and tail feather and create the streamlined shape that is important to the aerodynamics of flight.

The rectrices and remiges of a Bonaparte’s Gull (Image by BirdNation)

4. Semiplumes

Semiplumes are the intermediate form between the contour and down feathers. Their barbs usually lack hooks, so their vanes are not pennaceous. They occur at the edges of contour feather tracts and complement the insulation of down feathers.

5. Bristles

Bristles are highly specialized and lack barbs along most of its length. Their rachis are very stiff and they are almost exclusively found on a bird’s head. The most common type are rictal bristles, which commonly project at the beak’s base. Many birds that are insectivores, like flycatchers, have rictal bristles.

6. Filoplumes

Filoplumes are hair-like feathers and are the smallest of all the feather types. They have a rachis but few or no barbs. They’re usually hidden underneath the contour feathers. Instead of feather muscles, they have sensory receptors in their skin near the follicles. Filoplumes aid birds in detecting changes in feather position caused by body movement or wind.

Feathers are an amazing adaptation that is unique to birds. Knowing the types of feathers helps us appreciate how complex and special birds are.

Hooded Merganser preening (Image by David Horowitz)

My New Avian Journey

So yesterday, I teased that I would be starting a new bird-related journey soon. Well, without further ado:



I will be taking the Cornell Lab of Ornithology’s Comprehensive course in Bird Biology!

If you’ve been reading my blog for awhile, I’m sure you know that the Cornell Lab of Ornithology is one of my favorite places. It’s one of my main sources of avian information and we even took our 2016 vacation to Ithaca, NY specifically to go birding at the Lab (you can read about that here and here). As a Lab member, I’ve spent countless hours on their website reading articles, watching videos, taking webinars, and watching bird cams.

So when I learned about their Bird Biology class, I knew I had to take it. My dream is to be a Conservation Biologist/Environmental Scientist/Ornithologist, which is why when I’m not at my non-science related full-time job, I’m taking night/summer classes as a biology major. But when I found out about the Lab’s course, I knew it would exactly what I needed to start moving forward with my goals.

The Lab’s Bird Biology course is a university-level self-study course that anyone interesting in birds can take. The course was developed was by one of my favorite ornithologists, Dr. Kevin McGowan, as well as Dr. Sarah Wagner. (Side note: I took a webinar with Kevin McGowan a few winters ago: Odd Ducks and Wandering Waterfowl. If you’re interested in identification courses I recommend checking out his classes/webinars). The course consists of using the textbook (pictured above) and online resources, as well as multiple tests and quizzes for each chapter.

Pretty much anything you would want to know about birds can be found in this course. Topics covered throughout the 700-page book include anatomy, evolution, migration, vocal behavior, social behavior, ecology of populations, and flight to name a few topics. I’m so excited to dive even further into the avian world and share some of the information I learn with you!

If your interesting in learning about the Cornell Lab’s Bird Biology course check out their website.


The Most Perfect Thing

I am a pretty avid reader, and as you might guess, I spend a lot of time reading about birds. I decided that I wanted to share these books with you. So today is the first BirdNation book review. If you read this blog I assume that you have an interest in birds, so I thought you may find some worthwhile reading material through this feature.

I just finished reading The Most Perfect Thing: Inside (and Outside) a Bird’s Egg by Tim Birkhead. Tim Birkhead is a British zoologist and works at the University of Sheffield as a professor of behavior and evolution. He has written numerous book about birds and their behaviors, including the popular Bird Sense in 2012. In this book, Tim Birkhead takes you on a journey of how the egg is developed. The journey begins in late 19th century England with oologist (a scientist who studies bird eggs) George Lupton. George Lupton had an extensive collection of Common Guillemot eggs, which are now in the Natural History Museum in Tring, Hertfordshire, England. Birkhead refers to George Lupton and Common Guillemots as his prime example throughout the text. Along the way we learn about other scientists who made contributions to bird biology and egg production, as well as learn about the eggs of numerous bird species.

The Most Perfect Thing by Tim Birkhead (Image by BirdNation)

Birkhead starts with the outside of the egg and work his way in. The first few chapters talk about the structure and physical appearance: egg shape, shell thickness, and color. There are two chapters concerning color. Birkhead first talks about how eggs become the colors they do and then talks about why.

The middle chapters of the book are about what happens inside the egg and focus on the albumen and the yolk. The albumen, also know as the “egg white”, forms around the yolk. It provides nutrients for the embryo and protects the yolk. The albumen is mainly 90% water and 10% proteins. The egg yolk is the primary food supply for the embryo. Birkhead goes into detail about these subjects and there are detailed diagrams throughout the book to help the readers visualize these features.

The final sections of the book are all about laying, incubating, and hatching. Topics explored include how the egg leaves the oviduct (where eggs travel from the ovaries to outside the body), incubation lengths of different species, and the process of how the chick leaves the egg (which is not as quick as you would think!).

The Most Perfect Thing is a fascinating book. Although everyone is familiar with eggs, many people don’t know about the process of egg formation and hatching, so it’s an eye-opening and amazing process to learn about. I would recommend this book to anyone who is interesting in learning about the science behind eggs. It is not a leisurely read, however. Besides the history portions about Lupton and other scientists/studies, most of this book reads like a text book. One thing I like about Tim Birkhead is his ability to make these scientific studies accessible and easy to understand to casual readers as well as more science-minded individuals. Even if you are a casual reader, I recommend this book if you are into learn about bird biology and want to know more the science of eggs. There are so many amazing thing to learn through this book. I’m sure by the end you’ll agree that the bird egg is as close as you can come to The Most Perfect Thing.